[PATCH 5.15.y 2/2] net/smc: fix use-after-free in smc_rx_pipe_buf_release()

[Sasha Levin <sashal@kernel.org>]

From: Hidayath Khan <hidayath@linux.ibm.com>

[ Upstream commit c924884743e948e25625b7fbf3ee2a9325a204a7 ]

smc_rx_splice() hands RMB pages to a pipe and takes a socket reference
per entry so the smc_sock stays alive until the reader finishes. The
connection does not: a concurrent close runs smc_conn_free(), which
releases the receive buffer back to the link group pool.

smc_rx_pipe_buf_release() tests sk_state before taking the socket lock.
The state can change between the test and the lock, and
smc_rx_update_cons() then dereferences conn->rmb_desc and walks
conn->lgr, which smc_conn_free() has already released. On the
is_reg_err path smcr_buf_unuse() frees the descriptor outright, so
this is a use-after-free.

Take the socket lock first and test conn->freed instead.
smc_conn_free() sets that flag before releasing anything, and every
caller holds the socket lock. The two paths exclude each other: either
the pipe release runs first with everything valid, or it sees the flag
and skips the update.

Fixes: 9014db202cb7 ("smc: add support for splice()")
Cc: stable@vger.kernel.org
Reviewed-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Signed-off-by: Hidayath Khan <hidayath@linux.ibm.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260820074642.966856-3-hidayath@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/smc/smc_rx.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/net/smc/smc_rx.c b/net/smc/smc_rx.c
index 33b5bcafdec7d..318ffb372f384 100644
--- a/net/smc/smc_rx.c
+++ b/net/smc/smc_rx.c
@@ -110,16 +110,15 @@ static void smc_rx_pipe_buf_release(struct pipe_inode_info *pipe,
 				    struct pipe_buffer *buf)
 {
 	struct smc_spd_priv *priv = (struct smc_spd_priv *)buf->private;
+	struct smc_connection *conn = &priv->smc->conn;
 	struct smc_sock *smc = priv->smc;
-	struct smc_connection *conn;
 	struct sock *sk = &smc->sk;
 
-	if (sk->sk_state == SMC_CLOSED ||
-	    sk->sk_state == SMC_PEERFINCLOSEWAIT ||
-	    sk->sk_state == SMC_APPFINCLOSEWAIT)
-		goto out;
-	conn = &smc->conn;
 	lock_sock(sk);
+	if (conn->freed) {
+		release_sock(sk);
+		goto out;
+	}
 	smc_rx_update_cons(smc, priv->len);
 	release_sock(sk);
 	if (atomic_sub_and_test(priv->len, &conn->splice_pending))
-- 
2.53.0