netdev - Re: [PATCH net] gre: fix uninit-value in __iptunnel_pull

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Message-Id: <20200308.212626.1535278286897905339.davem@davemloft.net>
Date:   Sun, 08 Mar 2020 21:26:26 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        syzkaller@...glegroups.com
Subject: Re: [PATCH net] gre: fix uninit-value in __iptunnel_pull_header

From: Eric Dumazet <edumazet@...gle.com>
Date: Sat,  7 Mar 2020 22:05:14 -0800

> syzbot found an interesting case of the kernel reading
> an uninit-value [1]
> 
> Problem is in the handling of ETH_P_WCCP in gre_parse_header()
> 
> We look at the byte following GRE options to eventually decide
> if the options are four bytes longer.
> 
> Use skb_header_pointer() to not pull bytes if we found
> that no more bytes were needed.
> 
> All callers of gre_parse_header() are properly using pskb_may_pull()
> anyway before proceeding to next header.
> 
> [1]
 ...
> Fixes: 95f5c64c3c13 ("gre: Move utility functions to common headers")
> Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied and queued up for -stable, thanks.