tcp: Remove unnecessary null check in tcp_inbound_md5_hash()

The 'if (!key && hash_location)' check in tcp_inbound_md5_hash() implies
that hash_location might be null.  However, later code in the function
dereferences hash_location anyway, without checking for null first.
Fortunately, there is no real bug, since tcp_inbound_md5_hash() is
called only with non-null values of hash_location.

Therefore, remove the unnecessary and misleading null check of
hash_location.  This silences a Smatch static checker warning
(https://lore.kernel.org/netdev/aPi4b6aWBbBR52P1@stanley.mountain/)

Also fix the related comment at the beginning of the function.

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Link: https://patch.msgid.link/20251022221209.19716-1-ebiggers@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e15b38f6bd2d5c375dad47b8221897915ddab24b..b79da6d39392751e189f1f65969b15c904a6792a 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4886,18 +4886,16 @@ tcp_inbound_md5_hash(const struct sock *sk, const struct sk_buff *skb,
                     int family, int l3index, const __u8 *hash_location)
 {
        /* This gets called for each TCP segment that has TCP-MD5 option.
-        * We have 3 drop cases:
-        * o No MD5 hash and one expected.
-        * o MD5 hash and we're not expecting one.
-        * o MD5 hash and its wrong.
+        * We have 2 drop cases:
+        * o An MD5 signature is present, but we're not expecting one.
+        * o The MD5 signature is wrong.
         */
        const struct tcp_sock *tp = tcp_sk(sk);
        struct tcp_md5sig_key *key;
        u8 newhash[16];
 
        key = tcp_md5_do_lookup(sk, l3index, saddr, family);
-
-       if (!key && hash_location) {
+       if (!key) {
                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5UNEXPECTED);
                trace_tcp_hash_md5_unexpected(sk, skb);
                return SKB_DROP_REASON_TCP_MD5UNEXPECTED;