CVE-2026-90393

In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix potential UAF in bpf_netns_link_update_prog

In bpf_netns_link_update_prog, the checks for old_prog and prog type

are currently performed locklessly before acquiring netns_bpf_mutex.

This creates a race condition that can lead to a UAF issue.

If two threads concurrently execute BPF_LINK_UPDATE on the same netns

link, the following execution path can trigger a UAF:

CPU0 CPU1

bpf_netns_link_update_prog

if (old_prog && old_prog != link->prog)

return -EPERM;

bpf_netns_link_update_prog

if (old_prog && old_prog != link->prog)

...

old_prog = xchg(&link->prog, new_prog);

bpf_prog_put(old_prog);

if (new_prog->type != link->prog->type) <-- trigger UAF

Fix this by moving the old_prog and prog->type checks inside the

netns_bpf_mutex critical section. Meanwhile, use guard() to simplify

lock management and avoid all the goto jumping.