On 2018年05月16日 15:12, Andrei Vagin wrote:
Hi Jason,

I think the problem is in "tun: hold a tun socket during ptr_ring_cleanup".

Pls take a look at the attached patch.


It looks to me it's not necessary to take extra refcnt during release, we can just do the cleanup at __tun_detach().

Could you help to test the attached patch?


>From 4b5ad75208e379dcb32abb9ac4790a0446f8558b Mon Sep 17 00:00:00 2001
From: Jason Wang <jasow...@redhat.com>
Date: Wed, 16 May 2018 15:26:52 +0800
Subject: [PATCH] tuntap: fix use after free during release

After commit b196d88aba8a ("tun: fix use after free for ptr_ring") we
need clean up tx ring during release(). But unfortunately, it tries to
do the cleanup after socket were destroyed which will lead another
use-after-free. Fix this by doing the cleanup before dropping the last
reference of the socket in __tun_detach().

Reported-by: Andrei Vagin <ava...@virtuozzo.com>
Fixes: b196d88aba8a ("tun: fix use after free for ptr_ring")
Signed-off-by: Jason Wang <jasow...@redhat.com>
 drivers/net/tun.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 9fbbb32..d45ac37 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -729,6 +729,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
 		if (tun)
+		ptr_ring_cleanup(&tfile->tx_ring, tun_ptr_free);
@@ -3245,7 +3246,6 @@ static int tun_chr_close(struct inode *inode, struct file *file)
 	struct tun_file *tfile = file->private_data;
 	tun_detach(tfile, true);
-	ptr_ring_cleanup(&tfile->tx_ring, tun_ptr_free);
 	return 0;

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