mm, swap: fix SWAP_USAGE_OFFLIST_BIT collision with real usage count
- 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- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean?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 6.18.54, 7.2.8
- 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: mm, swap: fix SWAP_USAGE_OFFLIST_BIT collision with real usage count SWAP_USAGE_OFFLIST_BIT is embedded in the si->inuse_pages usage counter, and is meant to sit above any value that counter can reach. However, it is defined from BITS_PER_TYPE(atomic_t), so it is bit 30. On a system with 4 KiB pages the flag collides with the usage count once that count reaches 4 TiB. swap_usage_in_pages() masks bit 30 out, so whenever the real count has that bit set, every caller of it reads 4 TiB low: • /proc/swaps understates Used by 4 TiB. • A raw count of exactly 2^30 masks to zero, so try_to_unuse() takes its "if (!swap_usage_in_pages(si)) goto success;" early exit and swapoff tears the device down while pages are still swapped out. Nothing in the rest of swapoff aborts the teardown, so those pages are lost. Independently of swapoff, the collision also corrupts the counter and the plist. On a device in normal use, a free that leaves bit 30 set in the count makes swap_usage_sub() see the flag where there is only count, and call add_to_avail_list(). It clears the bit with fetch_and(~SWAP_USAGE_OFFLIST_BIT), leaving the stored count 4 TiB below the real one, and calls plist_add() on a device that is already listed, tripping the WARN_ON(!plist_node_empty(node)) in plist_add() and linking the node a second time. Change the definition of SWAP_USAGE_OFFLIST_BIT to be based on atomic_long_t instead. Note that the usage counter field itself is of this same type, so it is still a valid bit.
Timeline
- CVE published
- Record last updated
Affected versions
- Linux Linux
From b228386cf237e659cdf5d8037a19db0b0a06f6b5 · fixed in 0a41a46859df0d2bd7ed127197aac7c7389c00ed; From b228386cf237e659cdf5d8037a19db0b0a06f6b5 · fixed in 7c0d0d6de46076b43a2acaf1026b6648f8434c39; From b228386cf237e659cdf5d8037a19db0b0a06f6b5 · fixed in 12e9ac7bc5b254048f886bf421e3a15491106c1f
- Linux Linux
6.14
- KernelLinux
From 6.14.0 · fixed in 6.18.54; From 6.19.0 · fixed in 7.2.8