Description

In the Linux kernel, the following vulnerability has been resolved:

erofs: fix lz4 inplace decompression

Currently EROFS can map another compressed buffer for inplace
decompression, that was used to handle the cases that some pages of
compressed data are actually not in-place I/O.

However, like most simple LZ77 algorithms, LZ4 expects the compressed
data is arranged at the end of the decompressed buffer and it
explicitly uses memmove() to handle overlapping:
__________________________________________________________
|_ direction of decompression --> ____ |_ compressed data _|

Although EROFS arranges compressed data like this, it typically maps two
individual virtual buffers so the relative order is uncertain.
Previously, it was hardly observed since LZ4 only uses memmove() for
short overlapped literals and x86/arm64 memmove implementations seem to
completely cover it up and they don't have this issue. Juhyung reported
that EROFS data corruption can be found on a new Intel x86 processor.
After some analysis, it seems that recent x86 processors with the new
FSRM feature expose this issue with "rep movsb".

Let's strictly use the decompressed buffer for lz4 inplace
decompression for now. Later, as an useful improvement, we could try
to tie up these two buffers together in the correct order.

Classification

CVE ID: CVE-2023-52497

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 5.08% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/9ff2d260b25df6fe1341a79113d88fecf6bd553e
https://git.kernel.org/stable/c/a0180e940cf1aefa7d516e20b259ad34f7a8b379
https://git.kernel.org/stable/c/77cbc04a1a8610e303a0e0d74f2676667876a184
https://git.kernel.org/stable/c/33bf23c9940dbd3a22aad7f0cda4c84ed5701847
https://git.kernel.org/stable/c/f36d200a80a3ca025532ed60dd1ac21b620e14ae
https://git.kernel.org/stable/c/bffc4cc334c5bb31ded54bc3cfd651735a3cb79e
https://git.kernel.org/stable/c/3c12466b6b7bf1e56f9b32c366a3d83d87afb4de

Timeline