Re: [PATCH] zram: fix bug storing backing_dev

[Andrew Morton]

On Mon, 13 Aug 2018 16:38:25 +0900 Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> 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@xxxxxxxxxx>
> > Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
> > 
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
> > CC: LKML <linux-kernel@xxxxxxxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>    [4.14+]
> 
> Thanks for Cc-ing Minchan.
> 
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> 
> > > -	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.