Commit 1f770c0a authored by Herbert Xu's avatar Herbert Xu Committed by David S. Miller
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netlink: Fix autobind race condition that leads to zero port ID 



The commit c0bb07df ("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: c0bb07df ("netlink: Reset portid after netlink_insert failure")
Reported-by: default avatarTejun Heo <tj@kernel.org>
Reported-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 3ea79249

net/netlink/af_netlink.c

+7 −5
Original line number Diff line number Diff line
@@ -1031,7 +1031,7 @@ static inline int netlink_compare(struct rhashtable_compare_arg *arg, 
	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 @@ static int __netlink_insert(struct netlink_table *table, struct sock *sk) 
{

	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 @@ static int netlink_insert(struct sock *sk, u32 portid) 
	    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 @@ static int netlink_insert(struct sock *sk, u32 portid) 
			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 @@ static inline u32 netlink_hash(const void *data, u32 len, u32 seed) 
	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);

}

net/netlink/af_netlink.h

+1 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ struct netlink_ring { 
struct netlink_sock {

	/* struct sock has to be the first member of netlink_sock */

	struct sock		sk;

	u32			rhash_portid;

	u32			portid;

	u32			dst_portid;

	u32			dst_group;

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