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Fix #129691: heap buffer overflow when writing unaligned data to .blend file #129821

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Jacques Lucke merged 2 commits from JacquesLucke/blender:no-aligned-write into main 2024-11-05 15:51:58 +01:00
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Jacques Lucke commented 2024-11-04 21:13:43 +01:00
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writedata used to align the written buffer size to a multiple of 4. This causes multiple issues:

  • Writes uninitialized data.
  • Crash with ASAN due to a heap buffer overflow if the buffer is not any longer than what is passed in.
  • Modifies the length of the buffer which can't be undone when reading the buffer again.

I don't know of any reason for this alignment here. I'd think that it doesn't matter when writing to a file. If it would matter, then we should probably align to at least 8 nowadays because that's the alignment of pointers.
The original reason for this alignment seems to be lost to history. It was already part of the initial commit:

source/blender/blenloader/intern/writefile.c Lines 427 to 428 in 12315f4d0e
len+= 3;
len-= ( len % 4);

See #129691 (comment) for an ASAN report that is caused by this alignment.

`writedata` used to align the written buffer size to a multiple of 4. This causes multiple issues: * Writes uninitialized data. * Crash with ASAN due to a heap buffer overflow if the buffer is not any longer than what is passed in. * Modifies the length of the buffer which can't be undone when reading the buffer again. I don't know of any reason for this alignment here. I'd think that it doesn't matter when writing to a file. If it would matter, then we should probably align to at least 8 nowadays because that's the alignment of pointers. The original reason for this alignment seems to be lost to history. It was already part of the initial commit: https://projects.blender.org/blender/blender/src/commit/12315f4d0e0ae993805f141f64cb8c73c5297311/source/blender/blenloader/intern/writefile.c#L427-L428 See https://projects.blender.org/blender/blender/issues/129691#issuecomment-1330891 for an ASAN report that is caused by this alignment.
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Jacques Lucke added 1 commit 2024-11-04 21:13:53 +01:00
fix
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73c0e220d8
Jacques Lucke commented 2024-11-04 21:14:25 +01:00
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@blender-bot build

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Jacques Lucke requested review from Campbell Barton 2024-11-04 21:15:35 +01:00
Jacques Lucke requested review from Bastien Montagne 2024-11-04 21:15:36 +01:00
Campbell Barton approved these changes 2024-11-05 02:28:43 +01:00
Jacques Lucke added 1 commit 2024-11-05 11:08:29 +01:00
Merge branch 'main' into no-aligned-write
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129f684d3d
Jacques Lucke commented 2024-11-05 11:08:46 +01:00
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Bastien Montagne approved these changes 2024-11-05 15:48:12 +01:00
Bastien Montagne left a comment
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Don't see any reason for this half-broken alignment either, so since @ideasman42 does not have anything against the patch either, fine by me.

Don't see any reason for this half-broken alignment either, so since @ideasman42 does not have anything against the patch either, fine by me.
Jacques Lucke merged commit 9d87291c40 into main 2024-11-05 15:51:58 +01:00
Jacques Lucke deleted branch no-aligned-write 2024-11-05 15:52:02 +01:00
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