linux-kernel - Re: [PATCH 2/2] mlxsw: spectrum_router: avoid potential uninitialized data usage

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Message-ID: <20160930175700.GA641@splinter>
Date:   Fri, 30 Sep 2016 20:57:00 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jiri Pirko <jiri@...lanox.com>, Ido Schimmel <idosch@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        Yotam Gigi <yotamg@...lanox.com>,
        Nogah Frankel <nogahf@...lanox.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mlxsw: spectrum_router: avoid potential
 uninitialized data usage

On Fri, Sep 30, 2016 at 06:17:10PM +0200, Arnd Bergmann wrote:
> If fi->fib_nhs is zero, the router interface pointer is uninitialized, as shown by
> this warning:
> 
> drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c: In function 'mlxsw_sp_router_fib_event':
> drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:1674:21: error: 'r' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:1643:23: note: 'r' was declared here
> 
> This changes the loop so we handle the case the same way as finding no router
> interface pointer attached to one of the nexthops to ensure we always
> trap here instead of using uninitialized data.
> 
> Fixes: b45f64d16d45 ("mlxsw: spectrum_router: Use FIB notifications instead of switchdev calls")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

For net-next:
Acked-by: Ido Schimmel <idosch@...lanox.com>

BTW, which flags did you pass to generate this error? I can only
reproduce this with EXTRA_CFLAGS="-Wmaybe-uninitialized -Werror", but
for some reason EXTRA_CFLAGS="-Wall -Werror" is silent. Any idea why? I
would like to add this to my git hooks and avoid these errors in the
future :)

Thanks!