{"id":"CVE-2024-26960","summary":"mm: swap: fix race between free_swap_and_cache() and swapoff()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm: swap: fix race between free_swap_and_cache() and swapoff()\n\nThere was previously a theoretical window where swapoff() could run and\nteardown a swap_info_struct while a call to free_swap_and_cache() was\nrunning in another thread.  This could cause, amongst other bad\npossibilities, swap_page_trans_huge_swapped() (called by\nfree_swap_and_cache()) to access the freed memory for swap_map.\n\nThis is a theoretical problem and I haven't been able to provoke it from a\ntest case.  But there has been agreement based on code review that this is\npossible (see link below).\n\nFix it by using get_swap_device()/put_swap_device(), which will stall\nswapoff().  There was an extra check in _swap_info_get() to confirm that\nthe swap entry was not free.  This isn't present in get_swap_device()\nbecause it doesn't make sense in general due to the race between getting\nthe reference and swapoff.  So I've added an equivalent check directly in\nfree_swap_and_cache().\n\nDetails of how to provoke one possible issue (thanks to David Hildenbrand\nfor deriving this):\n\n--8\u003c-----\n\n__swap_entry_free() might be the last user and result in\n\"count == SWAP_HAS_CACHE\".\n\nswapoff-\u003etry_to_unuse() will stop as soon as soon as si-\u003einuse_pages==0.\n\nSo the question is: could someone reclaim the folio and turn\nsi-\u003einuse_pages==0, before we completed swap_page_trans_huge_swapped().\n\nImagine the following: 2 MiB folio in the swapcache. Only 2 subpages are\nstill references by swap entries.\n\nProcess 1 still references subpage 0 via swap entry.\nProcess 2 still references subpage 1 via swap entry.\n\nProcess 1 quits. Calls free_swap_and_cache().\n-\u003e count == SWAP_HAS_CACHE\n[then, preempted in the hypervisor etc.]\n\nProcess 2 quits. Calls free_swap_and_cache().\n-\u003e count == SWAP_HAS_CACHE\n\nProcess 2 goes ahead, passes swap_page_trans_huge_swapped(), and calls\n__try_to_reclaim_swap().\n\n__try_to_reclaim_swap()-\u003efolio_free_swap()-\u003edelete_from_swap_cache()-\u003e\nput_swap_folio()-\u003efree_swap_slot()-\u003eswapcache_free_entries()-\u003e\nswap_entry_free()-\u003eswap_range_free()-\u003e\n...\nWRITE_ONCE(si-\u003einuse_pages, si-\u003einuse_pages - nr_entries);\n\nWhat stops swapoff to succeed after process 2 reclaimed the swap cache\nbut before process1 finished its call to swap_page_trans_huge_swapped()?\n\n--8\u003c-----","modified":"2026-04-02T10:06:32.511856Z","published":"2024-05-01T05:19:12.112Z","related":["ALSA-2024:5101","SUSE-SU-2024:1644-1","SUSE-SU-2024:1659-1","SUSE-SU-2024:1663-1","SUSE-SU-2024:2135-1","SUSE-SU-2024:2203-1","SUSE-SU-2024:2973-1","SUSE-SU-2025:20008-1","SUSE-SU-2025:20028-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/26xxx/CVE-2024-26960.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/0f98f6d2fb5fad00f8299b84b85b6bc1b6d7d19a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/1ede7f1d7eed1738d1b9333fd1e152ccb450b86a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/2da5568ee222ce0541bfe446a07998f92ed1643e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/363d17e7f7907c8e27a9e86968af0eaa2301787b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3ce4c4c653e4e478ecb15d3c88e690f12cbf6b39"},{"type":"WEB","url":"https://git.kernel.org/stable/c/82b1c07a0af603e3c47b906c8e991dc96f01688e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d85c11c97ecf92d47a4b29e3faca714dc1f18d0d"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/26xxx/CVE-2024-26960.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-26960"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"7c00bafee87c7bac7ed9eced7c161f8e5332cb4e"},{"fixed":"d85c11c97ecf92d47a4b29e3faca714dc1f18d0d"},{"fixed":"2da5568ee222ce0541bfe446a07998f92ed1643e"},{"fixed":"1ede7f1d7eed1738d1b9333fd1e152ccb450b86a"},{"fixed":"0f98f6d2fb5fad00f8299b84b85b6bc1b6d7d19a"},{"fixed":"3ce4c4c653e4e478ecb15d3c88e690f12cbf6b39"},{"fixed":"363d17e7f7907c8e27a9e86968af0eaa2301787b"},{"fixed":"82b1c07a0af603e3c47b906c8e991dc96f01688e"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-26960.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}