netdev - Re: [PATCH net] ipv4: ip_gre: Handle skb_pull() failure in ipgre

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Date: Tue, 28 Nov 2023 16:51:09 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>, Shigeru Yoshida <syoshida@...hat.com>
Cc: davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] ipv4: ip_gre: Handle skb_pull() failure in
 ipgre_xmit()

On Tue, 2023-11-28 at 16:45 +0100, Eric Dumazet wrote:
> On Sun, Nov 26, 2023 at 4:17 PM Shigeru Yoshida <syoshida@...hat.com> wrote:
> > 
> > In ipgre_xmit(), skb_pull() may fail even if pskb_inet_may_pull() returns
> > true. For example, applications can create a malformed packet that causes
> > this problem with PF_PACKET.
> > 
> > This patch fixes the problem by dropping skb and returning from the
> > function if skb_pull() fails.
> > 
> > Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
> > Signed-off-by: Shigeru Yoshida <syoshida@...hat.com>
> > ---
> >  net/ipv4/ip_gre.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
> > index 22a26d1d29a0..95efa97cb84b 100644
> > --- a/net/ipv4/ip_gre.c
> > +++ b/net/ipv4/ip_gre.c
> > @@ -643,7 +643,8 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
> >                 /* Pull skb since ip_tunnel_xmit() needs skb->data pointing
> >                  * to gre header.
> >                  */
> > -               skb_pull(skb, tunnel->hlen + sizeof(struct iphdr));
> > +               if (!skb_pull(skb, tunnel->hlen + sizeof(struct iphdr)))
> > +                       goto free_skb;
> >                 skb_reset_mac_header(skb);
> > 
> >                 if (skb->ip_summed == CHECKSUM_PARTIAL &&
> > --
> 
> 
> I have syszbot reports with an actual repro for this one.

Could you please share them? I could not find easily the reports in
https://syzkaller.appspot.com/upstream

Thanks,

Paolo