{ "schema_version": "1.6.1", "id": "RPI-CVE-2024-45000", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2024-45000" ], "published": "2024-09-04T19:57:01Z", "summary": "fs/netfs/fscache_cookie: add missing \"n_accesses\" check", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs/netfs/fscache_cookie: add missing \"n_accesses\" check\n\nThis fixes a NULL pointer dereference bug due to a data race which\nlooks like this:\n\n BUG: kernel NULL pointer dereference, address: 0000000000000008\n #PF: supervisor read access in kernel mode\n #PF: error_code(0x0000) - not-present page\n PGD 0 P4D 0\n Oops: 0000 [#1] SMP PTI\n CPU: 33 PID: 16573 Comm: kworker/u97:799 Not tainted 6.8.7-cm4all1-hp+ #43\n Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 10/17/2018\n Workqueue: events_unbound netfs_rreq_write_to_cache_work\n RIP: 0010:cachefiles_prepare_write+0x30/0xa0\n Code: 57 41 56 45 89 ce 41 55 49 89 cd 41 54 49 89 d4 55 53 48 89 fb 48 83 ec 08 48 8b 47 08 48 83 7f 10 00 48 89 34 24 48 8b 68 20 <48> 8b 45 08 4c 8b 38 74 45 49 8b 7f 50 e8 4e a9 b0 ff 48 8b 73 10\n RSP: 0018:ffffb4e78113bde0 EFLAGS: 00010286\n RAX: ffff976126be6d10 RBX: ffff97615cdb8438 RCX: 0000000000020000\n RDX: ffff97605e6c4c68 RSI: ffff97605e6c4c60 RDI: ffff97615cdb8438\n RBP: 0000000000000000 R08: 0000000000278333 R09: 0000000000000001\n R10: ffff97605e6c4600 R11: 0000000000000001 R12: ffff97605e6c4c68\n R13: 0000000000020000 R14: 0000000000000001 R15: ffff976064fe2c00\n FS: 0000000000000000(0000) GS:ffff9776dfd40000(0000) knlGS:0000000000000000\n CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n CR2: 0000000000000008 CR3: 000000005942c002 CR4: 00000000001706f0\n Call Trace:\n \n ? __die+0x1f/0x70\n ? page_fault_oops+0x15d/0x440\n ? search_module_extables+0xe/0x40\n ? fixup_exception+0x22/0x2f0\n ? exc_page_fault+0x5f/0x100\n ? asm_exc_page_fault+0x22/0x30\n ? cachefiles_prepare_write+0x30/0xa0\n netfs_rreq_write_to_cache_work+0x135/0x2e0\n process_one_work+0x137/0x2c0\n worker_thread+0x2e9/0x400\n ? __pfx_worker_thread+0x10/0x10\n kthread+0xcc/0x100\n ? __pfx_kthread+0x10/0x10\n ret_from_fork+0x30/0x50\n ? __pfx_kthread+0x10/0x10\n ret_from_fork_asm+0x1b/0x30\n \n Modules linked in:\n CR2: 0000000000000008\n ---[ end trace 0000000000000000 ]---\n\nThis happened because fscache_cookie_state_machine() was slow and was\nstill running while another process invoked fscache_unuse_cookie();\nthis led to a fscache_cookie_lru_do_one() call, setting the\nFSCACHE_COOKIE_DO_LRU_DISCARD flag, which was picked up by\nfscache_cookie_state_machine(), withdrawing the cookie via\ncachefiles_withdraw_cookie(), clearing cookie->cache_priv.\n\nAt the same time, yet another process invoked\ncachefiles_prepare_write(), which found a NULL pointer in this code\nline:\n\n struct cachefiles_object *object = cachefiles_cres_object(cres);\n\nThe next line crashes, obviously:\n\n struct cachefiles_cache *cache = object->volume->cache;\n\nDuring cachefiles_prepare_write(), the \"n_accesses\" counter is\nnon-zero (via fscache_begin_operation()). The cookie must not be\nwithdrawn until it drops to zero.\n\nThe counter is checked by fscache_cookie_state_machine() before\nswitching to FSCACHE_COOKIE_STATE_RELINQUISHING and\nFSCACHE_COOKIE_STATE_WITHDRAWING (in \"case\nFSCACHE_COOKIE_STATE_FAILED\"), but not for\nFSCACHE_COOKIE_STATE_LRU_DISCARDING (\"case\nFSCACHE_COOKIE_STATE_ACTIVE\").\n\nThis patch adds the missing check. With a non-zero access counter,\nthe function returns and the next fscache_end_cookie_access() call\nwill queue another fscache_cookie_state_machine() call to handle the\nstill-pending FSCACHE_COOKIE_DO_LRU_DISCARD.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.47-1+rpt4" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" } ] }, "database_specific": { "per_version": { "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.107", "compiled_filter": false } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2024-45000" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/b8a50877f68efdcc0be3fcc5116e00c31b90e45b" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/dfaa39b05a6cf34a16c525a2759ee6ab26b5fef6" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/0a4d41fa14b2a0efd40e350cfe8ec6a4c998ac1d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/f71aa06398aabc2e3eaac25acdf3d62e0094ba70" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T11:52:36Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.8, "cvss_v3_severity": "High", "scenario": "AV:L - The vulnerable path is reached through ordinary file I/O (open/read/close) on a locally mounted fscache-backed network filesystem or erofs-over-fscache image; no network packet processing initiates the operation, only local VFS activity does.\nAC:L - The attacker controls both sides of the race \u2014 the in-flight write-to-cache operation that holds n_accesses, and the close that puts the cookie on the LRU with a deterministic 10-second (10*HZ) discard timer \u2014 and can run it across thousands of files concurrently to widen the window and retry indefinitely.\nPR:L - Only an unprivileged local user with read access to files on the cached mount is required; no capability, no cachefilesd interaction, and no CAP_SYS_ADMIN is needed to drive cookie use/unuse and cache writeback.\nUI:N - No victim action is needed during the attack \u2014 the fsc-enabled mount is a pre-existing system configuration, and the attacker triggers everything itself via its own file I/O.\nS:U - The corruption and its consequences stay within the kernel's own security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - Premature withdrawal frees the cachefiles_object via kmem_cache_free with no RCU delay while cachefiles_prepare_write still dereferences it, so pointers (object->volume, ->cache, ->cookie, ->file) are read out of reclaimable slab memory, giving an attacker-groomable arbitrary-read primitive.\nI:H - The same use-after-free feeds a freed/reclaimed pointer into cachefiles_begin_secure() \u2192 override_creds(cache->cache_cred) and into refcount_inc via cachefiles_grab_object, plus writes through object->file in __cachefiles_prepare_write \u2014 a credential-substitution and write primitive exploitable for privilege escalation.\nA:H - The reported and easily reproduced outcome is a kernel NULL pointer dereference oops in the events_unbound worker (cachefiles_prepare_write+0x30), killing the workqueue thread and destabilizing the system; UAF outcomes crash equally." } } }