[Intel-gfx] [PATCH libdrm] xf86drm: Bound strstr() to the allocated data

[Ville Syrjälä]

On Fri, Jan 22, 2016 at 12:51:23PM +0000, Damien Lespiau wrote:
> We are reading at most sizeof(data) bytes, but then data may not contain
> a terminating '\0', at least in theory, so strstr() may overflow the
> stack allocated array.
> 
> Make sure that data always contains at least one '\0'.
> 
> Signed-off-by: Damien Lespiau <damien.lespiau at intel.com>
> ---
>  xf86drm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/xf86drm.c b/xf86drm.c
> index 7e28b4f..5f587d9 100644
> --- a/xf86drm.c
> +++ b/xf86drm.c
> @@ -2863,7 +2863,7 @@ static int drmParsePciBusInfo(int maj, int min, drmPciBusInfoPtr info)
>  {
>  #ifdef __linux__
>      char path[PATH_MAX + 1];
> -    char data[128];
> +    char data[128 + 1];
>      char *str;
>      int domain, bus, dev, func;
>      int fd, ret;
> @@ -2874,6 +2874,7 @@ static int drmParsePciBusInfo(int maj, int min, drmPciBusInfoPtr info)
>          return -errno;
>  
>      ret = read(fd, data, sizeof(data));
> +    data[128] = '\0';

Slightly more paranoid would be something along the lines of
if (ret >= 0)
	data[ret] = '\0';

But this should be good enough I think so
Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

The other thing I spotted while looking at the code is the fact that it
doesn't check the snprint() return value. But I guess PATH_MAX is big
enough that even if you somehow make maj and min INT_MIN it'll still
fit.

>      close(fd);
>      if (ret < 0)
>          return -errno;
> -- 
> 2.4.3
> 
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-- 
Ville Syrjälä
Intel OTC