Re: [PATCH] configfs: Remove ppos increment in configfs_write_bin_file

[Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>]

On 05/18/2016 04:16 PM, Marek Vasut wrote:
> The simple_write_to_buffer() already increments the @ppos on success,
> see fs/libfs.c simple_write_to_buffer() comment:
> 
> "
> On success, the number of bytes written is returned and the offset @ppos
> advanced by this number, or negative value is returned on error.
> "
> 
> If the configfs_write_bin_file() is invoked with @count smaller than the
> total length of the written binary file, it will be invoked multiple times.
> Since configfs_write_bin_file() increments @ppos on success, after calling
> simple_write_to_buffer(), the @ppos is incremented twice.
> 
> Subsequent invocation of configfs_write_bin_file() will result in the next
> piece of data being written to the offset twice as long as the length of
> the previous write, thus creating buffer with "holes" in it.
> 
> The simple testcase using DTO follows:
>   $ mkdir /sys/kernel/config/device-tree/overlays/1
>   $ dd bs=1 if=foo.dtbo of=/sys/kernel/config/device-tree/overlays/1/dtbo
> Without this patch, the testcase will result in twice as big buffer in the
> kernel, which is then passed to the cfs_overlay_item_dtbo_write() .
> 
> Signed-off-by: Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>
> Cc: Geert Uytterhoeven <geert+renesas-gXvu3+zWzMSzQB+pC5nmwQ@public.gmane.org>
> Cc: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
> Cc: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>

Bump, could this be applied please ?

> ---
>  fs/configfs/file.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/fs/configfs/file.c b/fs/configfs/file.c
> index 33b7ee3..bbc1252 100644
> --- a/fs/configfs/file.c
> +++ b/fs/configfs/file.c
> @@ -357,8 +357,6 @@ configfs_write_bin_file(struct file *file, const char __user *buf,
>  
>  	len = simple_write_to_buffer(buffer->bin_buffer,
>  			buffer->bin_buffer_size, ppos, buf, count);
> -	if (len > 0)
> -		*ppos += len;
>  out:
>  	mutex_unlock(&buffer->mutex);
>  	return len;
> 

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