Re: [PATCH net-next] net: Fix incorrect address comparison when searching for a bind2 bucket

From: Andrei Vagin <redacted>
Date: Fri, 8 Sep 2023 14:54:12 -0700

On Mon, Sep 26, 2022 at 05:25:44PM -0700, Martin KaFai Lau wrote:

quoted

From: Martin KaFai Lau <martin.lau@kernel.org>

The v6_rcv_saddr and rcv_saddr are inside a union in the
'struct inet_bind2_bucket'.  When searching a bucket by following the
bhash2 hashtable chain, eg. inet_bind2_bucket_match, it is only using
the sk->sk_family and there is no way to check if the inet_bind2_bucket
has a v6 or v4 address in the union.  This leads to an uninit-value
KMSAN report in [0] and also potentially incorrect matches.

This patch fixes it by adding a family member to the inet_bind2_bucket
and then tests 'sk->sk_family != tb->family' before matching
the sk's address to the tb's address.

It seems this patch doesn't handle v4mapped addresses properly. One of
gVisor test started failing with this change:

socket(AF_INET6, SOCK_STREAM, IPPROTO_IP) = 3
bind(3, {sa_family=AF_INET6, sin6_port=htons(0), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::ffff:0.0.0.0", &sin6_addr), sin6_scope_id=0}, 28) = 0
getsockname(3, {sa_family=AF_INET6, sin6_port=htons(33789), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::ffff:0.0.0.0", &sin6_addr), sin6_scope_id=0}, [28]) = 0
socket(AF_INET6, SOCK_STREAM, IPPROTO_IP) = 4
bind(4, {sa_family=AF_INET6, sin6_port=htons(33789), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_scope_id=0}, 28) = 0
socket(AF_INET, SOCK_STREAM, IPPROTO_IP) = 5
bind(5, {sa_family=AF_INET, sin_port=htons(33789), sin_addr=inet_addr("127.0.0.1")}, 16) = 0

The test expects that the second bind returns EADDRINUSE.

Thanks for the report.

inet_bind2_bucket_match_addr_any() forgot to take care of
IPV6_ADDR_MAPPED inaddr_any case.

This change fixes the regression.  I'll post a patch after
checking other two functions that the commit touched.

---8<---

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 7876b7d703cb..6f2a8dba24fe 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c

@@ -837,7 +837,9 @@ bool inet_bind2_bucket_match_addr_any(const struct inet_bind2_bucket *tb, const
 		if (sk->sk_family == AF_INET)
 			return net_eq(ib2_net(tb), net) && tb->port == port &&
 				tb->l3mdev == l3mdev &&
-				ipv6_addr_any(&tb->v6_rcv_saddr);
+				(ipv6_addr_any(&tb->v6_rcv_saddr) ||
+				 (ipv6_addr_type(&tb->v6_rcv_saddr) == IPV6_ADDR_MAPPED &&
+				  tb->v6_rcv_saddr.s6_addr32[3] == 0));
 
 		return false;
 	}
---8<---

---8<---

[root@localhost ~]# python3

quoted

quoted

from socket import *

s1 = socket(AF_INET6, SOCK_STREAM)
s1.bind(('::ffff:0.0.0.0', 0))
port = s1.getsockname()[1]

s2 = socket(AF_INET, SOCK_STREAM)
s2.bind(('127.0.0.1', port))

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 98] Address already in use
---8<---