2021-04-13 10:15:03

by Or Cohen

Subject: [PATCH] net/sctp: fix race condition in sctp_destroy_sock

If sctp_destroy_sock is called without sock_net(sk)->sctp.addr_wq_lock
held and sp->do_auto_asconf is true, then an element is removed
from the auto_asconf_splist without any proper locking.

This can happen in the following functions:
1. In sctp_accept, if sctp_sock_migrate fails.
2. In inet_create or inet6_create, if there is a bpf program
attached to BPF_CGROUP_INET_SOCK_CREATE which denies
creation of the sctp socket.

The bug is fixed by acquiring addr_wq_lock in sctp_destroy_sock
instead of sctp_close.

Reported-by: Or Cohen <[email protected]>
Reviewed-by: Xin Long <[email protected]>
Fixes: 610236587600 ("bpf: Add new cgroup attach type to enable sock modifications")
Signed-off-by: Or Cohen <[email protected]>
---
net/sctp/socket.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index a710917c5ac7..9af232d4fb6b 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1520,11 +1520,9 @@ static void sctp_close(struct sock *sk, long timeout)

/* Supposedly, no process has access to the socket, but
* the net layers still may.
- * Also, sctp_destroy_sock() needs to be called with addr_wq_lock
- * held and that should be grabbed before socket lock.
*/
- spin_lock_bh(&net->sctp.addr_wq_lock);
- bh_lock_sock_nested(sk);
+ local_bh_disable();
+ bh_lock_sock(sk);

/* Hold the sock, since sk_common_release() will put sock_put()
* and we have just a little more cleanup.
@@ -1533,7 +1531,7 @@ static void sctp_close(struct sock *sk, long timeout)
sk_common_release(sk);

bh_unlock_sock(sk);
- spin_unlock_bh(&net->sctp.addr_wq_lock);
+ local_bh_enable();

sock_put(sk);

@@ -5030,7 +5028,9 @@ static void sctp_destroy_sock(struct sock *sk)

if (sp->do_auto_asconf) {
sp->do_auto_asconf = 0;
+ spin_lock_bh(&sock_net(sk)->sctp.addr_wq_lock);
list_del(&sp->auto_asconf_list);
+ spin_unlock_bh(&sock_net(sk)->sctp.addr_wq_lock);
}
sctp_endpoint_free(sp->ep);
local_bh_disable();
--
2.7.4

2021-04-13 21:00:44

by Marcelo Ricardo Leitner

Subject: Re: [PATCH] net/sctp: fix race condition in sctp_destroy_sock

On Tue, Apr 13, 2021 at 12:31:53PM +0300, Or Cohen wrote:
> +++ b/net/sctp/socket.c
> @@ -1520,11 +1520,9 @@ static void sctp_close(struct sock *sk, long timeout)
>
> /* Supposedly, no process has access to the socket, but
> * the net layers still may.
> - * Also, sctp_destroy_sock() needs to be called with addr_wq_lock
> - * held and that should be grabbed before socket lock.
> */

Please also update the following comment in sctp_init_sock():
/* Nothing can fail after this block, otherwise
* sctp_destroy_sock() will be called without addr_wq_lock held
*/

Other than this, LGTM. Thanks.

Marcelo