[SRU][B/linux][PATCH] tap: fix use-after-free

Juerg Haefliger juerg.haefliger at canonical.com
Fri Jul 31 08:28:33 UTC 2020

From: "Michael S. Tsirkin" <mst at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1889735

Lockless access to __ptr_ring_full is only legal if ring is
never resized, otherwise it might cause use-after free errors.
Simply drop the lockless test, we'll drop the packet
a bit later when produce fails.

Fixes: 362899b8 ("macvtap: switch to use skb array")
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Signed-off-by: David S. Miller <davem at davemloft.net>

(backported from commit 88fae87327a2261cf8db078f6ce4e5a3e55b30b1)
[juergh: __ptr_ring_full() -> __skb_array_full() due to lack of commit
 5990a30510ed ("tun/tap: use ptr_ring instead of skb_array").]
Signed-off-by: Juerg Haefliger <juergh at canonical.com>
 drivers/net/tap.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index afbe5bec2c33..f8b44d395c2f 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -330,9 +330,6 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
 	if (!q)
 		return RX_HANDLER_PASS;
-	if (__skb_array_full(&q->skb_array))
-		goto drop;
 	skb_push(skb, ETH_HLEN);
 	/* Apply the forward feature mask so that we perform segmentation

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