SquashfsHandler: backport 7-Zip 26.01 ReadBlock bounds-check hardening - #262
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SquashfsHandler: backport 7-Zip 26.01 ReadBlock bounds-check hardening#262tonghuaroot wants to merge 1 commit into
tonghuaroot wants to merge 1 commit into
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Upstream 7-Zip 26.01 (released 2026-04-27) hardened
CHandler::ReadBlock() against two attacker-influenced inputs in
malformed SquashFS images:
1. The bounds check before the final memcpy was
if (offsetInBlock + blockSize > _cachedUnpackBlockSize)
which can wrap when offsetInBlock + blockSize overflows UInt32.
26.01 rewrites it in overflow-safe subtractive form:
if (_cachedUnpackBlockSize < offsetInBlock ||
_cachedUnpackBlockSize - offsetInBlock < blockSize)
2. For fragmented file inodes, `offsetInBlock = node.Offset` is taken
directly from inode metadata. 26.01 adds a sanity check that
`offsetInBlock <= _h.BlockSize` before proceeding, so an inode
that claims an offset beyond the block size is rejected up-front.
Patch matches upstream 7-Zip 26.01 source.
Signed-off-by: tonghuaroot <tonghuaroot@gmail.com>
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Backports two
CHandler::ReadBlock()hardenings landed in upstream 7-Zip 26.01 (released 2026-04-27).What changed upstream
The bound just before the final
memcpy(dest, _cachedBlock + offsetInBlock, blockSize)was```cpp
if (offsetInBlock + blockSize > _cachedUnpackBlockSize)
return S_FALSE;
```
which is overflow-prone if
offsetInBlock + blockSizewraps a 32-bit add. 26.01 rewrites it in overflow-safe subtractive form:```cpp
if (_cachedUnpackBlockSize < offsetInBlock ||
_cachedUnpackBlockSize - offsetInBlock < blockSize)
return S_FALSE;
```
For fragmented file inodes,
offsetInBlock = node.Offsetis taken directly from inode metadata. 26.01 adds a sanity checkoffsetInBlock <= _h.BlockSizeimmediately afterwards so an inode that claims an offset beyond a block is rejected up-front.Impact
A crafted SquashFS image with attacker-controlled
node.Offsetnear0xFFFFFFFFcombined with a smallblockSizecan wrapoffsetInBlock + blockSizebelow_cachedUnpackBlockSizeand pass the check, after which thememcpyperforms a length-controlled OOB read past_cachedBlockand writes the bytes into the caller'sdestbuffer.Patch
Two small hunks, byte-for-byte matching upstream 26.01.
Disclosure
I am not a native English speaker. AI tooling was used to polish the prose in this PR description. The fix itself is a direct backport from upstream 7-Zip 26.01 source; no design choices were made beyond matching upstream verbatim.