Messages in this thread Patch in this message | | | From | Eric Dumazet <> | Date | Tue, 30 Jun 2020 20:36:51 -0700 | Subject | Re: [regression] TCP_MD5SIG on established sockets |
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On Tue, Jun 30, 2020 at 7:59 PM Herbert Xu <herbert@gondor.apana.org.au> wrote: > > On Tue, Jun 30, 2020 at 07:30:43PM -0700, Eric Dumazet wrote: > > > > I made this clear in the changelog, do we want comments all over the places ? > > Do not get me wrong, we had this bug for years and suddenly this is a > > big deal... > > I thought you were adding a new pair of smp_rmb/smp_wmb. If they > already exist in the code then I agree it's not a big deal. But > adding a new pair of bogus smp_Xmb's is bad for maintenance. >
If I knew so many people were excited about TCP / MD5, I would have posted all my patches on lkml ;)
Without the smp_wmb() we would still need something to prevent KMSAN from detecting that we read uninitialized bytes, if key->keylen is increased. (initial content of key->key[] is garbage)
Something like this :
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index f111660453241692a17c881dd6dc2910a1236263..c3af8180c7049d5c4987bf5c67e4aff2ed6967c9 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -4033,11 +4033,9 @@ 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); return crypto_ahash_update(hp->md5_req); diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 99916fcc15ca0be12c2c133ff40516f79e6fdf7f..0d08e0134335a21d23702e6a5c24a0f2b3c61c6f 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1114,9 +1114,13 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr, /* Pre-existing entry - just update that one. */ 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; }
@@ -1132,7 +1136,7 @@ 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()) {
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