linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915: zero fill vma name buffer

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Message-ID: <87ee9ox0kv.fsf@intel.com>
Date:   Thu, 16 Sep 2021 13:43:28 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Tim Gardner <tim.gardner@...onical.com>,
        linux-kernel@...r.kernel.org
Cc:     Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915: zero fill vma name buffer

On Thu, 16 Sep 2021, Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com> wrote:
> On 15/09/2021 20:23, Tim Gardner wrote:
>> In capture_vma() Coverity complains of a possible buffer overrun. Even
>> though this is a static function where all call sites can be checked,
>> limiting the copy length could save some future grief.
>> 
>> CID 93300 (#1 of 1): Copy into fixed size buffer (STRING_OVERFLOW)
>> 4. fixed_size_dest: You might overrun the 16-character fixed-size string c->name
>>     by copying name without checking the length.
>> 5. parameter_as_source: Note: This defect has an elevated risk because the
>>     source argument is a parameter of the current function.
>> 1326        strcpy(c->name, name);
>> 
>> Fix any possible overflows by using strncpy(). Zero fill the name buffer to
>> guarantee ASCII string NULL termination.
>> 
>> Cc: Jani Nikula <jani.nikula@...ux.intel.com>
>> Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
>> Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>
>> Cc: David Airlie <airlied@...ux.ie>
>> Cc: Daniel Vetter <daniel@...ll.ch>
>> Cc: intel-gfx@...ts.freedesktop.org
>> Cc: dri-devel@...ts.freedesktop.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
>> ---
>>   drivers/gpu/drm/i915/i915_gpu_error.c | 7 ++++---
>>   1 file changed, 4 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
>> index 9cf6ac575de1..154df174e2d7 100644
>> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
>> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
>> @@ -1297,10 +1297,11 @@ static bool record_context(struct i915_gem_context_coredump *e,
>>   	return simulated;
>>   }
>>   
>> +#define VMA_NAME_LEN 16
>>   struct intel_engine_capture_vma {
>>   	struct intel_engine_capture_vma *next;
>>   	struct i915_vma *vma;
>> -	char name[16];
>> +	char name[VMA_NAME_LEN];
>>   };
>>   
>>   static struct intel_engine_capture_vma *
>> @@ -1314,7 +1315,7 @@ capture_vma(struct intel_engine_capture_vma *next,
>>   	if (!vma)
>>   		return next;
>>   
>> -	c = kmalloc(sizeof(*c), gfp);
>> +	c = kzalloc(sizeof(*c), gfp);
>>   	if (!c)
>>   		return next;
>>   
>> @@ -1323,7 +1324,7 @@ capture_vma(struct intel_engine_capture_vma *next,
>>   		return next;
>>   	}
>>   
>> -	strcpy(c->name, name);
>> +	strncpy(c->name, name, VMA_NAME_LEN-1);
>
> GCC is supposed to catch any problems here as you say in the commit message.
>
> But to fix I suggest a single line change to strlcpy(c->name, name, 
> sizeof(c->name)) which always null terminates as bonus.

strscpy() is preferred over both strncpy() and strlcpy(). :)

BR,
Jani.

>
> Probably same in i915_vma_coredump_create() which with strncpy would 
> have a theoretical chance of attempting to copy over a 
> non-null-terminated string.
>
> Regards,
>
> Tvrtko
>
>>   	c->vma = vma; /* reference held while active */
>>   
>>   	c->next = next;
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center