From: Klaus Jensen <k.jensen@samsung.com>

In nvme_format_ns(), if the namespace is of zero size (which might be
useless, but not invalid), the `count` variable will leak. Fix this by
returning early in that case.

Reported-by: Coverity (CID 1451082)
Fixes: dc04d25e2f3f ("hw/block/nvme: add support for the format nvm command")
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
---
 hw/block/nvme.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index 6842b01ab58b..dad275971a84 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -4984,6 +4984,11 @@ static uint16_t nvme_format_ns(NvmeCtrl *n, NvmeNamespace *ns, uint8_t lbaf,
     ns->status = NVME_FORMAT_IN_PROGRESS;
 
     len = ns->size;
+
+    if (!len) {
+        return NVME_SUCCESS;
+    }
+
     offset = 0;
 
     count = g_new(int, 1);
-- 
2.31.0

On 22.03.21 07:19, Klaus Jensen wrote:
> From: Klaus Jensen <k.jensen@samsung.com>
> 
> In nvme_format_ns(), if the namespace is of zero size (which might be
> useless, but not invalid), the `count` variable will leak. Fix this by
> returning early in that case.

When looking at the Coverity report, something else caught my eye: As 
far as I’m aware, blk_aio_pwrite_zeroes() may invoke the CB before 
returning (if blk_do_pwritev_part() returns without yielding).  I don’t 
think that will happen with real hardware (who knows, though), but it 
should be possible to see with the null-co block driver.

nvme_format_ns() doesn’t quite look like it takes that into account. 
For example, because *count starts at 1 and is decremented after the 
while (len) loop, all nvme_aio_format_cb() invocations (if they are 
invoked before their blk_aio_pwrite_zeroes() returns) will see
*count == 2, and thus not free it, or call nvme_enqueue_req_completion().

I don’t know whether the latter is problematic, but not freeing `count` 
doesn’t seem right.  Perhaps this could be addressed by adding a 
condition to the `(*count)--` to see whether `(*count)-- == 1` (or 
rather `--(*count) == 0`), which would indicate that there are no AIO 
functions still in flight?

Max

> Reported-by: Coverity (CID 1451082)
> Fixes: dc04d25e2f3f ("hw/block/nvme: add support for the format nvm command")
> Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
> ---
>   hw/block/nvme.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> index 6842b01ab58b..dad275971a84 100644
> --- a/hw/block/nvme.c
> +++ b/hw/block/nvme.c
> @@ -4984,6 +4984,11 @@ static uint16_t nvme_format_ns(NvmeCtrl *n, NvmeNamespace *ns, uint8_t lbaf,
>       ns->status = NVME_FORMAT_IN_PROGRESS;
>   
>       len = ns->size;
> +
> +    if (!len) {
> +        return NVME_SUCCESS;
> +    }
> +
>       offset = 0;
>   
>       count = g_new(int, 1);
> 

On Mar 22 11:02, Max Reitz wrote:
> On 22.03.21 07:19, Klaus Jensen wrote:
> > From: Klaus Jensen <k.jensen@samsung.com>
> > 
> > In nvme_format_ns(), if the namespace is of zero size (which might be
> > useless, but not invalid), the `count` variable will leak. Fix this by
> > returning early in that case.
> 
> When looking at the Coverity report, something else caught my eye: As far as
> I’m aware, blk_aio_pwrite_zeroes() may invoke the CB before returning (if
> blk_do_pwritev_part() returns without yielding).  I don’t think that will
> happen with real hardware (who knows, though), but it should be possible to
> see with the null-co block driver.
> 
> nvme_format_ns() doesn’t quite look like it takes that into account. For
> example, because *count starts at 1 and is decremented after the while (len)
> loop, all nvme_aio_format_cb() invocations (if they are invoked before their
> blk_aio_pwrite_zeroes() returns) will see
> *count == 2, and thus not free it, or call nvme_enqueue_req_completion().
> 
> I don’t know whether the latter is problematic, but not freeing `count`
> doesn’t seem right.  Perhaps this could be addressed by adding a condition
> to the `(*count)--` to see whether `(*count)-- == 1` (or rather `--(*count)
> == 0`), which would indicate that there are no AIO functions still in
> flight?

Hi Max,

Thanks for glossing over this.

And, yeah, you are right, nice catch. The reference counting is exactly
to guard against pwrite_zeroes invoking the CB before returning, but if
it happens it is not correctly handling it anyway :(

This stuff is exactly why I proposed converting all this into the
"proper" BlockAIOCB approach (see [1]), but it need a little more work.

I'll v2 this with a fix for this! Thanks!


  [1]: https://lore.kernel.org/qemu-devel/20210302111040.289244-1-its@irrelevant.dk/

On 22.03.21 11:48, Klaus Jensen wrote:
> On Mar 22 11:02, Max Reitz wrote:
>> On 22.03.21 07:19, Klaus Jensen wrote:
>>> From: Klaus Jensen <k.jensen@samsung.com>
>>>
>>> In nvme_format_ns(), if the namespace is of zero size (which might be
>>> useless, but not invalid), the `count` variable will leak. Fix this by
>>> returning early in that case.
>>
>> When looking at the Coverity report, something else caught my eye: As far as
>> I’m aware, blk_aio_pwrite_zeroes() may invoke the CB before returning (if
>> blk_do_pwritev_part() returns without yielding).  I don’t think that will
>> happen with real hardware (who knows, though), but it should be possible to
>> see with the null-co block driver.
>>
>> nvme_format_ns() doesn’t quite look like it takes that into account. For
>> example, because *count starts at 1 and is decremented after the while (len)
>> loop, all nvme_aio_format_cb() invocations (if they are invoked before their
>> blk_aio_pwrite_zeroes() returns) will see
>> *count == 2, and thus not free it, or call nvme_enqueue_req_completion().
>>
>> I don’t know whether the latter is problematic, but not freeing `count`
>> doesn’t seem right.  Perhaps this could be addressed by adding a condition
>> to the `(*count)--` to see whether `(*count)-- == 1` (or rather `--(*count)
>> == 0`), which would indicate that there are no AIO functions still in
>> flight?
> 
> Hi Max,
> 
> Thanks for glossing over this.
> 
> And, yeah, you are right, nice catch. The reference counting is exactly
> to guard against pwrite_zeroes invoking the CB before returning, but if
> it happens it is not correctly handling it anyway :(
> 
> This stuff is exactly why I proposed converting all this into the
> "proper" BlockAIOCB approach (see [1]), but it need a little more work.
> 
> I'll v2 this with a fix for this! Thanks!
> 
> 
>    [1]: https://lore.kernel.org/qemu-devel/20210302111040.289244-1-its@irrelevant.dk/

OK, thanks! :)

That rewrite does look more in-line with how AIO is handled elsewhere, yes.

Max