From: Eric Dumazet edumazet@google.com
[ Upstream commit e6ced831ef11a2a06e8d00aad9d4fc05b610bf38 ]
My prior fix went a bit too far, according to Herbert and Mathieu.
Since we accept that concurrent TCP MD5 lookups might see inconsistent keys, we can use READ_ONCE()/WRITE_ONCE() instead of smp_rmb()/smp_wmb()
Clearing all key->key[] is needed to avoid possible KMSAN reports, if key->keylen is increased. Since tcp_md5_do_add() is not fast path, using __GFP_ZERO to clear all struct tcp_md5sig_key is simpler.
data_race() was added in linux-5.8 and will prevent KCSAN reports, this can safely be removed in stable backports, if data_race() is not yet backported.
v2: use data_race() both in tcp_md5_hash_key() and tcp_md5_do_add()
Fixes: 6a2febec338d ("tcp: md5: add missing memory barriers in tcp_md5_do_add()/tcp_md5_hash_key()") Signed-off-by: Eric Dumazet edumazet@google.com Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Herbert Xu herbert@gondor.apana.org.au Cc: Marco Elver elver@google.com Reviewed-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Acked-by: Herbert Xu herbert@gondor.apana.org.au Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp.c | 6 +++--- net/ipv4/tcp_ipv4.c | 14 ++++++++++---- 2 files changed, 13 insertions(+), 7 deletions(-)
--- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3880,13 +3880,13 @@ 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; + u8 keylen = READ_ONCE(key->keylen); /* paired with WRITE_ONCE() in tcp_md5_do_add */ struct scatterlist sg;
- 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); + + /* tcp_md5_do_add() might change key->key under us */ return crypto_ahash_update(hp->md5_req); } EXPORT_SYMBOL(tcp_md5_hash_key); --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1103,12 +1103,18 @@ int tcp_md5_do_add(struct sock *sk, cons
key = tcp_md5_do_lookup_exact(sk, addr, family, prefixlen, l3index); if (key) { - /* Pre-existing entry - just update that one. */ + /* Pre-existing entry - just update that one. + * Note that the key might be used concurrently. + */ memcpy(key->key, newkey, newkeylen);
- smp_wmb(); /* pairs with smp_rmb() in tcp_md5_hash_key() */ + /* Pairs with READ_ONCE() in tcp_md5_hash_key(). + * Also note that a reader could catch new key->keylen value + * but old key->key[], this is the reason we use __GFP_ZERO + * at sock_kmalloc() time below these lines. + */ + WRITE_ONCE(key->keylen, newkeylen);
- key->keylen = newkeylen; return 0; }
@@ -1124,7 +1130,7 @@ int tcp_md5_do_add(struct sock *sk, cons rcu_assign_pointer(tp->md5sig_info, md5sig); }
- key = sock_kmalloc(sk, sizeof(*key), gfp); + key = sock_kmalloc(sk, sizeof(*key), gfp | __GFP_ZERO); if (!key) return -ENOMEM; if (!tcp_alloc_md5sig_pool()) {