6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: John Fastabend <john.fastabend@xxxxxxxxx>
[ 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@xxxxxxxxx>
Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx>
Signed-off-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
Reviewed-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20231221232327.43678-2-john.fastabend@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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;
--
2.43.0
