diff options
| author | Eric Dumazet <edumazet@google.com> | 2020-07-01 11:43:04 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-07-22 09:10:04 +0200 |
| commit | 190a385e7bfc387524772c6f99c28626775a5bb3 (patch) | |
| tree | f4e7b0b9bebe4dbe3d7695e4e69e4ee9fdac2c33 /net/ipv4 | |
| parent | 172671b46c16b49e7850cc0d511a57413f0aa518 (diff) | |
tcp: md5: refine tcp_md5_do_add()/tcp_md5_hash_key() barriers
[ 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>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/tcp.c | 6 | ||||
| -rw-r--r-- | net/ipv4/tcp_ipv4.c | 14 |
2 files changed, 13 insertions, 7 deletions
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index d9422dd9a865..bab9455621f6 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3088,12 +3088,12 @@ 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); + + /* tcp_md5_do_add() might change key->key under us */ return crypto_hash_update(&hp->md5_desc, &sg, key->keylen); } EXPORT_SYMBOL(tcp_md5_hash_key); diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 27c088ff1dad..3826745a160e 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -931,12 +931,18 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr, key = tcp_md5_do_lookup(sk, addr, family); 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; } @@ -953,7 +959,7 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr, 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()) { |