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soreuseport: fix initialization race 

Syzkaller stumbled upon a way to trigger
WARNING: CPU: 1 PID: 13881 at net/core/sock_reuseport.c:41
reuseport_alloc+0x306/0x3b0 net/core/sock_reuseport.c:39

There are two initialization paths for the sock_reuseport structure in a
socket: Through the udp/tcp bind paths of SO_REUSEPORT sockets or through
SO_ATTACH_REUSEPORT_[CE]BPF before bind.  The existing implementation
assumedthat the socket lock protected both of these paths when it actually
only protects the SO_ATTACH_REUSEPORT path.  Syzkaller triggered this
double allocation by running these paths concurrently.

This patch moves the check for double allocation into the reuseport_alloc
function which is protected by a global spin lock.

Fixes: e32ea7e747 ("soreuseport: fast reuseport UDP socket selection")
Fixes: c125e80b88 ("soreuseport: fast reuseport TCP socket selection")
Signed-off-by: Craig Gallek <kraig@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Craig Gallek 2017-10-19 15:00:29 -04:00 committed by David S. Miller
parent 66c5451754
commit 1b5f962e71
3 changed files with 11 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
net/core/sock_reuseport.c
View File

@ -36,9 +36,14 @@ int reuseport_alloc(struct sock *sk)
* soft irq of receive path or setsockopt from process context
*/
spin_lock_bh(&reuseport_lock);
WARN_ONCE(rcu_dereference_protected(sk->sk_reuseport_cb,
lockdep_is_held(&reuseport_lock)),
"multiple allocations for the same socket");
/* Allocation attempts can occur concurrently via the setsockopt path
* and the bind/hash path. Nothing to do when we lose the race.
*/
if (rcu_dereference_protected(sk->sk_reuseport_cb,
lockdep_is_held(&reuseport_lock)))
goto out;
reuse = __reuseport_alloc(INIT_SOCKS);
if (!reuse) {
spin_unlock_bh(&reuseport_lock);
@ -49,6 +54,7 @@ int reuseport_alloc(struct sock *sk)
reuse->num_socks = 1;
rcu_assign_pointer(sk->sk_reuseport_cb, reuse);
out:
spin_unlock_bh(&reuseport_lock);
return 0;

5
net/ipv4/inet_hashtables.c
View File

@ -456,10 +456,7 @@ static int inet_reuseport_add_sock(struct sock *sk,
return reuseport_add_sock(sk, sk2);
}
/* Initial allocation may have already happened via setsockopt */
if (!rcu_access_pointer(sk->sk_reuseport_cb))
return reuseport_alloc(sk);
return 0;
return reuseport_alloc(sk);
}
int __inet_hash(struct sock *sk, struct sock *osk)

5
net/ipv4/udp.c
View File

@ -231,10 +231,7 @@ static int udp_reuseport_add_sock(struct sock *sk, struct udp_hslot *hslot)
}
}
/* Initial allocation may have already happened via setsockopt */
if (!rcu_access_pointer(sk->sk_reuseport_cb))
return reuseport_alloc(sk);
return 0;
return reuseport_alloc(sk);
}
/**