CVE-2024-56549 – Linux Kernel cachefiles NULL Pointer Dereference

CVE ID : CVE-2024-56549

Published : Dec. 27, 2024, 2:15 p.m. | 1 hour ago

Description : 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.

Severity: 0.0 | NA

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CVE-2024-56549 – Linux Kernel cachefiles NULL Pointer Dereference