From b2be05c99e28875604ef336437840554a077f7ee Mon Sep 17 00:00:00 2001
From: Tom Herbert <tom@quantonium.net>
Date: Wed, 24 Jan 2018 12:35:41 -0800
Subject: [PATCH 4/4] kcm: Check if sk_user_data already set in kcm_attach
Git-commit: e5571240236c5652f3e079b1d5866716a7ad819c
Patch-mainline: v4.15
References: git-fixes
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>
Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
---
net/kcm/kcmsock.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index be4678994e86..99072284cd8c 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1410,9 +1410,18 @@ static int kcm_attach(struct socket *soc
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;
@@ -1429,8 +1438,11 @@ 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;
--
2.16.4