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

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Date:   Mon, 11 Jan 2021 18:58:34 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     noloader@...il.com
Cc:     Netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>
Subject: Re: UBSAN: object-size-mismatch in wg_xmit

On Mon, Jan 11, 2021 at 6:35 PM Jeffrey Walton <noloader@...il.com> wrote:
>
> On Mon, Jan 11, 2021 at 12:20 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > ...
> > FTR, I've disabled the following UBSAN configs:
> > UBSAN_MISC
> > UBSAN_DIV_ZERO
> > UBSAN_BOOL
> > UBSAN_OBJECT_SIZE
> > UBSAN_SIGNED_OVERFLOW
> > UBSAN_UNSIGNED_OVERFLOW
> > UBSAN_ENUM
> > UBSAN_ALIGNMENT
> > UBSAN_UNREACHABLE
> >
> > Only these are enabled now:
> > UBSAN_BOUNDS
> > UBSAN_SHIFT
> >
> > This is commit:
> > https://github.com/google/syzkaller/commit/2c1f2513486f21d26b1942ce77ffc782677fbf4e
>
> I think the commit cut too deep.
>
> The overflows are important if folks are building with compilers other than GCC.
>
> The aligned data accesses are important on platforms like MIPS64 and Sparc64.
>
> Object size is important because it catches destination buffer overflows.
>
> I don't know what's in miscellaneous. There may be something useful in there.

Hi Jeff,

See the commit for reasons why each of these is disabled.
E.g. object size, somebody first needs to fix bugs like this one.
While things like skbuff have these UBs on trivial workloads, there is
no point in involving fuzzing and making it crash on this trivial bug
all the time and stopping doing any other kernel testing as the
result.