CVE-2026-74363bpf: fix UAF by restoring RCU-delayed inode freeing in bpffs

Official description

In the Linux kernel, the following vulnerability has been resolved: bpf: fix UAF by restoring RCU-delayed inode freeing in bpffs commit 4f375ade6aa9 ("bpf: Avoid RCU context warning when unpinning htab with internal structs") moved inode cleanup from ->free_inode() into ->destroy_inode() to avoid sleeping in RCU context when calling bpf_any_put(). However this removed the RCU delay on freeing the inode itself and the cached symlink body (i_link), both of which can be accessed by RCU pathwalk (pick_link, may_lookup etc.). This causes a use-after-free when a concurrent unlinkat() drops the last inode reference and destroy_inode() frees the inode immediately, while another task is still walking the path in RCU mode and reads inode->i_opflags (offset +2) inside current_time() -> is_mgtime(). KASAN reports: BUG: KASAN: slab-use-after-free in is_mgtime include/linux/fs.h:2313 Read of size 2 at addr ffff8880407e4282 (offset +2 = i_opflags) The rules (per Al Viro): ->destroy_inode() called immediately, can sleep, use for blocking cleanup e.g. bpf_any_put() ->free_inode() called after RCU grace period, use for freeing inode and anything RCU-accessible e.g. i_link Fix: split the two concerns properly: - keep bpf_any_put() in bpf_destroy_inode() since it is blocking and needs to run promptly - introduce bpf_free_inode() to handle kfree(i_link) and free_inode_nonrcu() with proper RCU delay, preventing the UAF

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ea1c243c39e32b7fc1c2edfe32081ff7e30a877c
• https://git.kernel.org/stable/c/5fecb71c10c28aef276ba49c718dc961745fdcf0
• https://git.kernel.org/stable/c/c70d0f9114c3cc156f6029a400c4eb7e6f7c82b2
• https://git.kernel.org/stable/c/53649846e0437d1d9b7cb993cfe54c367addf7ae
• https://git.kernel.org/stable/c/61f19729728243c82476dee31315143ed3275e7f
• https://git.kernel.org/stable/c/0497ff765746d9b2d17445c8f7cc737b36c0152a
• https://git.kernel.org/stable/c/b93c55b4932dd7e32dca8cf34a3443cc87a02906