netfilter: drop outermost socket lock in getsockopt()

The Syzbot reported a possible deadlock in the netfilter area caused by
rtnl lock, xt lock and socket lock being acquired with a different order
on different code paths, leading to the following backtrace:
Reviewed-by: Xin Long <lucien.xin@gmail.com>

======================================================
WARNING: possible circular locking dependency detected
4.15.0+ #301 Not tainted
------------------------------------------------------
syzkaller233489/4179 is trying to acquire lock:
  (rtnl_mutex){+.+.}, at: [<0000000048e996fd>] rtnl_lock+0x17/0x20
net/core/rtnetlink.c:74

but task is already holding lock:
  (&xt[i].mutex){+.+.}, at: [<00000000328553a2>]
xt_find_table_lock+0x3e/0x3e0 net/netfilter/x_tables.c:1041

which lock already depends on the new lock.
===

Since commit 3f34cfae1230 ("netfilter: on sockopt() acquire sock lock
only in the required scope"), we already acquire the socket lock in
the innermost scope, where needed. In such commit I forgot to remove
the outer-most socket lock from the getsockopt() path, this commit
addresses the issues dropping it now.

v1 -> v2: fix bad subj, added relavant 'fixes' tag

Fixes: 22265a5c3c10 ("netfilter: xt_TEE: resolve oif using netdevice notifiers")
Fixes: 202f59afd441 ("netfilter: ipt_CLUSTERIP: do not hold dev")
Fixes: 3f34cfae1230 ("netfilter: on sockopt() acquire sock lock only in the required scope")
Reported-by: syzbot+ddde1c7b7ff7442d7f2d@syzkaller.appspotmail.com
Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 2 insertions, 8 deletions

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index d78d41fc4b1a..24535169663d 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -1367,10 +1367,7 @@ int ipv6_getsockopt(struct sock *sk, int level, int optname,
 		if (get_user(len, optlen))
 			return -EFAULT;
 
-		lock_sock(sk);
-		err = nf_getsockopt(sk, PF_INET6, optname, optval,
-				&len);
-		release_sock(sk);
+		err = nf_getsockopt(sk, PF_INET6, optname, optval, &len);
 		if (err >= 0)
 			err = put_user(len, optlen);
 	}
@@ -1409,10 +1406,7 @@ int compat_ipv6_getsockopt(struct sock *sk, int level, int optname,
 		if (get_user(len, optlen))
 			return -EFAULT;
 
-		lock_sock(sk);
-		err = compat_nf_getsockopt(sk, PF_INET6,
-					   optname, optval, &len);
-		release_sock(sk);
+		err = compat_nf_getsockopt(sk, PF_INET6, optname, optval, &len);
 		if (err >= 0)
 			err = put_user(len, optlen);
 	}