6.6-stable review patch. If anyone has any objections, please let me know.
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From: John Fastabend john.fastabend@gmail.com
[ Upstream commit 16b2f264983dc264c1560cc0170e760dec1bf54f ]
When sockets are added to a sockmap or sockhash we allocate and init a psock. Then update the proto ops with sock_map_init_proto the flow is
sock_hash_update_common sock_map_link psock = sock_map_psock_get_checked() <-returns existing psock sock_map_init_proto(sk, psock) <- updates sk_proto
If the socket is already in a map this results in the sock_map_init_proto being called multiple times on the same socket. We do this because when a socket is added to multiple maps this might result in a new set of BPF programs being attached to the socket requiring an updated ops struct.
This creates a rule where it must be safe to call psock_update_sk_prot multiple times. When we added a fix for UAF through unix sockets in patch 4dd9a38a753fc we broke this rule by adding a sock_hold in that path to ensure the sock is not released. The result is if a af_unix stream sock is placed in multiple maps it results in a memory leak because we call sock_hold multiple times with only a single sock_put on it.
Fixes: 8866730aed51 ("bpf, sockmap: af_unix stream sockets need to hold ref for pair sock") Reported-by: Xingwei Lee xrivendell7@gmail.com Signed-off-by: John Fastabend john.fastabend@gmail.com Signed-off-by: Martin KaFai Lau martin.lau@kernel.org Reviewed-by: Jakub Sitnicki jakub@cloudflare.com Link: https://lore.kernel.org/r/20231221232327.43678-2-john.fastabend@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/unix/unix_bpf.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/net/unix/unix_bpf.c b/net/unix/unix_bpf.c index 7ea7c3a0d0d0..bd84785bf8d6 100644 --- a/net/unix/unix_bpf.c +++ b/net/unix/unix_bpf.c @@ -161,15 +161,30 @@ int unix_stream_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool r { struct sock *sk_pair;
+ /* Restore does not decrement the sk_pair reference yet because we must + * keep the a reference to the socket until after an RCU grace period + * and any pending sends have completed. + */ if (restore) { sk->sk_write_space = psock->saved_write_space; sock_replace_proto(sk, psock->sk_proto); return 0; }
- sk_pair = unix_peer(sk); - sock_hold(sk_pair); - psock->sk_pair = sk_pair; + /* psock_update_sk_prot can be called multiple times if psock is + * added to multiple maps and/or slots in the same map. There is + * also an edge case where replacing a psock with itself can trigger + * an extra psock_update_sk_prot during the insert process. So it + * must be safe to do multiple calls. Here we need to ensure we don't + * increment the refcnt through sock_hold many times. There will only + * be a single matching destroy operation. + */ + if (!psock->sk_pair) { + sk_pair = unix_peer(sk); + sock_hold(sk_pair); + psock->sk_pair = sk_pair; + } + unix_stream_bpf_check_needs_rebuild(psock->sk_proto); sock_replace_proto(sk, &unix_stream_bpf_prot); return 0;