Re: [PATCH] block: Restore tape support

[Laurence Oberman <loberman@redhat.com>]

On Mon, 2018-12-10 at 08:32 -0700, Keith Busch wrote:
> On Sun, Dec 09, 2018 at 07:08:14PM -0800, Bart Van Assche wrote:
> > According to what I found in
> > https://bugzilla.kernel.org/show_bug.cgi?id=201935 patch "block:
> > Clear
> > kernel memory before copying to user" broke tape access. Hence
> > revert
> > that patch.
> 
> Instead of reverting back to the leaking arbitrary kernel memory, why
> not just make a fix on top of it? This should do it:
> 
> ---
> diff --git a/block/bio.c b/block/bio.c
> index c4ef8aa46452..55a5386fd431 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1262,7 +1262,8 @@ struct bio *bio_copy_user_iov(struct
> request_queue *q,
>  		if (ret)
>  			goto cleanup;
>  	} else {
> -		zero_fill_bio(bio);
> +		if (bmd->is_our_pages)
> +			zero_fill_bio(bio);
>  		iov_iter_advance(iter, bio->bi_iter.bi_size);
>  	}
>  
> --
Reproduced on 4.20-rc6

# tar cvf /dev/st0 /etc
...
Showed data was written in tar
However listing is empty, data not actually written

# tar tvf /dev/st0 
#

Then:

Applied Keith Patch

# tar cvf /dev/st0 /etc
...

# tar tvf /dev/st0

Data was written and can be read

..drwxr-xr-x root/root         0 2018-10-31 08:41 etc/fwupd/
-rw-r--r-- root/root       292 2018-06-07 08:27 etc/fwupd/daemon.conf
drwxr-xr-x root/root         0 2018-10-31 08:41 etc/fwupd/remotes.d/
-rw-r--r-- root/root       181 2018-09-05 06:00
etc/fwupd/remotes.d/fwupd.conf
-rw-r--r-- root/root       327 2018-06-07 08:27
etc/fwupd/remotes.d/lvfs-testing.conf
-rw-r--r-- root/root       283 2018-09-05 06:00
etc/fwupd/remotes.d/lvfs.conf
-rw-r--r-- root/root       283 2018-09-05 06:00
etc/fwupd/remotes.d/vendor.conf
-rw-r--r-- root/root       118 2018-09-05 06:00 etc/fwupd/uefi.conf
-r--r----- root/root      4328 2018-09-25 01:57 etc/sudoers.rpmnew
-rw-r--r-- root/root      2331 2018-11-02 14:50 etc/hercules.cnf
-rw-r--r-- root/root       147 2018-11-06 17:08 etc/minirc.p2000


[   96.272548] st 2:0:0:0: [st0] Block limits 1 - 16777215 bytes.
[   96.300782] st 2:0:0:0: [st0] Mode sense. Length 11, medium 0, WBS
10, BLL 8
[   96.334985] st 2:0:0:0: [st0] Density 58, tape length: 0, drv
buffer: 1
[   96.367366] st 2:0:0:0: [st0] Block size: 0, buffer size: 4096 (1
blocks).
[   97.197209] st 2:0:0:0: [st0] Rewinding tape.
[  103.104429] st 2:0:0:0: [st0] Block limits 1 - 16777215 bytes.
[  103.133142] st 2:0:0:0: [st0] Mode sense. Length 11, medium 0, WBS
10, BLL 8
[  103.167421] st 2:0:0:0: [st0] Density 58, tape length: 0, drv
buffer: 1
[  103.199711] st 2:0:0:0: [st0] Block size: 0, buffer size: 4096 (1
blocks).
[  104.109081] st 2:0:0:0: [st0] Rewinding tape.

Tested and works fine. 
Thanks All

Tested-by: Laurence Oberman <loberman@redhat.com>