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kcm: Check if sk_user_data already set in kcm_attach 

This is needed to prevent sk_user_data being overwritten.
The check is done under the callback lock. This should prevent
a socket from being attached twice to a KCM mux. It also prevents
a socket from being attached for other use cases of sk_user_data
as long as the other cases set sk_user_data under the lock.
Followup work is needed to unify all the use cases of sk_user_data
to use the same locking.

Reported-by: syzbot+114b15f2be420a8886c3@syzkaller.appspotmail.com
Fixes: ab7ac4eb98 ("kcm: Kernel Connection Multiplexor module")
Signed-off-by: Tom Herbert <tom@quantonium.net>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Tom Herbert 2018-01-24 12:35:41 -08:00 committed by David S. Miller
parent 581e7226a5
commit e557124023
1 changed files with 14 additions and 2 deletions
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16
net/kcm/kcmsock.c
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@ -1410,9 +1410,18 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
return err;
}
sock_hold(csk);
write_lock_bh(&csk->sk_callback_lock);
/* Check if sk_user_data is aready by KCM or someone else.
* Must be done under lock to prevent race conditions.
*/
if (csk->sk_user_data) {
write_unlock_bh(&csk->sk_callback_lock);
strp_done(&psock->strp);
kmem_cache_free(kcm_psockp, psock);
return -EALREADY;
}
psock->save_data_ready = csk->sk_data_ready;
psock->save_write_space = csk->sk_write_space;
psock->save_state_change = csk->sk_state_change;
@ -1420,8 +1429,11 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
csk->sk_data_ready = psock_data_ready;
csk->sk_write_space = psock_write_space;
csk->sk_state_change = psock_state_change;
write_unlock_bh(&csk->sk_callback_lock);
sock_hold(csk);
/* Finished initialization, now add the psock to the MUX. */
spin_lock_bh(&mux->lock);
head = &mux->psocks;