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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: 9ea88a1530 ("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>
This commit is contained in:
Eric Dumazet 2020-06-30 16:41:01 -07:00 committed by David S. Miller
parent 28541f3d32
commit 6a2febec33
2 changed files with 8 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
net/ipv4/tcp.c
View File

@ -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);

3
net/ipv4/tcp_ipv4.c
View File

@ -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;
}