CVE-2024-56549 (GCVE-0-2024-56549)
Vulnerability from cvelistv5
Published
2024-12-27 14:11
Modified
2026-08-05 11:44
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: cachefiles: Fix NULL pointer dereference in object->file At present, the object->file has the NULL pointer dereference problem in ondemand-mode. The root cause is that the allocated fd and object->file lifetime are inconsistent, and the user-space invocation to anon_fd uses object->file. Following is the process that triggers the issue: [write fd] [umount] cachefiles_ondemand_fd_write_iter fscache_cookie_state_machine cachefiles_withdraw_cookie if (!file) return -ENOBUFS cachefiles_clean_up_object cachefiles_unmark_inode_in_use fput(object->file) object->file = NULL // file NULL pointer dereference! __cachefiles_write(..., file, ...) Fix this issue by add an additional reference count to the object->file before write/llseek, and decrement after it finished.
References
Impacted products
Vendor Product Version
Linux Linux Version: c8383054506c77b814489c09877b5db83fd4abf2
Version: c8383054506c77b814489c09877b5db83fd4abf2
Version: c8383054506c77b814489c09877b5db83fd4abf2
Version: c8383054506c77b814489c09877b5db83fd4abf2
Version: c8383054506c77b814489c09877b5db83fd4abf2
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ncachefiles: Fix NULL pointer dereference in object-\u003efile\n\nAt present, the object-\u003efile has the NULL pointer dereference problem in\nondemand-mode. The root cause is that the allocated fd and object-\u003efile\nlifetime are inconsistent, and the user-space invocation to anon_fd uses\nobject-\u003efile. Following is the process that triggers the issue:\n\n\t  [write fd]\t\t\t\t[umount]\ncachefiles_ondemand_fd_write_iter\n\t\t\t\t       fscache_cookie_state_machine\n\t\t\t\t\t cachefiles_withdraw_cookie\n  if (!file) return -ENOBUFS\n\t\t\t\t\t   cachefiles_clean_up_object\n\t\t\t\t\t     cachefiles_unmark_inode_in_use\n\t\t\t\t\t     fput(object-\u003efile)\n\t\t\t\t\t     object-\u003efile = NULL\n  // file NULL pointer dereference!\n  __cachefiles_write(..., file, ...)\n\nFix this issue by add an additional reference count to the object-\u003efile\nbefore write/llseek, and decrement after it finished."
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              "value": "AV:L - The vulnerable code is reached through local file-descriptor operations (write()/lseek() on a cachefiles on-demand anon fd) raced against local cookie withdrawal (umount, LRU discard, invalidation). There is no remote or adjacent-network path into fs/cachefiles/ondemand.c.\nAC:L - The attacker controls both sides of the race \u2014 they generate the demand-read traffic that makes the daemon write on the anon fd, and they trigger the withdrawal (umount of their erofs-on-fscache mount, or letting the cookie idle past the ~2s LRU timeout) \u2014 and can retry the sequence indefinitely until the window is hit.\nPR:L - Although /dev/cachefiles itself requires CAP_SYS_ADMIN, an unprivileged local user of an on-demand erofs/fscache mount (e.g. inside a container using an on-demand image) drives both the daemon\u0027s writes and the cookie withdrawal without ever needing the anon fd, so basic unprivileged local access suffices.\nUI:N - No victim action is needed; the cachefiles daemon services demand-read requests automatically as part of normal operation, and the withdrawal path is driven by the attacker\u0027s own filesystem activity.\nS:U - The corruption is confined to kernel memory within the same security authority; this is standard kernel memory corruption, not a hypervisor, IOMMU, or sandbox boundary crossing.\nC:H - The use-after-free on struct file lets llseek/SEEK_DATA/SEEK_HOLE and DIO operations act on a freed slot that filp_cachep (SLAB_TYPESAFE_BY_RCU) hands out as an unrelated struct file, exposing freed-memory contents and redirecting reads to files the attacker has no access to.\nI:H - __cachefiles_write() calls get_file() and vfs_iocb_iter_write() on the dangling pointer, inflating a reallocated file\u0027s refcount (setting up a further UAF) and writing attacker-influenced cache data \u2014 plus fallocate() \u2014 into an unrelated open file, giving a controlled write primitive.\nA:H - Dereferencing the freed/NULLed object-\u003efile causes a kernel oops or panic, and the refcount corruption on the reallocated struct file leads to further fatal memory corruption."
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          "url": "https://git.kernel.org/stable/c/31ad74b20227ce6b40910ff78b1c604e42975cf1"
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      "title": "cachefiles: Fix NULL pointer dereference in object-\u003efile",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2024-56549",
    "datePublished": "2024-12-27T14:11:30.336Z",
    "dateReserved": "2024-12-27T14:03:05.989Z",
    "dateUpdated": "2026-08-05T11:44:58.475Z",
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