[v2] vfio: Fix null pointer dereference bug in vfio_bars_finalize()

[PATCH v2] vfio: Fix null pointer dereference bug in vfio_bars_finalize()

Posted by Avihai Horon 9 months, 4 weeks ago

vfio_realize() has the following flow:
1. vfio_bars_prepare() -- sets VFIOBAR->size.
2. msix_early_setup().
3. vfio_bars_register() -- allocates VFIOBAR->mr.

After vfio_bars_prepare() is called msix_early_setup() can fail. If it
does fail, vfio_bars_register() is never called and VFIOBAR->mr is not
allocated.

In this case, vfio_bars_finalize() is called as part of the error flow
to free the bars' resources. However, vfio_bars_finalize() calls
object_unparent() for VFIOBAR->mr after checking only VFIOBAR->size, and
thus we get a null pointer dereference.

Fix it by checking VFIOBAR->mr in vfio_bars_finalize().

Fixes: 89d5202edc50 ("vfio/pci: Allow relocating MSI-X MMIO")
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---

 Changes from v1:
 * Assert VFIOBAR->size and set VFIOBAR->mr to NULL to make the code
   more accurate. (Philippe)
 * Small reword in the last paragraph of the commit message.

 hw/vfio/pci.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index ab6645ba60..bc98791cbb 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -1752,9 +1752,11 @@ static void vfio_bars_finalize(VFIOPCIDevice *vdev)
 
         vfio_bar_quirk_finalize(vdev, i);
         vfio_region_finalize(&bar->region);
-        if (bar->size) {
+        if (bar->mr) {
+            assert(bar->size);
             object_unparent(OBJECT(bar->mr));
             g_free(bar->mr);
+            bar->mr = NULL;
         }
     }
 
-- 
2.26.3

Re: [PATCH v2] vfio: Fix null pointer dereference bug in vfio_bars_finalize()

Posted by Alex Williamson 9 months, 3 weeks ago

On Tue, 4 Jul 2023 16:39:27 +0300
Avihai Horon <avihaih@nvidia.com> wrote:

> vfio_realize() has the following flow:
> 1. vfio_bars_prepare() -- sets VFIOBAR->size.
> 2. msix_early_setup().
> 3. vfio_bars_register() -- allocates VFIOBAR->mr.
> 
> After vfio_bars_prepare() is called msix_early_setup() can fail. If it
> does fail, vfio_bars_register() is never called and VFIOBAR->mr is not
> allocated.
> 
> In this case, vfio_bars_finalize() is called as part of the error flow
> to free the bars' resources. However, vfio_bars_finalize() calls
> object_unparent() for VFIOBAR->mr after checking only VFIOBAR->size, and
> thus we get a null pointer dereference.
> 
> Fix it by checking VFIOBAR->mr in vfio_bars_finalize().
> 
> Fixes: 89d5202edc50 ("vfio/pci: Allow relocating MSI-X MMIO")
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
> ---
> 
>  Changes from v1:
>  * Assert VFIOBAR->size and set VFIOBAR->mr to NULL to make the code
>    more accurate. (Philippe)
>  * Small reword in the last paragraph of the commit message.
> 
>  hw/vfio/pci.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index ab6645ba60..bc98791cbb 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -1752,9 +1752,11 @@ static void vfio_bars_finalize(VFIOPCIDevice *vdev)
>  
>          vfio_bar_quirk_finalize(vdev, i);
>          vfio_region_finalize(&bar->region);
> -        if (bar->size) {
> +        if (bar->mr) {
> +            assert(bar->size);
>              object_unparent(OBJECT(bar->mr));
>              g_free(bar->mr);
> +            bar->mr = NULL;
>          }
>      }
>  

Reviewed-by: Alex Williamson <alex.williamson@redhat.com>

Re: [PATCH v2] vfio: Fix null pointer dereference bug in vfio_bars_finalize()

Posted by Cédric Le Goater 9 months, 4 weeks ago

Hello Avihai

On 7/4/23 15:39, Avihai Horon wrote:
> vfio_realize() has the following flow:
> 1. vfio_bars_prepare() -- sets VFIOBAR->size.
> 2. msix_early_setup().
> 3. vfio_bars_register() -- allocates VFIOBAR->mr.
> 
> After vfio_bars_prepare() is called msix_early_setup() can fail. If it
> does fail, vfio_bars_register() is never called and VFIOBAR->mr is not
> allocated.
> 
> In this case, vfio_bars_finalize() is called as part of the error flow
> to free the bars' resources. However, vfio_bars_finalize() calls
> object_unparent() for VFIOBAR->mr after checking only VFIOBAR->size, and
> thus we get a null pointer dereference.
> 
> Fix it by checking VFIOBAR->mr in vfio_bars_finalize().

Did you see the issue by reading the code or did you actually crash
QEMU with a test case ?

> 
> Fixes: 89d5202edc50 ("vfio/pci: Allow relocating MSI-X MMIO")
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>


Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.


> ---
> 
>   Changes from v1:
>   * Assert VFIOBAR->size and set VFIOBAR->mr to NULL to make the code
>     more accurate. (Philippe)
>   * Small reword in the last paragraph of the commit message.
> 
>   hw/vfio/pci.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index ab6645ba60..bc98791cbb 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -1752,9 +1752,11 @@ static void vfio_bars_finalize(VFIOPCIDevice *vdev)
>   
>           vfio_bar_quirk_finalize(vdev, i);
>           vfio_region_finalize(&bar->region);
> -        if (bar->size) {
> +        if (bar->mr) {
> +            assert(bar->size);
>               object_unparent(OBJECT(bar->mr));
>               g_free(bar->mr);
> +            bar->mr = NULL;
>           }
>       }
>

Re: [PATCH v2] vfio: Fix null pointer dereference bug in vfio_bars_finalize()

Posted by Avihai Horon 9 months, 4 weeks ago

On 04/07/2023 18:54, Cédric Le Goater wrote:
> External email: Use caution opening links or attachments
>
>
> Hello Avihai
>
> On 7/4/23 15:39, Avihai Horon wrote:
>> vfio_realize() has the following flow:
>> 1. vfio_bars_prepare() -- sets VFIOBAR->size.
>> 2. msix_early_setup().
>> 3. vfio_bars_register() -- allocates VFIOBAR->mr.
>>
>> After vfio_bars_prepare() is called msix_early_setup() can fail. If it
>> does fail, vfio_bars_register() is never called and VFIOBAR->mr is not
>> allocated.
>>
>> In this case, vfio_bars_finalize() is called as part of the error flow
>> to free the bars' resources. However, vfio_bars_finalize() calls
>> object_unparent() for VFIOBAR->mr after checking only VFIOBAR->size, and
>> thus we get a null pointer dereference.
>>
>> Fix it by checking VFIOBAR->mr in vfio_bars_finalize().
>
> Did you see the issue by reading the code or did you actually crash
> QEMU with a test case ?

I actually got a segmentation fault after msix_early_setup() failed (due 
to some other misconfiguration from my side).

>
>>
>> Fixes: 89d5202edc50 ("vfio/pci: Allow relocating MSI-X MMIO")
>> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
>
>
> Reviewed-by: Cédric Le Goater <clg@redhat.com>
>
> Thanks,
>
> C.
>
>
>> ---
>>
>>   Changes from v1:
>>   * Assert VFIOBAR->size and set VFIOBAR->mr to NULL to make the code
>>     more accurate. (Philippe)
>>   * Small reword in the last paragraph of the commit message.
>>
>>   hw/vfio/pci.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
>> index ab6645ba60..bc98791cbb 100644
>> --- a/hw/vfio/pci.c
>> +++ b/hw/vfio/pci.c
>> @@ -1752,9 +1752,11 @@ static void vfio_bars_finalize(VFIOPCIDevice 
>> *vdev)
>>
>>           vfio_bar_quirk_finalize(vdev, i);
>>           vfio_region_finalize(&bar->region);
>> -        if (bar->size) {
>> +        if (bar->mr) {
>> +            assert(bar->size);
>>               object_unparent(OBJECT(bar->mr));
>>               g_free(bar->mr);
>> +            bar->mr = NULL;
>>           }
>>       }
>>
>

Re: [PATCH v2] vfio: Fix null pointer dereference bug in vfio_bars_finalize()

Posted by Philippe Mathieu-Daudé 9 months, 4 weeks ago

On 4/7/23 15:39, Avihai Horon wrote:
> vfio_realize() has the following flow:
> 1. vfio_bars_prepare() -- sets VFIOBAR->size.
> 2. msix_early_setup().
> 3. vfio_bars_register() -- allocates VFIOBAR->mr.
> 
> After vfio_bars_prepare() is called msix_early_setup() can fail. If it
> does fail, vfio_bars_register() is never called and VFIOBAR->mr is not
> allocated.
> 
> In this case, vfio_bars_finalize() is called as part of the error flow
> to free the bars' resources. However, vfio_bars_finalize() calls
> object_unparent() for VFIOBAR->mr after checking only VFIOBAR->size, and
> thus we get a null pointer dereference.
> 
> Fix it by checking VFIOBAR->mr in vfio_bars_finalize().
> 
> Fixes: 89d5202edc50 ("vfio/pci: Allow relocating MSI-X MMIO")
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
> ---
> 
>   Changes from v1:
>   * Assert VFIOBAR->size and set VFIOBAR->mr to NULL to make the code
>     more accurate. (Philippe)
>   * Small reword in the last paragraph of the commit message.
> 
>   hw/vfio/pci.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>