linux-kernel - Re: [PATCH] zram: fix bug storing backing

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Date:   Tue, 14 Aug 2018 16:45:23 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        Peter Kalauskas <peskal@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] zram: fix bug storing backing_dev

On Mon, 13 Aug 2018 16:38:25 +0900 Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote:

> On (08/13/18 15:16), Minchan Kim wrote:
> > > The call to strlcpy in backing_dev_store is incorrect. It should take
> > > the size of the destination buffer instead of the size of the source
> > > buffer.  Additionally, ignore the newline character (\n) when reading
> > > the new file_name buffer. This makes it possible to set the backing_dev
> > > as follows:
> > > 
> > >   echo /dev/sdX > /sys/block/zram0/backing_dev
> > > 
> > > Signed-off-by: Peter Kalauskas <peskal@...gle.com>
> > Acked-by: Minchan Kim <minchan@...nel.org>
> > 
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
> > CC: LKML <linux-kernel@...r.kernel.org>
> > Cc: <stable@...r.kernel.org>    [4.14+]
> 
> Thanks for Cc-ing Minchan.
> 
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> 
> > > -	strlcpy(file_name, buf, len);
> 
> This is quite interesting. The reason it worked before was the fact that
> strlcpy() copies 'len - 1' bytes, which is strlen(buf) - 1 in our case,
> so it accidentally didn't copy the trailing new line symbol. Which also
> means that "echo -n /dev/sdX" most likely was broken.
> 

I can't find the original email on lkml for some reason, but I
recreated the patch.

The changelog doesn't describe the end-user impact of the bug, which is
very desirable when tagging a patch for -stable backporting.  Can we
have that paragraph please?

The implementation might be able to use strim() somehow.