netdev - Re: tun issue after e0b46d0ee9c: tun: Use iovec iterators

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Message-ID: <20141130100331.GA10050@gondor.apana.org.au>
Date:	Sun, 30 Nov 2014 18:03:31 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Marcelo Ricardo Leitner <mleitner@...hat.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: tun issue after e0b46d0ee9c: tun: Use iovec iterators

On Sat, Nov 29, 2014 at 07:59:35AM +0800, Herbert Xu wrote:
> On Fri, Nov 28, 2014 at 05:25:27PM -0200, Marcelo Ricardo Leitner wrote:
> > 
> > I saw there are tun updates on Dave's queue but none seemed to handle this.
> > 
> > I can't use current net-next
> > (799d2fff1858004526ad75d66a5dd8a5cce6ad40) on a kvm hypervisor
> > because tun got clogged somehow. Bisected down to:
> > 
> > commit e0b46d0ee9c240c7430a47e9b0365674d4a04522
> > Author: Herbert Xu <herbert@...dor.apana.org.au>
> > Date:   Fri Nov 7 21:22:23 2014 +0800
> 
> Does this patch help?

Oops, there was an embarrassing typo in the patch which causes
it to not even build.  Here is the corrected version.

-- >8 --
Subject: tun: Fix GSO meta-data handling in tun_get_user
    
When we write the GSO meta-data in tun_get_user we end up advancing
the IO vector twice, thus exhausting the user buffer before we can
finish writing the packet.
    
Fixes: f5ff53b4d97c ("{macvtap,tun}_get_user(): switch to iov_iter")
Reported-by: Marcelo Ricardo Leitner <mleitner@...hat.com>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 4b743c6..6d44da1 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1052,7 +1052,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 
 		if (gso.hdr_len > len)
 			return -EINVAL;
-		iov_iter_advance(from, tun->vnet_hdr_sz);
+		iov_iter_advance(from, tun->vnet_hdr_sz - sizeof(gso));
 	}
 
 	if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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