[PATCH next] dma-buf/sync-file: do not allow zero size allocations

[PATCH next] dma-buf/sync-file: do not allow zero size allocations

[Pavel Skripkin]

syzbot reported GPF in dma_fence_array_first(), which is caused by
dereferencing ZERO_PTR in dma-buf internals.

ZERO_PTR was generated in sync_file_merge(). This functuion tries to
reduce allocation size, but does not check if it reducing to 0.

Fix reported bug by validating `index` value before passing it to
krealloc_array().

Fail log:

general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
CPU: 1 PID: 3595 Comm: syz-executor814 Not tainted 5.17.0-next-20220328-syzkaller #0
...
RIP: 0010:dma_fence_array_first+0x78/0xb0 drivers/dma-buf/dma-fence-array.c:234
...
Call Trace:
 <TASK>
 __dma_fence_unwrap_array include/linux/dma-fence-unwrap.h:42 [inline]
 dma_fence_unwrap_first include/linux/dma-fence-unwrap.h:57 [inline]
 sync_file_ioctl_fence_info drivers/dma-buf/sync_file.c:414 [inline]
 sync_file_ioctl+0x248/0x22c0 drivers/dma-buf/sync_file.c:477
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]

There was same problem with initial kcalloc() allocation in same
function, so it's fixed as well.

Reported-and-tested-by: syzbot+5c943fe38e86d615cac2@syzkaller.appspotmail.com
Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---
 drivers/dma-buf/sync_file.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index b8dea4ec123b..aa744f017008 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -212,7 +212,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 	dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
 		++num_fences;
 
-	if (num_fences > INT_MAX)
+	if (num_fences > INT_MAX || !num_fences)
 		goto err_free_sync_file;
 
 	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
@@ -264,7 +264,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 	if (index == 0)
 		add_fence(fences, &index, dma_fence_get_stub());
 
-	if (num_fences > index) {
+	if (index && num_fences > index) {
 		struct dma_fence **tmp;
 
 		/* Keep going even when reducing the size failed */
-- 
2.35.1

Re: [Linaro-mm-sig] [PATCH next] dma-buf/sync-file: do not allow zero size allocations

[Christian König]

That problem is already fixed with patch 21d139d73f77 dma-buf/sync-file: 
fix logic error in new fence merge code.

Am 30.03.22 um 00:14 schrieb Pavel Skripkin:
> syzbot reported GPF in dma_fence_array_first(), which is caused by
> dereferencing ZERO_PTR in dma-buf internals.
>
> ZERO_PTR was generated in sync_file_merge(). This functuion tries to
> reduce allocation size, but does not check if it reducing to 0.

This is actually perfectly ok. The code above should have prevented the 
size to become 0.

Regards,
Christian.

>
> Fix reported bug by validating `index` value before passing it to
> krealloc_array().
>
> Fail log:
>
> general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
> CPU: 1 PID: 3595 Comm: syz-executor814 Not tainted 5.17.0-next-20220328-syzkaller #0
> ...
> RIP: 0010:dma_fence_array_first+0x78/0xb0 drivers/dma-buf/dma-fence-array.c:234
> ...
> Call Trace:
>   <TASK>
>   __dma_fence_unwrap_array include/linux/dma-fence-unwrap.h:42 [inline]
>   dma_fence_unwrap_first include/linux/dma-fence-unwrap.h:57 [inline]
>   sync_file_ioctl_fence_info drivers/dma-buf/sync_file.c:414 [inline]
>   sync_file_ioctl+0x248/0x22c0 drivers/dma-buf/sync_file.c:477
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   __do_sys_ioctl fs/ioctl.c:870 [inline]
>
> There was same problem with initial kcalloc() allocation in same
> function, so it's fixed as well.
>
> Reported-and-tested-by: syzbot+5c943fe38e86d615cac2@syzkaller.appspotmail.com
> Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
> ---
>   drivers/dma-buf/sync_file.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index b8dea4ec123b..aa744f017008 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -212,7 +212,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>   	dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
>   		++num_fences;
>   
> -	if (num_fences > INT_MAX)
> +	if (num_fences > INT_MAX || !num_fences)
>   		goto err_free_sync_file;
>   
>   	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
> @@ -264,7 +264,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>   	if (index == 0)
>   		add_fence(fences, &index, dma_fence_get_stub());
>   
> -	if (num_fences > index) {
> +	if (index && num_fences > index) {
>   		struct dma_fence **tmp;
>   
>   		/* Keep going even when reducing the size failed */

Re: [Linaro-mm-sig] [PATCH next] dma-buf/sync-file: do not allow zero size allocations

[Pavel Skripkin]

Hi Christian,

On 3/30/22 10:09, Christian König wrote:
> That problem is already fixed with patch 21d139d73f77 dma-buf/sync-file:
> fix logic error in new fence merge code.
> 
> Am 30.03.22 um 00:14 schrieb Pavel Skripkin:
>> syzbot reported GPF in dma_fence_array_first(), which is caused by
>> dereferencing ZERO_PTR in dma-buf internals.
>>
>> ZERO_PTR was generated in sync_file_merge(). This functuion tries to
>> reduce allocation size, but does not check if it reducing to 0.
> 
> This is actually perfectly ok. The code above should have prevented the
> size to become 0.
> 
> Regards,
> Christian.
> 

Thanks for your reply! I see that 21d139d73f77 fixes GPF in 
dma_fence_array_first(), but what about this part:

>>   
>> -	if (num_fences > INT_MAX)
>> +	if (num_fences > INT_MAX || !num_fences)
>>   		goto err_free_sync_file;
>>   
>>   	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
>> @@ -264,7 +264,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>>   	if (index == 0)

If num_fences is equal to zero then fences dereference will cause an 
oops. Or this one is also fixed in your tree?


Thanks!




With regards,
Pavel Skripkin

Re: [Linaro-mm-sig] [PATCH next] dma-buf/sync-file: do not allow zero size allocations

[Christian König]

Am 30.03.22 um 20:24 schrieb Pavel Skripkin:
> Hi Christian,
>
> On 3/30/22 10:09, Christian König wrote:
>> That problem is already fixed with patch 21d139d73f77 dma-buf/sync-file:
>> fix logic error in new fence merge code.
>>
>> Am 30.03.22 um 00:14 schrieb Pavel Skripkin:
>>> syzbot reported GPF in dma_fence_array_first(), which is caused by
>>> dereferencing ZERO_PTR in dma-buf internals.
>>>
>>> ZERO_PTR was generated in sync_file_merge(). This functuion tries to
>>> reduce allocation size, but does not check if it reducing to 0.
>>
>> This is actually perfectly ok. The code above should have prevented the
>> size to become 0.
>>
>> Regards,
>> Christian.
>>
>
> Thanks for your reply! I see that 21d139d73f77 fixes GPF in 
> dma_fence_array_first(), but what about this part:
>
>>>   -    if (num_fences > INT_MAX)
>>> +    if (num_fences > INT_MAX || !num_fences)
>>>           goto err_free_sync_file;
>>>         fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
>>> @@ -264,7 +264,7 @@ static struct sync_file *sync_file_merge(const 
>>> char *name, struct sync_file *a,
>>>       if (index == 0)
>
> If num_fences is equal to zero then fences dereference will cause an 
> oops. Or this one is also fixed in your tree?

Well it is illegal for sync_file->fence to be NULL or we would run into 
NULL pointer dereference much more often, so num_fences can't be zero 
here either.

Regards,
Christian.

>
>
> Thanks!
>
>
>
>
> With regards,
> Pavel Skripkin

[PATCH next v2] dma-buf/sync-file: do not allow zero size allocation

[Pavel Skripkin]

num_fences is user-controlled value and it can be equal to 0. Code
should not pass 0 to kcalloc(), since it will cause kcalloc() to return
ZERO_PTR. ZERO_PTR will pass `!fences` check and kernel will panic
because of dereferencing ZERO_PTR in add_fence()

Fix it by validating num_fences and bail out early if it is equal to 0

Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---

Changes since v1:
	- Dropped already merged part
	- Removed syzkaller's tag

---
 drivers/dma-buf/sync_file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index b8dea4ec123b..024f22193e0c 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -212,7 +212,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 	dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
 		++num_fences;
 
-	if (num_fences > INT_MAX)
+	if (num_fences > INT_MAX || !num_fences)
 		goto err_free_sync_file;
 
 	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
-- 
2.35.1

Re: [PATCH next v2] dma-buf/sync-file: do not allow zero size allocation

[Christian König]

Am 01.04.22 um 23:31 schrieb Pavel Skripkin:
> num_fences is user-controlled value and it can be equal to 0. Code
> should not pass 0 to kcalloc(), since it will cause kcalloc() to return
> ZERO_PTR. ZERO_PTR will pass `!fences` check and kernel will panic
> because of dereferencing ZERO_PTR in add_fence()
>
> Fix it by validating num_fences and bail out early if it is equal to 0

Well there are multiple issues with this patch. First of all as I wrote 
before it shouldn't be possible that num_fences is zero.

We could still just add this as a precaution, but then bailing out is 
the wrong thing to do here. Instead we should then make sure to allocate 
at least one slot for a fence in the array.

But I think the cleanest would just be to not add a fence into the array 
in the first place when num_fences is zero.

Regards,
Christian.

>
> Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
> ---
>
> Changes since v1:
> 	- Dropped already merged part
> 	- Removed syzkaller's tag
>
> ---
>   drivers/dma-buf/sync_file.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index b8dea4ec123b..024f22193e0c 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -212,7 +212,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>   	dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
>   		++num_fences;
>   
> -	if (num_fences > INT_MAX)
> +	if (num_fences > INT_MAX || !num_fences)
>   		goto err_free_sync_file;
>   
>   	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);