netlink: Fix autobind race condition that leads to zero port ID
The commit c0bb07df7d981e4091432754e30c9c720e2c0c78 ("netlink:
Reset portid after netlink_insert failure") introduced a race
condition where if two threads try to autobind the same socket
one of them may end up with a zero port ID. This led to kernel
deadlocks that were observed by multiple people.
This patch reverts that commit and instead fixes it by introducing
a separte rhash_portid variable so that the real portid is only set
after the socket has been successfully hashed.
Fixes: c0bb07df7d98 ("netlink: Reset portid after netlink_insert failure")
Reported-by: Tejun Heo <tj@kernel.org>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 4cad99d..9f51608 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1031,7 +1031,7 @@
const struct netlink_compare_arg *x = arg->key;
const struct netlink_sock *nlk = ptr;
- return nlk->portid != x->portid ||
+ return nlk->rhash_portid != x->portid ||
!net_eq(sock_net(&nlk->sk), read_pnet(&x->pnet));
}
@@ -1057,7 +1057,7 @@
{
struct netlink_compare_arg arg;
- netlink_compare_arg_init(&arg, sock_net(sk), nlk_sk(sk)->portid);
+ netlink_compare_arg_init(&arg, sock_net(sk), nlk_sk(sk)->rhash_portid);
return rhashtable_lookup_insert_key(&table->hash, &arg,
&nlk_sk(sk)->node,
netlink_rhashtable_params);
@@ -1119,7 +1119,7 @@
unlikely(atomic_read(&table->hash.nelems) >= UINT_MAX))
goto err;
- nlk_sk(sk)->portid = portid;
+ nlk_sk(sk)->rhash_portid = portid;
sock_hold(sk);
err = __netlink_insert(table, sk);
@@ -1131,10 +1131,12 @@
err = -EOVERFLOW;
if (err == -EEXIST)
err = -EADDRINUSE;
- nlk_sk(sk)->portid = 0;
sock_put(sk);
+ goto err;
}
+ nlk_sk(sk)->portid = portid;
+
err:
release_sock(sk);
return err;
@@ -3271,7 +3273,7 @@
const struct netlink_sock *nlk = data;
struct netlink_compare_arg arg;
- netlink_compare_arg_init(&arg, sock_net(&nlk->sk), nlk->portid);
+ netlink_compare_arg_init(&arg, sock_net(&nlk->sk), nlk->rhash_portid);
return jhash2((u32 *)&arg, netlink_compare_arg_len / sizeof(u32), seed);
}