smc_clc_prfx_set() is called during connect() and not under RCU
nor RTNL.

Using sk_dst_get(sk)->dev could trigger UAF.

Let's use sk_dst_get_rcu() under rcu_read_lock() after
kernel_getsockname().

While at it, we change the 1st arg of smc_clc_prfx_set[46]_rcu()
not to touch dst there.

Fixes: a046d57da19f ("smc: CLC handshake (incl. preparation steps)")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
Cc: "D. Wythe" <alibuda@linux.alibaba.com>
Cc: Dust Li <dust.li@linux.alibaba.com>
Cc: Sidraya Jayagond <sidraya@linux.ibm.com>
Cc: Wenjia Zhang <wenjia@linux.ibm.com>
Cc: Mahanta Jambigi <mjambigi@linux.ibm.com>
Cc: Tony Lu <tonylu@linux.alibaba.com>
Cc: Wen Gu <guwen@linux.alibaba.com>
Cc: Ursula Braun <ubraun@linux.vnet.ibm.com>
---
 net/smc/smc_clc.c | 39 ++++++++++++++++++++-------------------
 1 file changed, 20 insertions(+), 19 deletions(-)

diff --git a/net/smc/smc_clc.c b/net/smc/smc_clc.c
index 08be56dfb3f2..9aa1d75d3079 100644
--- a/net/smc/smc_clc.c
+++ b/net/smc/smc_clc.c
@@ -509,10 +509,10 @@ static bool smc_clc_msg_hdr_valid(struct smc_clc_msg_hdr *clcm, bool check_trl)
 }
 
 /* find ipv4 addr on device and get the prefix len, fill CLC proposal msg */
-static int smc_clc_prfx_set4_rcu(struct dst_entry *dst, __be32 ipv4,
+static int smc_clc_prfx_set4_rcu(struct net_device *dev, __be32 ipv4,
 				 struct smc_clc_msg_proposal_prefix *prop)
 {
-	struct in_device *in_dev = __in_dev_get_rcu(dst->dev);
+	struct in_device *in_dev = __in_dev_get_rcu(dev);
 	const struct in_ifaddr *ifa;
 
 	if (!in_dev)
@@ -530,12 +530,12 @@ static int smc_clc_prfx_set4_rcu(struct dst_entry *dst, __be32 ipv4,
 }
 
 /* fill CLC proposal msg with ipv6 prefixes from device */
-static int smc_clc_prfx_set6_rcu(struct dst_entry *dst,
+static int smc_clc_prfx_set6_rcu(struct net_device *dev,
 				 struct smc_clc_msg_proposal_prefix *prop,
 				 struct smc_clc_ipv6_prefix *ipv6_prfx)
 {
 #if IS_ENABLED(CONFIG_IPV6)
-	struct inet6_dev *in6_dev = __in6_dev_get(dst->dev);
+	struct inet6_dev *in6_dev = __in6_dev_get(dev);
 	struct inet6_ifaddr *ifa;
 	int cnt = 0;
 
@@ -564,41 +564,42 @@ static int smc_clc_prfx_set(struct socket *clcsock,
 			    struct smc_clc_msg_proposal_prefix *prop,
 			    struct smc_clc_ipv6_prefix *ipv6_prfx)
 {
-	struct dst_entry *dst = sk_dst_get(clcsock->sk);
 	struct sockaddr_storage addrs;
 	struct sockaddr_in6 *addr6;
 	struct sockaddr_in *addr;
+	struct net_device *dev;
 	int rc = -ENOENT;
 
-	if (!dst) {
-		rc = -ENOTCONN;
-		goto out;
-	}
-	if (!dst->dev) {
-		rc = -ENODEV;
-		goto out_rel;
-	}
 	/* get address to which the internal TCP socket is bound */
 	if (kernel_getsockname(clcsock, (struct sockaddr *)&addrs) < 0)
-		goto out_rel;
+		goto out;
+
 	/* analyze IP specific data of net_device belonging to TCP socket */
 	addr6 = (struct sockaddr_in6 *)&addrs;
+
 	rcu_read_lock();
+
+	dev = sk_dst_dev_rcu(clcsock->sk);
+	if (!dev) {
+		rc = -ENODEV;
+		goto out_unlock;
+	}
+
 	if (addrs.ss_family == PF_INET) {
 		/* IPv4 */
 		addr = (struct sockaddr_in *)&addrs;
-		rc = smc_clc_prfx_set4_rcu(dst, addr->sin_addr.s_addr, prop);
+		rc = smc_clc_prfx_set4_rcu(dev, addr->sin_addr.s_addr, prop);
 	} else if (ipv6_addr_v4mapped(&addr6->sin6_addr)) {
 		/* mapped IPv4 address - peer is IPv4 only */
-		rc = smc_clc_prfx_set4_rcu(dst, addr6->sin6_addr.s6_addr32[3],
+		rc = smc_clc_prfx_set4_rcu(dev, addr6->sin6_addr.s6_addr32[3],
 					   prop);
 	} else {
 		/* IPv6 */
-		rc = smc_clc_prfx_set6_rcu(dst, prop, ipv6_prfx);
+		rc = smc_clc_prfx_set6_rcu(dev, prop, ipv6_prfx);
 	}
+
+out_unlock:
 	rcu_read_unlock();
-out_rel:
-	dst_release(dst);
 out:
 	return rc;
 }
-- 
2.51.0.384.g4c02a37b29-goog