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bpf: sockmap missing NULL psock check

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Add psock NULL check to handle a racing sock event that can get the
sk_callback_lock before this case but after xchg happens causing the
refcnt to hit zero and sock user data (psock) to be null and queued
for garbage collection.

Also add a comment in the code because this is a bit subtle and
not obvious in my opinion.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
John Fastabend 2018-01-04 20:02:09 -08:00 committed by Daniel Borkmann
parent 5133550296
commit 5731a879d0
1 changed files with 9 additions and 2 deletions
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11
kernel/bpf/sockmap.c
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@ -591,8 +591,15 @@ static void sock_map_free(struct bpf_map *map)
write_lock_bh(&sock->sk_callback_lock);
psock = smap_psock_sk(sock);
smap_list_remove(psock, &stab->sock_map[i]);
smap_release_sock(psock, sock);
/* This check handles a racing sock event that can get the
* sk_callback_lock before this case but after xchg happens
* causing the refcnt to hit zero and sock user data (psock)
* to be null and queued for garbage collection.
*/
if (likely(psock)) {
smap_list_remove(psock, &stab->sock_map[i]);
smap_release_sock(psock, sock);
}
write_unlock_bh(&sock->sk_callback_lock);
}
rcu_read_unlock();