erofs: disable LZ4 rolling decompression for now
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Fix
- Fixed in 6.6.160, 6.12.114, 6.18.53, 7.2.7
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
In the Linux kernel, the following vulnerability has been resolved: erofs: disable LZ4 rolling decompression for now LZ4 rolling decompression [1] was introduced to reduce the memory footprint of temporary pages: For many cases, it is needed for users to read small data within a compressed extent (pcluster), either due to random small read, or since uptodate folios (typically order-0) cannot be reused for decompression again since decompression algorithm refills already-uptodate folios. Rolling decompression works because LZ4 is LZ77-based and only refers to the most recent 64 KiB of decompressed data, so in theory only a bounded rolling window of temporary pages is needed when decompressing. It can save a lot of temporary memory, e.g. 601,960-byte data can be compressed into a 256k LZ4 compressed extent, which means it needs 146 extra pages per request in the worst case if rolling decompression is disabled. However, the upstream LZ4 implementation is not under EROFS' control: For example, the literal copy memmove() may still **copy long literals backward** on x86 based on the address comparison even when the source and destination ranges do not overlap (IOWs, inline decompression doesn't need to be considered here). That breaks the rolling assumption and makes the optimization broken. Disable it for now to make sure the data correctness first since EROFS is used everywhere now: The rolling window approach can be revived once we either ensure that the official LZ4 code always copies forward for non-overlapping ranges or maintain our own LZ4 implementation in EROFS. The main impact is a higher runtime memory footprint; However, recent commit 0f6273ab4637 ("erofs: add a reserved buffer pool for lz4 decompression") helps mitigate this when enabled but it's still not perfect. [1] https://www.usenix.org/conference/atc19/presentation/gao § 3.3 Decompression
Timeline
- CVE published
- Record last updated
Affected versions
- Linux Linux
From 8e6c8fa9f2e95c88a642521a5da19a8e31748846 · fixed in dcc5e6c9e4d06fe73fc61e730ee3e51dd115a4d8; From 8e6c8fa9f2e95c88a642521a5da19a8e31748846 · fixed in d923e53472b468a50a6cf41341531d5170c68371; From 8e6c8fa9f2e95c88a642521a5da19a8e31748846 · fixed in ec52dfed7b14514ed97ee71161e4cf4cfe2fbff2; From 8e6c8fa9f2e95c88a642521a5da19a8e31748846 · fixed in c9a2db4b9950b59c571258e4bae74c271f62dd66; From 8e6c8fa9f2e95c88a642521a5da19a8e31748846 · fixed in 82e664cf1219c459c33aae931b222cf951af9cb7
- Linux Linux
5.13
- KernelLinux
From 5.13.0 · fixed in 6.6.160; From 6.7.0 · fixed in 6.12.114; From 6.13.0 · fixed in 6.18.53; From 6.19.0 · fixed in 7.2.7