[PULL,07/11] vfio: Fix null pointer dereference bug in vfio_bars_finalize()

Commit Message

Cédric Le Goater July 10, 2023, 7:48 a.m. UTC

From: Avihai Horon <[e-mail]>

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 <[e-mail]>
Reviewed-by: Philippe Mathieu-Daudé <[e-mail]>
Reviewed-by: Cédric Le Goater <[e-mail]>
Reviewed-by: Alex Williamson <[e-mail]>
Signed-off-by: Cédric Le Goater <[e-mail]>
---
 hw/vfio/pci.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Michael Tokarev July 10, 2023, 2:36 p.m. UTC | #1

10.07.2023 10:48, Cédric Le Goater пишет:
> From: Avihai Horon <[e-mail]>
> 
> 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 <[e-mail]>

It looks like it's a -stable material too. Queued this one.
If it shouldn't go to stable, please let me know.

Thanks,

/mjt

Patch

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 68dd99283620..c89fdf7ae6c2 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;
         }
     }