Re: [PATCH 1/2] drm/i915: Fix copy_to_user usage for pipe_crc

From: Daniel Vetter <daniel@ffwll.ch>
To: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 1/2] drm/i915: Fix copy_to_user usage for pipe_crc
Date: Wed, 3 Aug 2016 09:44:42 +0200	[thread overview]
Message-ID: <20160803074442.GF6232@phenom.ffwll.local> (raw)
In-Reply-To: <1470199327-5833-1-git-send-email-rodrigo.vivi@intel.com>

On Tue, Aug 02, 2016 at 09:42:06PM -0700, Rodrigo Vivi wrote:
> Copy to user return the number of bytes it couldn't write
> and zero on success. So any number different than 0 should
> be considered a fault, not only when it doesn't write
> the full size.
> 
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

I audited all the other places we use copy_*_user. We have a bit a mess
between negative errno and unwritten bytes for our own copy functions, but
seems consistent (except this one here).

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 7c42ec4..7052c47 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -3632,7 +3632,6 @@ i915_pipe_crc_read(struct file *filep, char __user *user_buf, size_t count,
>  	while (n_entries > 0) {
>  		struct intel_pipe_crc_entry *entry =
>  			&pipe_crc->entries[pipe_crc->tail];
> -		int ret;
>  
>  		if (CIRC_CNT(pipe_crc->head, pipe_crc->tail,
>  			     INTEL_PIPE_CRC_ENTRIES_NR) < 1)
> @@ -3649,8 +3648,7 @@ i915_pipe_crc_read(struct file *filep, char __user *user_buf, size_t count,
>  
>  		spin_unlock_irq(&pipe_crc->lock);
>  
> -		ret = copy_to_user(user_buf, buf, PIPE_CRC_LINE_LEN);
> -		if (ret == PIPE_CRC_LINE_LEN)
> +		if (!copy_to_user(user_buf, buf, PIPE_CRC_LINE_LEN))
>  			return -EFAULT;
>  
>  		user_buf += PIPE_CRC_LINE_LEN;
> -- 
> 2.5.5
> 
> _______________________________________________
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> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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