CVE-2023-52497 Information

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 ep 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.

Reference

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