SquashfsHandler: backport 7-Zip 23.00 LzoDecode UInt32 widening (CVE-2023-40481) - #257
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…2023-40481) Upstream 7-Zip 23.00 changed the `back` offset computation inside LzoDecode() so that the source byte is widened to UInt32 before the shift, preventing a signed-overflow which can cause an out-of-bounds write while extracting a crafted SquashFS image. p7zip carries the pre-fix line and is therefore reachable from the same crafted image. The change is a single-line widening cast equal to upstream 23.00: - back = (b >> 2) + (*src++ << 2); + back = (b >> 2) + ((UInt32)*src++ << 2); The next branch in the same function (mode == 4 path) was already using `((UInt32)src[1] << 6)` in p7zip, so the surrounding code style matches. Signed-off-by: tonghuaroot <tonghuaroot@gmail.com>
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Backports the one-line UInt32 widening landed in upstream 7-Zip 23.00 to address CVE-2023-40481 (ZDI-23-1164) in the SquashFS handler's LZO decoder.
What changed upstream
7-Zip 23.00 changed
CPP/7zip/Archive/SquashfsHandler.cppinsideLzoDecode()from:to:
Without the cast,
*src++is aBytepromoted toint, and<< 2on the resultingintis performed in signed arithmetic. Together with the subsequent additions, this can compute abackoffset that overflows past the destination buffer, giving an out-of-bounds write while extracting a crafted SquashFS image.p7zip's
LzoDecode()carries the pre-fix expression at line 1047 and inherits the same flaw. The next branch in the same function (mode == 4path) already uses((UInt32)src[1] << 6)in p7zip, so the surrounding code style is consistent with the cast.Patch
Single-line widening, byte-for-byte the same as upstream 23.00:
p7zip has a precedent of backporting CVE fixes one at a time (e.g. #239 for CVE-2021-3520, #254 for the NTFS ClusterSizeLog bound).