Re: [PATCH 1/2] nvme: Update type from size_t to u16 for opts->queue_size

[Nitesh Shetty]

On 29/11/23 12:26PM, Dan Carpenter wrote:
> On Tue, Nov 28, 2023 at 05:59:56PM +0530, Nitesh Shetty wrote:
> > This fixes the smatch warning, "nvme_loop_create_ctrl() warn:
> > 'opts->queue_size - 1' 18446744073709551615 can't fit into 65535
> > 'ctrl->ctrl.sqsize'"
> > We don't need size_t for queue_size, u16 should serve the purpose,
> > as max size is limited to NVMF_DEF_QUEUE_SIZE(1024).
> >
> > Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
>
> Huh...  I'm sorry I wasn't necessarily aware that I had published this
> Smatch warning.  I feel like it has a high rate of false positives.
>
> Generally with Smatch warnings, I'm not going to try silence every
> false positive.  And I had one complaint recently that I was too focused
> on silencing false positives instead of discovering new bugs...
>
> The other thing about static analysis is that static checker developers
> want 0% false positives and kernel developers want 100% false positives.
> I'm a kernel developer so in code that I have looked at the rate of
> false positives is very close to 100%.  Only new code has valid
> warnings.
>
> Here is what this code looks like:
>
> drivers/nvme/target/loop.c
>   573          if (opts->queue_size > ctrl->ctrl.maxcmd) {
>   574                  /* warn if maxcmd is lower than queue_size */
>   575                  dev_warn(ctrl->ctrl.device,
>   576                          "queue_size %zu > ctrl maxcmd %u, clamping down\n",
>   577                          opts->queue_size, ctrl->ctrl.maxcmd);
>   578                  opts->queue_size = ctrl->ctrl.maxcmd;
>   579          }
>   580          ctrl->ctrl.sqsize = opts->queue_size - 1;
>
> Smatch thinks that opts->queue_size is a value that comes from the user
> in the 16-47 range.  But the bug is that Smatch thinks that
> ctrl->ctrl.maxcmd is zero.  16 is greater than zero so we do the
> opts->queue_size = ctrl->ctrl.maxcmd; assignment.  Then zero minus one
> is ULONG_MAX so that's a very high number.
>
> Smatch is just wrong in this case.  Let me try figure out what went
> wrong.  The ctrl->ctrl.maxcmd = 0 comes from:
>
> 	ctrl = kzalloc(sizeof(*ctrl), GFP_KERNEL);
>
> It's supposed to get set to unknown in nvme_loop_configure_admin_queue().
> The database has the correct data.
>
> $ smdb.py return_states nvme_loop_configure_admin_queue | grep maxcmd
> drivers/nvme/target/loop.c | nvme_loop_configure_admin_queue | 229 |             0|       PARAM_SET |  0 |       $->ctrl.maxcmd |             0-u16max |
> drivers/nvme/target/loop.c | nvme_loop_configure_admin_queue | 231 | s32min-(-1),1-s32max|       PARAM_ADD |  0 |       $->ctrl.maxcmd |             0-u16max |
>
> But the issue is that Smatch thinks that nvme_loop_configure_admin_queue()
> always fails with -12.  The reason for that is because Smatch thinks
> that ctrl->ctrl.ops is NULL but the function can only succeed when it's
> non-NULL.
>
> The ctrl->ops assignment happens in nvme_init_ctrl() and it should have
> been easy to track.  I am not sure what went wrong there.  I'll take a
> look at that and fix it.

Thank you for this insight.
I ran smatch on complete kernel using smatch's test_kernel.sh
I was unaware of this smbd.py option. I will explore this.
Meanwhile I feel this patch is still relevant, as it aligns opts
queue_size with size of ctrl queue_size.

Regards,
Nitesh Shetty