linux-kernel - Re: [PATCH net] net: fix skb leak in __skb_tstamp

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Message-ID: <20230522170430.56198-1-kuniyu@amazon.com>
Date:   Mon, 22 May 2023 10:04:30 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     <sj@...nel.org>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <kuniyu@...zon.com>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>, <nmanthey@...zon.de>,
        <pabeni@...hat.com>, <ptyadav@...zon.de>, <willemb@...gle.com>
Subject: Re: [PATCH net] net: fix skb leak in __skb_tstamp_tx()

From: SeongJae Park <sj@...nel.org>
Date: Mon, 22 May 2023 16:55:05 +0000
> Hi Pratyush,
> 
> On Mon, 22 May 2023 17:30:20 +0200 Pratyush Yadav <ptyadav@...zon.de> wrote:
> 
> > Commit 50749f2dd685 ("tcp/udp: Fix memleaks of sk and zerocopy skbs with
> > TX timestamp.") added a call to skb_orphan_frags_rx() to fix leaks with
> > zerocopy skbs. But it ended up adding a leak of its own. When
> > skb_orphan_frags_rx() fails, the function just returns, leaking the skb
> > it just cloned. Free it before returning.
> > 
> > This bug was discovered and resolved using Coverity Static Analysis
> > Security Testing (SAST) by Synopsys, Inc.
> > 
> > Fixes: 50749f2dd685 ("tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp.")
> 
> Seems the commit has merged in several stable kernels.  Is the bug also
> affecting those?  If so, would it be better to Cc stable@...r.kernel.org?

In netdev, we add 'net' in Subject for bugfix, then netdev maintainers
send a pull request weekly, and stable maintainers backport the fixes to
affected trees.

So we usually need not CC stable for netdev patches.

Thanks,
Kuniyuki

> 
> 
> Thanks,
> SJ
> 
> > Signed-off-by: Pratyush Yadav <ptyadav@...zon.de>
> > ---
> > 
> > I do not know this code very well, this was caught by our static
> > analysis tool. I did not try specifically reproducing the leak but I did
> > do a boot test by adding this patch on 6.4-rc3 and the kernel boots
> > fine.
> > 
> >  net/core/skbuff.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 515ec5cdc79c..cea28d30abb5 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -5224,8 +5224,10 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
> >  	} else {
> >  		skb = skb_clone(orig_skb, GFP_ATOMIC);
> > 
> > -		if (skb_orphan_frags_rx(skb, GFP_ATOMIC))
> > +		if (skb_orphan_frags_rx(skb, GFP_ATOMIC)) {
> > +			kfree_skb(skb);
> >  			return;
> > +		}
> >  	}
> >  	if (!skb)
> >  		return;
> > --
> > 2.39.2
> >