atm: clip: prevent NULL deref in clip_push()

Blamed commit missed that vcc_destroy_socket() calls
clip_push() with a NULL skb.

If clip_devs is NULL, clip_push() then crashes when reading
skb->truesize.

Fixes: 93a2014afbac ("atm: fix a UAF in lec_arp_clear_vccs()")
Reported-by: syzbot+1316233c4c6803382a8b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/68556f59.a00a0220.137b3.004e.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Gengming Liu <l.dmxcsnsbh@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/atm/clip.c b/net/atm/clip.c
index 61b5b700817de541d2882fb21f07992648460d4a..b234dc3bcb0d4aea0febff50d1b023cb7ad9dfe8 100644 (file)
--- a/net/atm/clip.c
+++ b/net/atm/clip.c
@@ -193,12 +193,6 @@ static void clip_push(struct atm_vcc *vcc, struct sk_buff *skb)
 
        pr_debug("\n");
 
-       if (!clip_devs) {
-               atm_return(vcc, skb->truesize);
-               kfree_skb(skb);
-               return;
-       }
-
        if (!skb) {
                pr_debug("removing VCC %p\n", clip_vcc);
                if (clip_vcc->entry)
@@ -208,6 +202,11 @@ static void clip_push(struct atm_vcc *vcc, struct sk_buff *skb)
                return;
        }
        atm_return(vcc, skb->truesize);
+       if (!clip_devs) {
+               kfree_skb(skb);
+               return;
+       }
+
        skb->dev = clip_vcc->entry ? clip_vcc->entry->neigh->dev : clip_devs;
        /* clip_vcc->entry == NULL if we don't have an IP address yet */
        if (!skb->dev) {