smc: Use __sk_dst_get() and dst_dev_rcu() in smc_clc_prfx_match().

smc_clc_prfx_match() is called from smc_listen_work() and
not under RCU nor RTNL.

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

Let's use __sk_dst_get() and dst_dev_rcu().

Note that the returned value of smc_clc_prfx_match() is not
used in the caller.

Fixes: a046d57da19f ("smc: CLC handshake (incl. preparation steps)")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250916214758.650211-4-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/smc/smc_clc.c b/net/smc/smc_clc.c
index 976b2102bdfcd91a3898d7e81fad11714be57a51..09745baa10170077ca143feccdcff9d521448e5d 100644 (file)
--- a/net/smc/smc_clc.c
+++ b/net/smc/smc_clc.c
@@ -657,26 +657,26 @@ static int smc_clc_prfx_match6_rcu(struct net_device *dev,
 int smc_clc_prfx_match(struct socket *clcsock,
                       struct smc_clc_msg_proposal_prefix *prop)
 {
-       struct dst_entry *dst = sk_dst_get(clcsock->sk);
+       struct net_device *dev;
+       struct dst_entry *dst;
        int rc;
 
-       if (!dst) {
-               rc = -ENOTCONN;
-               goto out;
-       }
-       if (!dst->dev) {
+       rcu_read_lock();
+
+       dst = __sk_dst_get(clcsock->sk);
+       dev = dst ? dst_dev_rcu(dst) : NULL;
+       if (!dev) {
                rc = -ENODEV;
-               goto out_rel;
+               goto out;
        }
-       rcu_read_lock();
+
        if (!prop->ipv6_prefixes_cnt)
-               rc = smc_clc_prfx_match4_rcu(dst->dev, prop);
+               rc = smc_clc_prfx_match4_rcu(dev, prop);
        else
-               rc = smc_clc_prfx_match6_rcu(dst->dev, prop);
-       rcu_read_unlock();
-out_rel:
-       dst_release(dst);
+               rc = smc_clc_prfx_match6_rcu(dev, prop);
 out:
+       rcu_read_unlock();
+
        return rc;
 }