From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ 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@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Acked-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
@@ -3394,13 +3394,13 @@ 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
@@ -995,12 +995,18 @@ int tcp_md5_do_add(struct sock *sk, cons
key = tcp_md5_do_lookup_exact(sk, addr, family, prefixlen);
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;
}
@@ -1016,7 +1022,7 @@ 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()) {
