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Subject[PATCH AUTOSEL for 4.14 093/110] bpf: sockmap missing NULL psock check
Date
From: John Fastabend <john.fastabend@gmail.com>

[ Upstream commit 5731a879d03bdaa00265f8ebc32dfd0e65d25276 ]

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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
kernel/bpf/sockmap.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index dbd7b322a86b..1890be7ea9cd 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -588,8 +588,15 @@ 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();
--
2.11.0
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