[PATCH v2 1/5] nvme: reject a reconnect_delay of 0 through sysfs

[Guixin Liu <kanie@linux.alibaba.com>]

nvme_ctrl_reconnect_delay_store() accepts any value the option parser
also accepts, except that it misses the lower bound: writing 0 is
rejected by nvmf_parse_options() but not by the sysfs attribute.
nvme_ctrl_loss_tmo_store() then divides by opts->reconnect_delay in
DIV_ROUND_UP(), so writing 0 followed by any ctrl_loss_tmo update
crashes the kernel with a division by zero.

Reject 0 like the option parser does.

Fixes: 764075fdcb2f ("nvme: expose reconnect_delay and ctrl_loss_tmo via sysfs")
Cc: stable@vger.kernel.org
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
---

Reproduced on an unfixed 7.3.0-rc7 kernel in a VM with a fabrics
controller connected:

  echo 0 > /sys/class/nvme/nvme1/reconnect_delay
  echo 30 > /sys/class/nvme/nvme1/ctrl_loss_tmo

  Oops: divide error: 0000 [#1] SMP KASAN PTI
  CPU: 7 UID: 0 PID: 1542 Comm: bash Not tainted 7.3.0-rc7
  RIP: 0010:nvme_ctrl_loss_tmo_store+0xce/0x120 [nvme_core]
  Code: ... 8d 44 08 ff <f7> f1 ...
  RAX: 000000000000001d RCX: 0000000000000000

Verified on the patched kernel: writing 0 returns -EINVAL and the
ctrl_loss_tmo update succeeds without an oops.
---
 drivers/nvme/host/sysfs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/nvme/host/sysfs.c b/drivers/nvme/host/sysfs.c
index 10018c6356b6..bae0d6258d01 100644
--- a/drivers/nvme/host/sysfs.c
+++ b/drivers/nvme/host/sysfs.c
@@ -634,6 +634,9 @@ static ssize_t nvme_ctrl_reconnect_delay_store(struct device *dev,
 	if (err)
 		return err;
 
+	if (!v)
+		return -EINVAL;
+
 	ctrl->opts->reconnect_delay = v;
 	return count;
 }
-- 
2.43.7