In the Linux kernel, the following vulnerability has been resolved: bpf: Fix potential UAF in bpf_netns_link_update_prog In bpf_netns_link

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.