[PATCH v2] misc: fastrpc: Fix incorrect DMA mapping unmap request

[PATCH v2] misc: fastrpc: Fix incorrect DMA mapping unmap request

[Ekansh Gupta]

Scatterlist table is obtained during map create request and the same
table is used for DMA mapping unmap. In case there is any failure
while getting the sg_table, ERR_PTR is returned instead of sg_table.

When the map is getting freed, there is only a non-NULL check of
sg_table which will also be true in case failure was returned instead
of sg_table. This would result in improper unmap request. Add proper
check to avoid bad unmap request.

Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
Cc: stable <stable@kernel.org>
Tested-by: Ekansh Gupta <quic_ekangupt@quicinc.com>
Signed-off-by: Ekansh Gupta <quic_ekangupt@quicinc.com>
---
Changes in v2:
  - Added fixes information to commit text

 drivers/misc/fastrpc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 9666d28..75da69a 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -313,7 +313,7 @@ static void fastrpc_free_map(struct kref *ref)
 
 	map = container_of(ref, struct fastrpc_map, refcount);
 
-	if (map->table) {
+	if (map->table && !IS_ERR(map->table)) {
 		if (map->attr & FASTRPC_ATTR_SECUREMAP) {
 			struct qcom_scm_vmperm perm;
 			int vmid = map->fl->cctx->vmperms[0].vmid;
-- 
2.7.4

Re: [PATCH v2] misc: fastrpc: Fix incorrect DMA mapping unmap request

[Bjorn Andersson]

On Mon, Jul 24, 2023 at 12:39:31PM +0530, Ekansh Gupta wrote:
> Scatterlist table is obtained during map create request and the same

I'm guessing that this all happens in fastrpc_map_create() where:

  map->table = dma_buf_map_attachment_unlocked(map->attach, DMA_BIDIRECTIONAL);

fails, we jump to map_err, and then call fastrpc_map_put(map), which
then ends up in the code below?

> table is used for DMA mapping unmap. In case there is any failure
> while getting the sg_table, ERR_PTR is returned instead of sg_table.

The problem isn't that ERR_PTR() is being returned, the problem is that
this is being assigned to map->table and you keep running.

> 
> When the map is getting freed, there is only a non-NULL check of
> sg_table which will also be true in case failure was returned instead
> of sg_table. This would result in improper unmap request. Add proper
> check to avoid bad unmap request.
> 
> Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
> Cc: stable <stable@kernel.org>
> Tested-by: Ekansh Gupta <quic_ekangupt@quicinc.com>

You always test your own patches, so no need to declare this.

> Signed-off-by: Ekansh Gupta <quic_ekangupt@quicinc.com>
> ---
> Changes in v2:
>   - Added fixes information to commit text
> 
>  drivers/misc/fastrpc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 9666d28..75da69a 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -313,7 +313,7 @@ static void fastrpc_free_map(struct kref *ref)
>  
>  	map = container_of(ref, struct fastrpc_map, refcount);
>  
> -	if (map->table) {
> +	if (map->table && !IS_ERR(map->table)) {

Rather than carrying around an IS_ERR(map->table), I think you should
address this at the originating place. E.g. assign the return value of
the dma_buf_map_attachment_unlocked() to a local variable and only if it
is valid you assign map->table. Or perhaps make it NULL in the error
path.

Regards,
Bjorn

>  		if (map->attr & FASTRPC_ATTR_SECUREMAP) {
>  			struct qcom_scm_vmperm perm;
>  			int vmid = map->fl->cctx->vmperms[0].vmid;
> -- 
> 2.7.4
> 

Re: [PATCH v2] misc: fastrpc: Fix incorrect DMA mapping unmap request

[Ekansh Gupta]

On 7/26/2023 12:00 PM, Bjorn Andersson wrote:
> On Mon, Jul 24, 2023 at 12:39:31PM +0530, Ekansh Gupta wrote:
>> Scatterlist table is obtained during map create request and the same
> 
> I'm guessing that this all happens in fastrpc_map_create() where:
> 
>    map->table = dma_buf_map_attachment_unlocked(map->attach, DMA_BIDIRECTIONAL);
> 
> fails, we jump to map_err, and then call fastrpc_map_put(map), which
> then ends up in the code below?
> 
yes, your understanding is correct.
>> table is used for DMA mapping unmap. In case there is any failure
>> while getting the sg_table, ERR_PTR is returned instead of sg_table.
> 
> The problem isn't that ERR_PTR() is being returned, the problem is that
> this is being assigned to map->table and you keep running.
> 
>>
>> When the map is getting freed, there is only a non-NULL check of
>> sg_table which will also be true in case failure was returned instead
>> of sg_table. This would result in improper unmap request. Add proper
>> check to avoid bad unmap request.
>>
>> Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
>> Cc: stable <stable@kernel.org>
>> Tested-by: Ekansh Gupta <quic_ekangupt@quicinc.com>
> 
> You always test your own patches, so no need to declare this.
> 
sure, I'll avoid adding this for future changes.
>> Signed-off-by: Ekansh Gupta <quic_ekangupt@quicinc.com>
>> ---
>> Changes in v2:
>>    - Added fixes information to commit text
>>
>>   drivers/misc/fastrpc.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
>> index 9666d28..75da69a 100644
>> --- a/drivers/misc/fastrpc.c
>> +++ b/drivers/misc/fastrpc.c
>> @@ -313,7 +313,7 @@ static void fastrpc_free_map(struct kref *ref)
>>   
>>   	map = container_of(ref, struct fastrpc_map, refcount);
>>   
>> -	if (map->table) {
>> +	if (map->table && !IS_ERR(map->table)) {
> 
> Rather than carrying around an IS_ERR(map->table), I think you should
> address this at the originating place. E.g. assign the return value of
> the dma_buf_map_attachment_unlocked() to a local variable and only if it
> is valid you assign map->table. Or perhaps make it NULL in the error
> path.
> 
understood, this looks much cleaner solution. I'll update this in the 
next patch. Thanks for taking your time to review this change, Bjorn.
--ekansh

> Regards,
> Bjorn
> 
>>   		if (map->attr & FASTRPC_ATTR_SECUREMAP) {
>>   			struct qcom_scm_vmperm perm;
>>   			int vmid = map->fl->cctx->vmperms[0].vmid;
>> -- 
>> 2.7.4
>>