Re: [PATCH] Btrfs: fix divide error upon chunk's stripe_len

[Liu Bo <bo.li.liu@oracle.com>]

On Fri, Apr 29, 2016 at 11:20:31AM +0800, Qu Wenruo wrote:
> 
> 
> Liu Bo wrote on 2016/04/28 10:48 -0700:
> >On Wed, Apr 27, 2016 at 07:33:18PM +0200, David Sterba wrote:
> >>On Wed, Apr 27, 2016 at 10:23:35AM -0700, Liu Bo wrote:
> >>>On Wed, Apr 27, 2016 at 06:39:03PM +0200, David Sterba wrote:
> >>>>On Tue, Apr 26, 2016 at 05:53:31PM -0700, Liu Bo wrote:
> >>>>>The struct 'map_lookup' uses type int for @stripe_len, while
> >>>>>btrfs_chunk_stripe_len() can return a u64 value, and it may end up with
> >>>>>@stripe_len being undefined value and it can lead to 'divide error' in
> >>>>> __btrfs_map_block().
> >>>>>
> >>>>>This changes 'map_lookup' to use type u64 for stripe_len, also right now
> >>>>>we only use BTRFS_STRIPE_LEN for stripe_len, so this adds a valid checker for
> >>>>>BTRFS_STRIPE_LEN.
> >>>>>
> >>>>>Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
> >>>>>Reported-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
> >>>>
> >>>>I smell some fuzzing :) do you have the image available? I'll add it to
> >>>>the rest in btrfsprogs.
> >>>
> >>>Sure, it's on the way, I'll send it along with a patch for btrfsck (we
> >>>have to add the same validation check for superblock and chunk in
> >>>btrfsck.)
> >>
> >>Great!
> >>
> >>>>>Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> >>>>>---
> >>>>> fs/btrfs/volumes.c | 2 +-
> >>>>> fs/btrfs/volumes.h | 2 +-
> >>>>> 2 files changed, 2 insertions(+), 2 deletions(-)
> >>>>>
> >>>>>diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> >>>>>index e2b54d5..b5cb859 100644
> >>>>>--- a/fs/btrfs/volumes.c
> >>>>>+++ b/fs/btrfs/volumes.c
> >>>>>@@ -6242,7 +6242,7 @@ static int read_one_chunk(struct btrfs_root *root, struct btrfs_key *key,
> >>>>> 			"invalid chunk length %llu", length);
> >>>>> 		return -EIO;
> >>>>> 	}
> >>>>>-	if (!is_power_of_2(stripe_len)) {
> >>>>>+	if (!is_power_of_2(stripe_len) || stripe_len != BTRFS_STRIPE_LEN) {
> >
> >We don't need the first 'is_power_of_2' check.
> >
> >And I think we may need to have another helper, such as btrfs_check_chunk_valid(),
> >to cover all these (both current and future) validation checks.  What do you think?
> >
> >Thanks,
> >
> >-liubo
> >
> 
> +1 for a btrfs_check_chunk_valid().
> 
> And I'm OK to remove is_power_of_2 check, as it's only used for future
> stripe_len.
> But we only support fix STRIPE_LEN, it's OK to remove it.

OK.

> 
> BTW, did it crash btrfs-progs?

Yes, not really crash progs, but btrfsck doesn't detect errors.

I've made a patch and I'm testing it to make sure everything works.

Thanks,

-liubo

> 
> Thanks,
> Qu
> 
> >>>>
> >>>>Unfortunatelly this will break current state, as mkfs does not set the
> >>>>stripe length to 64k but to 4k. But the value is otherwise ignored in
> >>>>kernel.
> >>>
> >>>This is chunk's stripe_len, not superblock's stripe_len:
> >>>
> >>>make_btrfs() {
> >>>	...
> >>>	btrfs_set_super_stripesize(&super, cfg->stripesize); --> 4096
> >>>	...
> >>>	btrfs_set_chunk_stripe_len(buf, chunk, 64 * 1024);
> >>>}
> >>
> >>Oh right, and the hardcoded stripe chunk size would need to be fixed in
> >>a lot more places so it's fine. Consider this
> >>
> >>Reviewed-by: David Sterba <dsterba@suse.com>
> >>
> >>and on the way to for-next.
> >--
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> >
> >
> 
>