lkml.org 
[lkml]   [2015]   [Nov]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRE: [Resend PATCH] RDS: fix race condition when sending a message on unbound socket
Date
From: Santosh Shilimkar
> Sent: 24 November 2015 22:13
...
> Sasha's found a NULL pointer dereference in the RDS connection code when
> sending a message to an apparently unbound socket. The problem is caused
> by the code checking if the socket is bound in rds_sendmsg(), which checks
> the rs_bound_addr field without taking a lock on the socket. This opens a
> race where rs_bound_addr is temporarily set but where the transport is not
> in rds_bind(), leading to a NULL pointer dereference when trying to
> dereference 'trans' in __rds_conn_create().
>
> Vegard wrote a reproducer for this issue, so kindly ask him to share if
> you're interested.
...
> diff --git a/net/rds/send.c b/net/rds/send.c
> index 827155c..c9cdb35 100644
> --- a/net/rds/send.c
> +++ b/net/rds/send.c
> @@ -1013,11 +1013,13 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
> release_sock(sk);

This is falling though into an unconditional lock_sock().
No need to unlock and relock immediately.

> }
>
> - /* racing with another thread binding seems ok here */
> + lock_sock(sk);
> if (daddr == 0 || rs->rs_bound_addr == 0) {
> + release_sock(sk);
> ret = -ENOTCONN; /* XXX not a great errno */
> goto out;
> }
> + release_sock(sk);
>

On the face of it the above looks somewhat dubious.
Locks usually tie together two action (eg a test and use of a value),
In this case you only have a test inside the lock.
That either means that the state can change after you release the lock
(ie rs->rs_bound_addr = 0 is executed somewhere), or you don't
really need the lock.

David




\
 
 \ /
  Last update: 2015-11-25 13:41    [W:0.046 / U:0.444 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site