netdev - [PATCH net-next] tcp: Remove unnecessary null check in tcp_inbound_md5

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Message-ID: <20251022221209.19716-1-ebiggers@kernel.org>
Date: Wed, 22 Oct 2025 15:12:09 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: netdev@...r.kernel.org
Cc: Eric Dumazet <edumazet@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	"David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	David Ahern <dsahern@...nel.org>,
	Dmitry Safonov <0x7f454c46@...il.com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Eric Biggers <ebiggers@...nel.org>
Subject: [PATCH net-next] 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@...nel.org>
---
 net/ipv4/tcp.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e15b38f6bd2d5..b79da6d393927 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4884,22 +4884,20 @@ static enum skb_drop_reason
 tcp_inbound_md5_hash(const struct sock *sk, const struct sk_buff *skb,
 		     const void *saddr, const void *daddr,
 		     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;
 	}
 

base-commit: 962ac5ca99a5c3e7469215bf47572440402dfd59
-- 
2.51.0