[PATCH v2][next] wireless: wext-spy: Fix out-of-bounds warning

[PATCH v2][next] wireless: wext-spy: Fix out-of-bounds warning

[Gustavo A. R. Silva]

Fix the following out-of-bounds warning:

net/wireless/wext-spy.c:178:2: warning: 'memcpy' offset [25, 28] from the object at 'threshold' is out of the bounds of referenced subobject 'low' with type 'struct iw_quality' at offset 20 [-Warray-bounds]

The problem is that the original code is trying to copy data into a
couple of struct members adjacent to each other in a single call to
memcpy(). This causes a legitimate compiler warning because memcpy()
overruns the length of &threshold.low and &spydata->spy_thr_low. As
these are just a couple of struct members, fix this by using direct
assignments, instead of memcpy().

This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().

Link: https://github.com/KSPP/linux/issues/109
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v2:
 - Use direct struct assignments instead of memcpy().
 - Fix one more instance of this same issue in function
   iw_handler_get_thrspy().
 - Update changelog text.
 - Add Kees' RB tag. 

 net/wireless/wext-spy.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/wireless/wext-spy.c b/net/wireless/wext-spy.c
index 33bef22e44e9..b379a0371653 100644
--- a/net/wireless/wext-spy.c
+++ b/net/wireless/wext-spy.c
@@ -120,8 +120,8 @@ int iw_handler_set_thrspy(struct net_device *	dev,
 		return -EOPNOTSUPP;
 
 	/* Just do it */
-	memcpy(&(spydata->spy_thr_low), &(threshold->low),
-	       2 * sizeof(struct iw_quality));
+	spydata->spy_thr_low = threshold->low;
+	spydata->spy_thr_high = threshold->high;
 
 	/* Clear flag */
 	memset(spydata->spy_thr_under, '\0', sizeof(spydata->spy_thr_under));
@@ -147,8 +147,8 @@ int iw_handler_get_thrspy(struct net_device *	dev,
 		return -EOPNOTSUPP;
 
 	/* Just do it */
-	memcpy(&(threshold->low), &(spydata->spy_thr_low),
-	       2 * sizeof(struct iw_quality));
+	threshold->low = spydata->spy_thr_low;
+	threshold->high = spydata->spy_thr_high;
 
 	return 0;
 }
@@ -173,10 +173,10 @@ static void iw_send_thrspy_event(struct net_device *	dev,
 	memcpy(threshold.addr.sa_data, address, ETH_ALEN);
 	threshold.addr.sa_family = ARPHRD_ETHER;
 	/* Copy stats */
-	memcpy(&(threshold.qual), wstats, sizeof(struct iw_quality));
+	threshold.qual = *wstats;
 	/* Copy also thresholds */
-	memcpy(&(threshold.low), &(spydata->spy_thr_low),
-	       2 * sizeof(struct iw_quality));
+	threshold.low = spydata->spy_thr_low;
+	threshold.high = spydata->spy_thr_high;
 
 	/* Send event to user space */
 	wireless_send_event(dev, SIOCGIWTHRSPY, &wrqu, (char *) &threshold);
-- 
2.27.0

Re: [PATCH v2][next] wireless: wext-spy: Fix out-of-bounds warning

[Johannes Berg]

On Thu, 2021-04-22 at 15:00 -0500, Gustavo A. R. Silva wrote:
> 
> Changes in v2:
>  - Use direct struct assignments instead of memcpy().
>  - Fix one more instance of this same issue in function
>    iw_handler_get_thrspy().
>  - Update changelog text.

Thanks.

>  - Add Kees' RB tag. 

He probably won't mind in this case, but you did some pretty substantial
changes to the patch, so I really wouldn't recommend keeping it there.

johannes

Re: [PATCH v2][next] wireless: wext-spy: Fix out-of-bounds warning

[Gustavo A. R. Silva]

On 4/22/21 15:04, Johannes Berg wrote:
> On Thu, 2021-04-22 at 15:00 -0500, Gustavo A. R. Silva wrote:
>>
>> Changes in v2:
>>  - Use direct struct assignments instead of memcpy().
>>  - Fix one more instance of this same issue in function
>>    iw_handler_get_thrspy().
>>  - Update changelog text.
> 
> Thanks.
> 
>>  - Add Kees' RB tag. 
> 
> He probably won't mind in this case, but you did some pretty substantial
> changes to the patch, so I really wouldn't recommend keeping it there.

Right.

Kees, could you please confirm you RB tag in this new version?

Thanks
--
Gustavo

Re: [PATCH v2][next] wireless: wext-spy: Fix out-of-bounds warning

[Kees Cook]

On Thu, Apr 22, 2021 at 10:04:29PM +0200, Johannes Berg wrote:
> On Thu, 2021-04-22 at 15:00 -0500, Gustavo A. R. Silva wrote:
> > 
> > Changes in v2:
> >  - Use direct struct assignments instead of memcpy().
> >  - Fix one more instance of this same issue in function
> >    iw_handler_get_thrspy().
> >  - Update changelog text.
> 
> Thanks.
> 
> >  - Add Kees' RB tag. 
> 
> He probably won't mind in this case, but you did some pretty substantial
> changes to the patch, so I really wouldn't recommend keeping it there.

Thanks for double-checking! Yeah, I'm fine with it; Gustavo and I had
talked in the past about similar solutions in other places, so he
forwarded the intent from those conversations. (Not that you had any
visibility into that!) But, yes, still:

Reviewed-by: Kees Cook <keescook@chromium.org>

Thanks!

-- 
Kees Cook