[PATCH] staging: vchiq_arm: cast with __force as needed

[PATCH] staging: vchiq_arm: cast with __force as needed

[Mitchell Tasman]

In several cases where a pointer marked as __user is
(intentionally) assigned or passed to a non-marked target,
cast to the target pointer type with a __force directive
to quiet warnings from sparse.

Signed-off-by: Mitchell Tasman <tasman@leaflabs.com>
---
 .../vc04_services/interface/vchiq_arm/vchiq_2835_arm.c     | 7 ++++---
 .../staging/vc04_services/interface/vchiq_arm/vchiq_arm.c  | 4 +++-
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
index c18c6ca0b6c0..38a13e4618a8 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
@@ -371,14 +371,15 @@ create_pagelist(char __user *buf, size_t count, unsigned short type)
 	pagelistinfo->scatterlist = scatterlist;
 	pagelistinfo->scatterlist_mapped = 0;
 
-	if (is_vmalloc_addr(buf)) {
+	if (is_vmalloc_addr((void __force *)buf)) {
 		unsigned long length = count;
 		unsigned int off = offset;
 
 		for (actual_pages = 0; actual_pages < num_pages;
 		     actual_pages++) {
-			struct page *pg = vmalloc_to_page(buf + (actual_pages *
-								 PAGE_SIZE));
+			struct page *pg =
+				vmalloc_to_page((void __force *)(buf +
+						 (actual_pages * PAGE_SIZE)));
 			size_t bytes = PAGE_SIZE - off;
 
 			if (!pg) {
diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
index 2d3e114f4a66..28ea8c3a4cba 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
@@ -1209,7 +1209,9 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 					/* The completion must point to the
 					** msgbuf. */
-					completion->header = msgbuf;
+					completion->header =
+						(struct vchiq_header __force *)
+						msgbuf;
 				}
 
 				if ((completion->reason ==
-- 
2.17.1

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Re: [PATCH] staging: vchiq_arm: cast with __force as needed

[Dan Carpenter]

On Mon, May 18, 2020 at 08:45:31PM -0400, Mitchell Tasman wrote:
> In several cases where a pointer marked as __user is
> (intentionally) assigned or passed to a non-marked target,
> cast to the target pointer type with a __force directive
> to quiet warnings from sparse.
> 
> Signed-off-by: Mitchell Tasman <tasman@leaflabs.com>
> ---
>  .../vc04_services/interface/vchiq_arm/vchiq_2835_arm.c     | 7 ++++---
>  .../staging/vc04_services/interface/vchiq_arm/vchiq_arm.c  | 4 +++-
>  2 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
> index c18c6ca0b6c0..38a13e4618a8 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
> @@ -371,14 +371,15 @@ create_pagelist(char __user *buf, size_t count, unsigned short type)
>  	pagelistinfo->scatterlist = scatterlist;
>  	pagelistinfo->scatterlist_mapped = 0;
>  
> -	if (is_vmalloc_addr(buf)) {
> +	if (is_vmalloc_addr((void __force *)buf)) {

Am I reading this correctly???

This is actually a user controlled pointer that comes from the
vchiq_ioctl() when we do VCHIQ_IOC_QUEUE_BULK_TRANSMIT/RECEIVE.  So we
take random pointer from user space and if it happens to point to kernel
space then we trust it and presumably start BULK_TRANSMITing data to
it???

LOL....  This doesn't seem safe at all.

regards,
dan carpenter

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Re: [PATCH] staging: vchiq_arm: cast with __force as needed

[Mitchell Tasman]

On 5/22/20 7:06 AM, Dan Carpenter wrote:
> On Mon, May 18, 2020 at 08:45:31PM -0400, Mitchell Tasman wrote:
>> In several cases where a pointer marked as __user is
>> (intentionally) assigned or passed to a non-marked target,
>> cast to the target pointer type with a __force directive
>> to quiet warnings from sparse.
>>
>> Signed-off-by: Mitchell Tasman <tasman@leaflabs.com>
>> ---
>>  .../vc04_services/interface/vchiq_arm/vchiq_2835_arm.c     | 7 ++++---
>>  .../staging/vc04_services/interface/vchiq_arm/vchiq_arm.c  | 4 +++-
>>  2 files changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
>> index c18c6ca0b6c0..38a13e4618a8 100644
>> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
>> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
>> @@ -371,14 +371,15 @@ create_pagelist(char __user *buf, size_t count, unsigned short type)
>>  	pagelistinfo->scatterlist = scatterlist;
>>  	pagelistinfo->scatterlist_mapped = 0;
>>  
>> -	if (is_vmalloc_addr(buf)) {
>> +	if (is_vmalloc_addr((void __force *)buf)) {
> 
> Am I reading this correctly???
> 
> This is actually a user controlled pointer that comes from the
> vchiq_ioctl() when we do VCHIQ_IOC_QUEUE_BULK_TRANSMIT/RECEIVE.  So we
> take random pointer from user space and if it happens to point to kernel
> space then we trust it and presumably start BULK_TRANSMITing data to
> it???
> 
> LOL....  This doesn't seem safe at all.

Is additional validation of buf and its extent necessary and sufficient, e.g. perhaps access_ok(buf, count * PAGE_SIZE) somewhere along the call chain?  Or does vhciq_arm need to take a different approach in the area that Dan Carpenter flagged?

Thank you.

> 
> regards,
> dan carpenter
> 

Regards,
Mitch
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