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

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Message-ID: <20231204140743.1487843-1-stefanha@redhat.com>
Date:   Mon,  4 Dec 2023 09:07:43 -0500
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        virtualization@...ts.linux.dev, Jason Wang <jasowang@...hat.com>,
        linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        linux-block@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Suwan Kim <suwan.kim027@...il.com>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH] virtio_blk: fix snprintf truncation compiler warning

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>
---
 drivers/block/virtio_blk.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index d53d6aa8ee69..47556d8ccc32 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -1019,12 +1019,12 @@ static void virtblk_config_changed(struct virtio_device *vdev)
 static int init_vq(struct virtio_blk *vblk)
 {
 	int err;
-	int i;
+	unsigned short i;
 	vq_callback_t **callbacks;
 	const char **names;
 	struct virtqueue **vqs;
 	unsigned short num_vqs;
-	unsigned int num_poll_vqs;
+	unsigned short num_poll_vqs;
 	struct virtio_device *vdev = vblk->vdev;
 	struct irq_affinity desc = { 0, };
 
@@ -1068,13 +1068,13 @@ static int init_vq(struct virtio_blk *vblk)
 
 	for (i = 0; i < num_vqs - num_poll_vqs; i++) {
 		callbacks[i] = virtblk_done;
-		snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
+		snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%u", i);
 		names[i] = vblk->vqs[i].name;
 	}
 
 	for (; i < num_vqs; i++) {
 		callbacks[i] = NULL;
-		snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
+		snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%u", i);
 		names[i] = vblk->vqs[i].name;
 	}
 
-- 
2.43.0