Commit 6a2febec authored Jun 30, 2020 by Eric Dumazet Committed by David S. Miller Jun 30, 2020

tcp: md5: add missing memory barriers in tcp_md5_do_add()/tcp_md5_hash_key()



MD5 keys are read with RCU protection, and tcp_md5_do_add()
might update in-place a prior key.

Normally, typical RCU updates would allocate a new piece
of memory. In this case only key->key and key->keylen might
be updated, and we do not care if an incoming packet could
see the old key, the new one, or some intermediate value,
since changing the key on a live flow is known to be problematic
anyway.

We only want to make sure that in the case key->keylen
is changed, cpus in tcp_md5_hash_key() wont try to use
uninitialized data, or crash because key->keylen was
read twice to feed sg_init_one() and ahash_request_set_crypt()

Fixes: 9ea88a15 ("tcp: md5: check md5 signature without socket lock")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 28541f3d

net/ipv4/tcp.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -4033,10 +4033,13 @@ EXPORT_SYMBOL(tcp_md5_hash_skb_data);

		int tcp_md5_hash_key(struct tcp_md5sig_pool hp, const struct tcp_md5sig_key key)
		{
		u8 keylen = key->keylen;
		struct scatterlist sg;

		sg_init_one(&sg, key->key, key->keylen);
		ahash_request_set_crypt(hp->md5_req, &sg, NULL, key->keylen);
		smp_rmb(); /* paired with smp_wmb() in tcp_md5_do_add() */

		sg_init_one(&sg, key->key, keylen);
		ahash_request_set_crypt(hp->md5_req, &sg, NULL, keylen);
		return crypto_ahash_update(hp->md5_req);
		}
		EXPORT_SYMBOL(tcp_md5_hash_key);

net/ipv4/tcp_ipv4.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -1113,6 +1113,9 @@ int tcp_md5_do_add(struct sock sk, const union tcp_md5_addr addr,
		if (key) {
		/* Pre-existing entry - just update that one. */
		memcpy(key->key, newkey, newkeylen);

		smp_wmb(); /* pairs with smp_rmb() in tcp_md5_hash_key() */

		key->keylen = newkeylen;
		return 0;
		}

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