path: root/net/kcm
diff options
authorTom Herbert <tom@quantonium.net>2018-01-24 12:35:41 -0800
committerDavid S. Miller <davem@davemloft.net>2018-01-24 15:54:30 -0500
commite5571240236c5652f3e079b1d5866716a7ad819c (patch)
tree1541ccbaf77a4b034f515865927e175bb7e00bc0 /net/kcm
parentkcm: Only allow TCP sockets to be attached to a KCM mux (diff)
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: ab7ac4eb9832 ("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>
Diffstat (limited to 'net/kcm')
1 files changed, 14 insertions, 2 deletions
diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 7632797fb68e..4a8d407f8902 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1410,9 +1410,18 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
return err;
- sock_hold(csk);
+ /* 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;
+ sock_hold(csk);
/* Finished initialization, now add the psock to the MUX. */
head = &mux->psocks;