2020-05-22 01:22:54

by Qian Cai

Subject: [PATCH -next] vfio/pci: fix a null-ptr-deref in vfio_config_free()

It is possible vfio_config_init() does not call vfio_cap_len(), and then
vdev->msi_perm == NULL. Later, in vfio_config_free(), it could trigger a
null-ptr-deref.

BUG: kernel NULL pointer dereference, address: 0000000000000000
RIP: 0010:vfio_config_free+0x7a/0xe0 [vfio_pci]
vfio_config_free+0x7a/0xe0:
free_perm_bits at drivers/vfio/pci/vfio_pci_config.c:340
(inlined by) vfio_config_free at drivers/vfio/pci/vfio_pci_config.c:1760
Call Trace:
vfio_pci_release+0x3a4/0x9e0 [vfio_pci]
vfio_device_fops_release+0x50/0x80 [vfio]
__fput+0x200/0x460
____fput+0xe/0x10
task_work_run+0x127/0x1b0
do_exit+0x782/0x10d0
do_group_exit+0xc7/0x1c0
__x64_sys_exit_group+0x2c/0x30
do_syscall_64+0x64/0x350
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: bea890bdb161 ("vfio/pci: fix memory leaks in alloc_perm_bits()")
Signed-off-by: Qian Cai <[email protected]>
---
drivers/vfio/pci/vfio_pci_config.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index d127a0c50940..8746c943247a 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -1757,9 +1757,11 @@ void vfio_config_free(struct vfio_pci_device *vdev)
vdev->vconfig = NULL;
kfree(vdev->pci_config_map);
vdev->pci_config_map = NULL;
- free_perm_bits(vdev->msi_perm);
- kfree(vdev->msi_perm);
- vdev->msi_perm = NULL;
+ if (vdev->msi_perm) {
+ free_perm_bits(vdev->msi_perm);
+ kfree(vdev->msi_perm);
+ vdev->msi_perm = NULL;
+ }
}

/*
--
2.17.2 (Apple Git-113)

2020-05-26 16:24:09

by Alex Williamson

Subject: Re: [PATCH -next] vfio/pci: fix a null-ptr-deref in vfio_config_free()

On Thu, 21 May 2020 21:18:29 -0400
Qian Cai <[email protected]> wrote:

> It is possible vfio_config_init() does not call vfio_cap_len(), and then
> vdev->msi_perm == NULL. Later, in vfio_config_free(), it could trigger a
> null-ptr-deref.
>
> BUG: kernel NULL pointer dereference, address: 0000000000000000
> RIP: 0010:vfio_config_free+0x7a/0xe0 [vfio_pci]
> vfio_config_free+0x7a/0xe0:
> free_perm_bits at drivers/vfio/pci/vfio_pci_config.c:340
> (inlined by) vfio_config_free at drivers/vfio/pci/vfio_pci_config.c:1760
> Call Trace:
> vfio_pci_release+0x3a4/0x9e0 [vfio_pci]
> vfio_device_fops_release+0x50/0x80 [vfio]
> __fput+0x200/0x460
> ____fput+0xe/0x10
> task_work_run+0x127/0x1b0
> do_exit+0x782/0x10d0
> do_group_exit+0xc7/0x1c0
> __x64_sys_exit_group+0x2c/0x30
> do_syscall_64+0x64/0x350
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Fixes: bea890bdb161 ("vfio/pci: fix memory leaks in alloc_perm_bits()")
> Signed-off-by: Qian Cai <[email protected]>
> ---
> drivers/vfio/pci/vfio_pci_config.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)

I may get yelled at for it, but I need to break my next branch to fix
the lockdep issue you noted in my series, so I'm going to go ahead and
roll this into your previous patch. Thanks,

Alex

> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index d127a0c50940..8746c943247a 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -1757,9 +1757,11 @@ void vfio_config_free(struct vfio_pci_device *vdev)
> vdev->vconfig = NULL;
> kfree(vdev->pci_config_map);
> vdev->pci_config_map = NULL;
> - free_perm_bits(vdev->msi_perm);
> - kfree(vdev->msi_perm);
> - vdev->msi_perm = NULL;
> + if (vdev->msi_perm) {
> + free_perm_bits(vdev->msi_perm);
> + kfree(vdev->msi_perm);
> + vdev->msi_perm = NULL;
> + }
> }
>
> /*