{ "data_version": "4.0", "data_type": "CVE", "data_format": "MITRE", "CVE_data_meta": { "ID": "CVE-2024-26960", "ASSIGNER": "cve@kernel.org", "STATE": "PUBLIC" }, "description": { "description_data": [ { "lang": "eng", "value": "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<-----\n\n__swap_entry_free() might be the last user and result in\n\"count == SWAP_HAS_CACHE\".\n\nswapoff->try_to_unuse() will stop as soon as soon as si->inuse_pages==0.\n\nSo the question is: could someone reclaim the folio and turn\nsi->inuse_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-> count == SWAP_HAS_CACHE\n[then, preempted in the hypervisor etc.]\n\nProcess 2 quits. Calls free_swap_and_cache().\n-> 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()->folio_free_swap()->delete_from_swap_cache()->\nput_swap_folio()->free_swap_slot()->swapcache_free_entries()->\nswap_entry_free()->swap_range_free()->\n...\nWRITE_ONCE(si->inuse_pages, si->inuse_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<-----" } ] }, "problemtype": { "problemtype_data": [ { "description": [ { "lang": "eng", "value": "n/a" } ] } ] }, "affects": { "vendor": { "vendor_data": [ { "vendor_name": "Linux", "product": { "product_data": [ { "product_name": "Linux", "version": { "version_data": [ { "version_affected": "<", "version_name": "7c00bafee87c", "version_value": "d85c11c97ecf" }, { "version_value": "not down converted", "x_cve_json_5_version_data": { "versions": [ { "version": "4.11", "status": "affected" }, { "version": "0", "lessThan": "4.11", "status": "unaffected", "versionType": "custom" }, { "version": "5.10.215", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "custom" }, { "version": "5.15.154", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "custom" }, { "version": "6.1.84", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "custom" }, { "version": "6.6.24", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "custom" }, { "version": "6.7.12", "lessThanOrEqual": "6.7.*", "status": "unaffected", "versionType": "custom" }, { "version": "6.8.3", "lessThanOrEqual": "6.8.*", "status": "unaffected", "versionType": "custom" }, { "version": "6.9", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ], "defaultStatus": "affected" } } ] } } ] } } ] } }, "references": { "reference_data": [ { "url": "https://git.kernel.org/stable/c/d85c11c97ecf92d47a4b29e3faca714dc1f18d0d", "refsource": "MISC", "name": "https://git.kernel.org/stable/c/d85c11c97ecf92d47a4b29e3faca714dc1f18d0d" }, { "url": "https://git.kernel.org/stable/c/2da5568ee222ce0541bfe446a07998f92ed1643e", "refsource": "MISC", "name": "https://git.kernel.org/stable/c/2da5568ee222ce0541bfe446a07998f92ed1643e" }, { "url": "https://git.kernel.org/stable/c/1ede7f1d7eed1738d1b9333fd1e152ccb450b86a", "refsource": "MISC", "name": "https://git.kernel.org/stable/c/1ede7f1d7eed1738d1b9333fd1e152ccb450b86a" }, { "url": "https://git.kernel.org/stable/c/0f98f6d2fb5fad00f8299b84b85b6bc1b6d7d19a", "refsource": "MISC", "name": "https://git.kernel.org/stable/c/0f98f6d2fb5fad00f8299b84b85b6bc1b6d7d19a" }, { "url": "https://git.kernel.org/stable/c/3ce4c4c653e4e478ecb15d3c88e690f12cbf6b39", "refsource": "MISC", "name": "https://git.kernel.org/stable/c/3ce4c4c653e4e478ecb15d3c88e690f12cbf6b39" }, { "url": "https://git.kernel.org/stable/c/363d17e7f7907c8e27a9e86968af0eaa2301787b", "refsource": "MISC", "name": "https://git.kernel.org/stable/c/363d17e7f7907c8e27a9e86968af0eaa2301787b" }, { "url": "https://git.kernel.org/stable/c/82b1c07a0af603e3c47b906c8e991dc96f01688e", "refsource": "MISC", "name": "https://git.kernel.org/stable/c/82b1c07a0af603e3c47b906c8e991dc96f01688e" }, { "url": "https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html", "refsource": "MISC", "name": "https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html" } ] }, "generator": { "engine": "bippy-a5840b7849dd" } }