netdev - Re: UBSAN: object-size-mismatch in wg

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Message-ID: <68452c93-de95-aaa6-3cac-d868a202ea6f@linux.ibm.com>
Date:   Thu, 7 Jan 2021 18:01:19 +0100
From:   Julian Wiedmann <jwi@...ux.ibm.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Kees Cook <keescook@...gle.com>, Netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: UBSAN: object-size-mismatch in wg_xmit

On 21.12.20 12:23, Jason A. Donenfeld wrote:
> Hi Dmitry,
> 

...

> fall on the border of a mapping? Is UBSAN non-deterministic as an
> optimization? Or is there actually some mysterious UaF happening with
> my usage of skbs that I shouldn't overlook?
> 

One oddity is that wg_xmit() returns negative errnos, rather than a
netdev_tx_t (ie. NETDEV_TX_OK or NETDEV_TX_BUSY).

Any chance that the stack mis-interprets one of those custom errnos
as NETDEV_TX_BUSY, and thus believes that it still owns the skb?

> Jason
>