[PATCH] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

[PATCH] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

[Juergen Gross]

The error exit of privcmd_ioctl_dm_op() is calling unlock_pages()
potentially with pages being NULL, leading to a NULL dereference.

Fix that by calling unlock_pages only if lock_pages() was at least
partially successful.

Cc: <stable@vger.kernel.org>
Fixes: ab520be8cd5d ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP")
Reported-by: Rustam Subkhankulov <subkhankulov@ispras.ru>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 drivers/xen/privcmd.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 3369734108af..ec87968b4459 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -679,7 +679,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
 	rc = lock_pages(kbufs, kdata.num, pages, nr_pages, &pinned);
 	if (rc < 0) {
 		nr_pages = pinned;
-		goto out;
+		goto unlock;
 	}
 
 	for (i = 0; i < kdata.num; i++) {
@@ -691,8 +691,9 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
 	rc = HYPERVISOR_dm_op(kdata.dom, kdata.num, xbufs);
 	xen_preemptible_hcall_end();
 
-out:
+ unlock:
 	unlock_pages(pages, nr_pages);
+ out:
 	kfree(xbufs);
 	kfree(pages);
 	kfree(kbufs);
-- 
2.35.3

Re: [PATCH] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

[Oleksandr Tyshchenko]

On 24.08.22 17:26, Juergen Gross wrote:

Hello Juergen

> The error exit of privcmd_ioctl_dm_op() is calling unlock_pages()
> potentially with pages being NULL, leading to a NULL dereference.
>
> Fix that by calling unlock_pages only if lock_pages() was at least
> partially successful.
>
> Cc: <stable@vger.kernel.org>
> Fixes: ab520be8cd5d ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP")
> Reported-by: Rustam Subkhankulov <subkhankulov@ispras.ru>
> Signed-off-by: Juergen Gross <jgross@suse.com>


Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>


> ---
>   drivers/xen/privcmd.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 3369734108af..ec87968b4459 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -679,7 +679,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>   	rc = lock_pages(kbufs, kdata.num, pages, nr_pages, &pinned);
>   	if (rc < 0) {
>   		nr_pages = pinned;
> -		goto out;
> +		goto unlock;
>   	}
>   
>   	for (i = 0; i < kdata.num; i++) {
> @@ -691,8 +691,9 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>   	rc = HYPERVISOR_dm_op(kdata.dom, kdata.num, xbufs);
>   	xen_preemptible_hcall_end();
>   
> -out:
> + unlock:
>   	unlock_pages(pages, nr_pages);
> + out:
>   	kfree(xbufs);
>   	kfree(pages);
>   	kfree(kbufs);

-- 
Regards,

Oleksandr Tyshchenko

Re: [PATCH] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

[Jan Beulich]

On 24.08.2022 16:26, Juergen Gross wrote:
> The error exit of privcmd_ioctl_dm_op() is calling unlock_pages()
> potentially with pages being NULL, leading to a NULL dereference.
> 
> Fix that by calling unlock_pages only if lock_pages() was at least
> partially successful.
> 
> Cc: <stable@vger.kernel.org>
> Fixes: ab520be8cd5d ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP")
> Reported-by: Rustam Subkhankulov <subkhankulov@ispras.ru>
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>
albeit I wonder whether you did consider the variant actually
reducing code size (and avoiding the need for yet another label),
...

> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -679,7 +679,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>  	rc = lock_pages(kbufs, kdata.num, pages, nr_pages, &pinned);
>  	if (rc < 0) {
>  		nr_pages = pinned;

... dropping this line and ...

> -		goto out;
> +		goto unlock;
>  	}
>  
>  	for (i = 0; i < kdata.num; i++) {
> @@ -691,8 +691,9 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>  	rc = HYPERVISOR_dm_op(kdata.dom, kdata.num, xbufs);
>  	xen_preemptible_hcall_end();
>  
> -out:
> + unlock:
>  	unlock_pages(pages, nr_pages);

... passing "pinned" here.

Jan

> + out:
>  	kfree(xbufs);
>  	kfree(pages);
>  	kfree(kbufs);

Re: [PATCH] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

[Juergen Gross]

[-- Attachment #1.1.1: Type: text/plain, Size: 1713 bytes --]

On 25.08.22 09:38, Jan Beulich wrote:
> On 24.08.2022 16:26, Juergen Gross wrote:
>> The error exit of privcmd_ioctl_dm_op() is calling unlock_pages()
>> potentially with pages being NULL, leading to a NULL dereference.
>>
>> Fix that by calling unlock_pages only if lock_pages() was at least
>> partially successful.
>>
>> Cc: <stable@vger.kernel.org>
>> Fixes: ab520be8cd5d ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP")
>> Reported-by: Rustam Subkhankulov <subkhankulov@ispras.ru>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
> 
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> albeit I wonder whether you did consider the variant actually
> reducing code size (and avoiding the need for yet another label),
> ...
> 
>> --- a/drivers/xen/privcmd.c
>> +++ b/drivers/xen/privcmd.c
>> @@ -679,7 +679,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>>   	rc = lock_pages(kbufs, kdata.num, pages, nr_pages, &pinned);
>>   	if (rc < 0) {
>>   		nr_pages = pinned;
> 
> ... dropping this line and ...
> 
>> -		goto out;
>> +		goto unlock;
>>   	}
>>   
>>   	for (i = 0; i < kdata.num; i++) {
>> @@ -691,8 +691,9 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>>   	rc = HYPERVISOR_dm_op(kdata.dom, kdata.num, xbufs);
>>   	xen_preemptible_hcall_end();
>>   
>> -out:
>> + unlock:
>>   	unlock_pages(pages, nr_pages);
> 
> ... passing "pinned" here.

Looking into this I found another problem: NOT using pinned is wrong, as
lock_pages() doesn't guarantee that all pages were really locked. I think
lock_pages() should return an error, in case pin_user_pages_fast() didn't
lock as many pages es expected.


Juergen

[-- Attachment #1.1.2: OpenPGP public key --]
[-- Type: application/pgp-keys, Size: 3149 bytes --]

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 495 bytes --]