In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mm, swap: fix SWAP_USAGE_OFFLIST_BIT collision with real usage count<\/p>\n
SWAP_USAGE_OFFLIST_BIT is embedded in the si->inuse_pages usage counter,
\nand is meant to sit above any value that counter can reach. However, it
\nis defined from BITS_PER_TYPE(atomic_t), so it is bit 30. On a system
\nwith 4 KiB pages the flag collides with the usage count once that count
\nreaches 4 TiB.<\/p>\n
swap_usage_in_pages() masks bit 30 out, so whenever the real count has
\nthat bit set, every caller of it reads 4 TiB low:<\/p>\n
* \/proc\/swaps understates Used by 4 TiB.<\/p>\n
* A raw count of exactly 2^30 masks to zero, so try_to_unuse() takes its
\n “if (!swap_usage_in_pages(si)) goto success;” early exit and swapoff
\n tears the device down while pages are still swapped out. Nothing in
\n the rest of swapoff aborts the teardown, so those pages are lost.<\/p>\n
Independently of swapoff, the collision also corrupts the counter and the
\nplist. On a device in normal use, a free that leaves bit 30 set in the
\ncount makes swap_usage_sub() see the flag where there is only count, and
\ncall add_to_avail_list(). It clears the bit with
\nfetch_and(~SWAP_USAGE_OFFLIST_BIT), leaving the stored count 4 TiB below
\nthe real one, and calls plist_add() on a device that is already listed,
\ntripping the WARN_ON(!plist_node_empty(node)) in plist_add() and linking
\nthe node a second time.<\/p>\n
Change the definition of SWAP_USAGE_OFFLIST_BIT to be based on
\natomic_long_t instead. Note that the usage counter field itself is of
\nthis same type, so it is still a valid bit.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mm, swap: fix SWAP_USAGE_OFFLIST_BIT collision with real usage count<\/p>\n
SWAP_USAGE_OFFLIST_BIT is embedded in the si->inuse_pages usa<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-33295","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/33295","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=33295"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=33295"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=33295"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}