[PATCH net] rds: fix transport reference leak on rds_add_bound() failure

[Henry Martin <bsdhenrymartin@gmail.com>]

rds_bind() takes a module reference on the chosen transport via
rds_trans_get_preferred().  If the subsequent rds_add_bound() fails,
rs->rs_transport is reset to NULL without dropping the reference,
and rds_release_sock() later only calls rds_trans_put() when
rs_transport is non-NULL.

Every failed bind therefore leaks one rds_tcp module reference,
unprivileged and unbounded: a few hundred failed binds (e.g. to
port 1) make "rmmod rds_tcp" permanently impossible.  The reference
was originally balanced because the failed bind left rs_transport
in place for the release path; commit 05733434ee9a ("net/rds: Check
laddr_check before calling it") added the NULL-out without the
matching put.

Drop the reference in the failure branch; rds_trans_put() already
tolerates NULL.  The symmetric SO_RDS_TRANSPORT leak is covered by
the same fix.

This issue was discovered by Tencent CodeBuddy Security.

Cc: stable@vger.kernel.org
Fixes: 05733434ee9a ("net/rds: Check laddr_check before calling it")
Signed-off-by: Henry Martin <bsdhenrymartin@gmail.com>
---
 net/rds/bind.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/rds/bind.c b/net/rds/bind.c
index f800d920d9690..e4667b3128940 100644
--- a/net/rds/bind.c
+++ b/net/rds/bind.c
@@ -264,8 +264,10 @@ int rds_bind(struct socket *sock, struct sockaddr_unsized *uaddr, int addr_len)
 
 	sock_set_flag(sk, SOCK_RCU_FREE);
 	ret = rds_add_bound(rs, binding_addr, &port, scope_id);
-	if (ret)
+	if (ret) {
+		rds_trans_put(rs->rs_transport);
 		rs->rs_transport = NULL;
+	}
 
 out:
 	release_sock(sk);
-- 
2.43.7