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038505c41f
Backport the relevant part of upstream commit 5b266196 [0]. This fixes in-place decompression for x86-64 kernel decompression. It uses a bound of 131072 + (uncompressed_size >> 8), which can be violated after upstream commit 6a7ede3d [1], as zstd can use part of the output buffer as temporary storage, and without this patch needs a bound of ~262144. The fix is for zstd to detect that the input and output buffers overlap, so that zstd knows it can't use the overlapping portion of the output buffer as tempoary storage. If the margin is not large enough, this will ensure that zstd will fail the decompression, rather than overwriting part of the input data, and causing corruption. This fix has been landed upstream and is in release v1.5.4. That commit also adds unit and fuzz tests to verify that the margin we use is respected, and correct. That means that the fix is well tested upstream. I have not been able to reproduce the potential bug in x86-64 kernel decompression locally, nor have I recieved reports of failures to decompress the kernel. It is possible that compression saves enough space to make it very hard for the issue to appear. I've boot tested the zstd compressed kernel on x86-64 and i386 with this patch, which uses in-place decompression, and sanity tested zstd compression in btrfs / squashfs to make sure that we don't see any issues, but other uses of zstd shouldn't be affected, because they don't use in-place decompression. Thanks to Vasily Gorbik <gor@linux.ibm.com> for debugging a related issue on s390, which was triggered by the same commit, but was a bug in how __decompress() was called [2]. And to Sasha Levin <sashal@kernel.org> for the CC alerting me of the issue. [0] |
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| .. | ||
| huf_decompress.c | ||
| zstd_ddict.c | ||
| zstd_ddict.h | ||
| zstd_decompress.c | ||
| zstd_decompress_block.c | ||
| zstd_decompress_block.h | ||
| zstd_decompress_internal.h | ||