linux-kernel - Re: [PATCH] virtio_blk: fix snprintf truncation compiler warning

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Message-ID: <3b2bfd2f-5306-4a70-b1d9-6c41e72cd939@nvidia.com>
Date:   Tue, 5 Dec 2023 06:59:17 +0000
From:   Chaitanya Kulkarni <chaitanyak@...dia.com>
To:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
CC:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        "virtualization@...ts.linux.dev" <virtualization@...ts.linux.dev>,
        Jason Wang <jasowang@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Suwan Kim <suwan.kim027@...il.com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] virtio_blk: fix snprintf truncation compiler warning

On 12/4/2023 6:07 AM, Stefan Hajnoczi wrote:
> Commit 4e0400525691 ("virtio-blk: support polling I/O") triggers the
> following gcc 13 W=1 warnings:
> 
> drivers/block/virtio_blk.c: In function ‘init_vq’:
> drivers/block/virtio_blk.c:1077:68: warning: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 7 [-Wformat-truncation=]
>   1077 |                 snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
>        |                                                                    ^~
> drivers/block/virtio_blk.c:1077:58: note: directive argument in the range [-2147483648, 65534]
>   1077 |                 snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
>        |                                                          ^~~~~~~~~~~~~
> drivers/block/virtio_blk.c:1077:17: note: ‘snprintf’ output between 11 and 21 bytes into a destination of size 16
>   1077 |                 snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
>        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> This is a false positive because the lower bound -2147483648 is
> incorrect. The true range of i is [0, num_vqs - 1] where 0 < num_vqs <
> 65536.
> 
> The code mixes int, unsigned short, and unsigned int types in addition
> to using "%d" for an unsigned value. Use unsigned short and "%u"
> consistently to solve the compiler warning.
> 
> Cc: Suwan Kim <suwan.kim027@...il.com>
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202312041509.DIyvEt9h-lkp@intel.com/
> Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
> ---

Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>

-ck