On Tue, Mar 21, 2017 at 10:23:56AM +0800, Qu Wenruo wrote:
>
>
> At 03/21/2017 10:08 AM, Liu Bo wrote:
> > On Tue, Mar 21, 2017 at 08:44:18AM +0800, Qu Wenruo wrote:
> > >
> > >
> > > At 03/21/2017 04:23 AM, Liu Bo wrote:
> > > > On Mon, Mar 20, 2017 at 02:21:48PM +0800, Qu Wenruo wrote:
> > > > >
> > > > >
> > > > > At 03/18/2017 10:03 AM, Liu Bo wrote:
> > > > > > On Fri, Mar 17, 2017 at 01:28:45PM +0800, Qu Wenruo wrote:
> > > > > > >
> > > > > > >
> > > > > > > At 03/17/2017 12:44 PM, Liu Bo wrote:
> > > > > > > > On Fri, Feb 03, 2017 at 04:20:22PM +0800, Qu Wenruo wrote:
> > > > > > > > > Before this patch, btrfs raid56 will keep raid56 rbio even
> > > > > > > > > all its IO is
> > > > > > > > > done.
> > > > > > > > > This may save some time allocating rbio, but it can cause
> > > > > > > > > deadly
> > > > > > > > > use-after-free bug, for the following case:
> > > > > > > > >
> > > > > > > > > Original fs: 4 devices RAID5
> > > > > > > > >
> > > > > > > > > Process A | Process B
> > > > > > > > > --------------------------------------------------------------------------
> > > > > > > > > | Start device replace
> > > > > > > > > | Now the fs has 5 devices
> > > > > > > > > | devid 0: replace device
> > > > > > > > > | devid 1~4: old devices
> > > > > > > > > btrfs_map_bio() |
> > > > > > > > > |- __btrfs_map_block() |
> > > > > > > > > | bbio has 5 stripes |
> > > > > > > > > | including devid 0 |
> > > > > > > > > |- raid56_parity_write() |
> > > > > > > > > |
> > > > > > > > > raid_write_end_io() |
> > > > > > > > > |- rbio_orig_end_io() |
> > > > > > > > > |- unlock_stripe() |
> > > > > > > > > Keeps the old rbio for |
> > > > > > > > > later steal, which has |
> > > > > > > > > stripe for devid 0 |
> > > > > > > > > | Cancel device replace
> > > > > > > > > | Now the fs has 4 devices
> > > > > > > > > | devid 0 is freed
> > > > > > > > > Some IO happens |
> > > > > > > > > raid_write_end_io() |
> > > > > > > > > |- rbio_orig_end_io() |
> > > > > > > > > |- unlock_stripe() |
> > > > > > > > > |- steal_rbio() |
> > > > > > > > > Use old rbio, whose |
> > > > > > > > > bbio has freed devid 0|
> > > > > > > > > stripe |
> > > > > > > > > Any access to rbio->bbio will |
> > > > > > > > > cause general protection or NULL |
> > > > > > > > > pointer dereference |
> > > > > > > > >
> > > > > > > > > Such bug can already be triggered by fstests btrfs/069 for
> > > > > > > > > RAID5/6
> > > > > > > > > profiles.
> > > > > > > > >
> > > > > > > > > Fix it by not keeping old rbio in unlock_stripe(), so we just
> > > > > > > > > free the
> > > > > > > > > finished rbio and rbio->bbio, so above problem wont' happen.
> > > > > > > > >
> > > > > > > >
> > > > > > > > I don't think this is acceptable, keeping a cache is important
> > > > > > > > for
> > > > > > > > raid56 write performance, could you please fix it by checking
> > > > > > > > if the
> > > > > > > > device is missing?
> > > > > > >
> > > > > > > Not possible, as it's keeping the btrfs_device pointer and never
> > > > > > > release it,
> > > > > > > the stolen rbio can be kept forever until umount.
> > > > > > >
> > > > > >
> > > > > > steal_rbio() only takes pages from rbio->stripe_pages, so the cached
> > > > > > rbio->bbio is not going to the next IO's rbio because the cached one
> > > > > > got freed immediately in steal_rbio(), where could we dereference
> > > > > > rbio->bbio?
> > > > >
> > > > > Did you mean in unlock_stripe(), we still keep the rbio in cache,
> > > > > while
> > > > > release its bbio?
> > > > >
> > > >
> > > > I thought it was lock_stripe_add(), OK, so unlock_stripe() just caches
> > > > the current rbio and doens't free it. But the point about
> > > > steal_rbio() still stands, steal_rbio() is supposed to take uptodate
> > > > pages from the cached old rbio to the current processing rbio, but it
> > > > doesn't touch the cached old rbio's bbio, nor uses the cached old rbio
> > > > afterwards, instead it is the current processing rbio that would use
> > > > its bbio for writing into target devices, but it has increased its own
> > > > bio_counter.
> > > >
> > > > > This sounds quite good but I'm afraid it may cause more problems.
> > > > >
> > > > > Quite a lot of places are accessing rbio->bbio either for their btrfs
> > > > > logical address or stripes or even stripe->dev.
> > > > >
> > > >
> > > > I'm confused, could you please specify the call trace of general
> > > > protection you got in the commit log?
> > >
> > > The 4th and 5th patches are designed to fix the same problem.
> > >
> > > If one applies 5th patch only and run btrfs/069, it will cause hang when
> > > aborting replace, since btrfs_device of dev 0 is hold in bbio->stripes[]
> > > and
> > > never get released.
> > >
> > > The 4th patch is used to solve such hang.
> > >
> >
> > OK, I see.
> >
> > Firstly, the above commit log is misleading people a bit because it
> > says that steal_rbio() dereferences the device of the cached rbio and
> > that device has got free'd, but steal_rbio() actually doesn't. Yes,
> > the cached rbio holds a reference on the free'd device, but I think
> > the below 'NULL pointer dereference' comes from writing back pages
> > into target devices when doing RMW with the current rbio instead of
> > the old cached one, right?
>
> Yes, steal_bio() is not related to this problem, sorry for the confusion.
>
> >
> > Secondly, if it is the current rio that ends up this 'NULL pointer
> > dereference', it could hold a bio_counter and let the replace thread
> > canceled by scrub wait for this bio_counter to be zero. Although
> > btrfs_dev_replace_finishing() has flushed delalloc IO and committed
> > transaction, seems like scrub is an exception because it can continued
> > after committing transaction.
>
> If I understand it correctly, did you mean hold bio_counter when rbio holds
> bbio?
>
We have bio_counter to prevent the race against a successful dev
replace (such as btrfs_map_bio and btrfs_discard_extent), but for a
canceled dev replace (either it's canceled by scrub or by 'btrfs
replace cancel'), bio_counter could also be utilized to avoid the
race.
Now that scrub, which does raid parity recover, is the only one
without increasing bio_counter while accessing devices and stripes.
> That's OK, but we still need the 4th patch, or it will block replace cancel
> forever.
>
It is not the current code but patch 5 that needs patch 4 to avoid
blocking replace threads.
> >
> > Thirdly, it is possible that this canceled dev-replace could make
> > fstrim get a 'general protection' or 'NULL pointer dereference' since
> > it could access target devices and is not sychoronized by committing
> > transaction.
>
> So I'm using the refcount for btrfs_device to do full protection for it.
> As long as btrfs_dev can only be freed when no on holds it, instead of no
> bio pending for it, it should be safer.
>
If increading bio_counter could fix the bug like other use-after-free
dev-replace bugs, e.g.
4245215d6a8d Btrfs, raid56: fix use-after-free problem in the final device
replace procedure on raid56
,
I'd prefer it, a fix with keeping the benefit of caching rbio.
> >
> > Please correct me if I'm wrong since I failed to reproduce it.
>
> The bug is harder to trigger in v4.11-rc2 now.
>
> I modified btrfs/069 to make it easier to trigger, but it's still quite hard
> to reproduce it.
>
> Even with modification, the possibility is still low, at about 10~20%.
>
> Hopes the diff could help you to trigger it.
I'm using -n 2000 but no luck.
Thanks,
-liubo
>
> Thanks,
> Qu
>
> diff --git a/tests/btrfs/069 b/tests/btrfs/069
> index d939cd8..f9ff945 100755
> --- a/tests/btrfs/069
> +++ b/tests/btrfs/069
> @@ -74,7 +74,7 @@ run_test()
> _scratch_mount >>$seqres.full 2>&1
> SCRATCH_DEV_POOL=$saved_scratch_dev_pool
>
> - args=`_scale_fsstress_args -p 20 -n 100 $FSSTRESS_AVOID -d
> $SCRATCH_MNT/stressdir`
> + args=`_scale_fsstress_args -p 20 -n 1000 $FSSTRESS_AVOID -d
> $SCRATCH_MNT/stressdir`
> echo "Run fsstress $args" >>$seqres.full
> $FSSTRESS_PROG $args >/dev/null 2>&1 &
> fsstress_pid=$!
> @@ -115,9 +115,10 @@ run_test()
> }
>
> echo "Silence is golden"
> -for t in "${_btrfs_profile_configs[@]}"; do
> - run_test "$t"
> -done
> +#for t in "${_btrfs_profile_configs[@]}"; do
> +# run_test "$t"
> +#done
> +run_test "-d raid5 -m raid5"
>
> status=0
> exit
>
> >
> > Thanks,
> >
> > -liubo
> >
> > > And the kernel NULL pointer access is like this when running modified
> > > btrfs/069 (only run on RAID5, and improve the duration of fsstress):
> > >
> > > [ 884.877421] BUG: unable to handle kernel NULL pointer dereference at
> > > 00000000000005e0
> > > [ 884.878206] IP: generic_make_request_checks+0x4d/0x610
> > > [ 884.878541] PGD 2d45a067
> > > [ 884.878542] PUD 3ba0e067
> > > [ 884.878857] PMD 0
> > > [ 884.879189]
> > > [ 884.879899] Oops: 0000 [#1] SMP
> > > [ 884.880207] Modules linked in: btrfs(O) ext4 jbd2 mbcache xor raid6_pq
> > > netconsole xfs [last unloaded: btrfs]
> > > [ 884.880845] CPU: 1 PID: 11676 Comm: kworker/u4:14 Tainted: G O
> > > 4.11.0-rc2 #72
> > > [ 884.881455] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
> > > 1.10.2-20170228_101828-anatol 04/01/2014
> > > [ 884.882119] Workqueue: btrfs-endio-raid56 btrfs_endio_raid56_helper
> > > [btrfs]
> > > [ 884.883089] task: ffff88002875b4c0 task.stack: ffffc90001334000
> > > [ 884.883527] RIP: 0010:generic_make_request_checks+0x4d/0x610
> > > [ 884.883855] RSP: 0018:ffffc90001337bb8 EFLAGS: 00010283
> > > [ 884.884186] RAX: 0000000000000000 RBX: ffff8800126503e8 RCX:
> > > 0000000000218800
> > > [ 884.884539] RDX: 0000000000000040 RSI: 0000000000000001 RDI:
> > > ffff88003d8116c0
> > > [ 884.884897] RBP: ffffc90001337c18 R08: 0000000000000001 R09:
> > > 0000000000000001
> > > [ 884.885778] R10: 0000000000000000 R11: 00000000000162b9 R12:
> > > 0000000000000040
> > > [ 884.886346] R13: ffff8800126503e8 R14: 00000000ffffffff R15:
> > > 0000000000000010
> > > [ 884.887146] FS: 0000000000000000(0000) GS:ffff88003e400000(0000)
> > > knlGS:0000000000000000
> > > [ 884.888457] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > [ 884.888792] CR2: 00000000000005e0 CR3: 000000003ad30000 CR4:
> > > 00000000000006e0
> > > [ 884.889212] Call Trace:
> > > [ 884.889526] ? generic_make_request+0xc7/0x360
> > > [ 884.889841] generic_make_request+0x24/0x360
> > > [ 884.890163] ? generic_make_request+0xc7/0x360
> > > [ 884.890486] submit_bio+0x64/0x120
> > > [ 884.890828] ? page_in_rbio+0x4d/0x80 [btrfs]
> > > [ 884.891206] ? rbio_orig_end_io+0x80/0x80 [btrfs]
> > > [ 884.891543] finish_rmw+0x3f4/0x540 [btrfs]
> > > [ 884.891875] validate_rbio_for_rmw+0x36/0x40 [btrfs]
> > > [ 884.892213] raid_rmw_end_io+0x7a/0x90 [btrfs]
> > > [ 884.892565] bio_endio+0x56/0x60
> > > [ 884.892891] end_workqueue_fn+0x3c/0x40 [btrfs]
> > > [ 884.893265] btrfs_scrubparity_helper+0xef/0x620 [btrfs]
> > > [ 884.893698] btrfs_endio_raid56_helper+0xe/0x10 [btrfs]
> > > [ 884.894101] process_one_work+0x2af/0x720
> > > [ 884.894837] ? process_one_work+0x22b/0x720
> > > [ 884.895278] worker_thread+0x4b/0x4f0
> > > [ 884.895760] kthread+0x10f/0x150
> > > [ 884.896106] ? process_one_work+0x720/0x720
> > > [ 884.896448] ? kthread_create_on_node+0x40/0x40
> > > [ 884.896803] ret_from_fork+0x2e/0x40
> > > [ 884.897148] Code: 67 28 48 c7 c7 27 7f c9 81 e8 90 6c d4 ff e8 0b bb 54
> > > 00 41 c1 ec 09 48 8b 7b 08 45 85 e4 0f 85 be 00 00 00 48 8b 87 00 01 00 00
> > > <4c> 8b b0 e0 05 00 00 4d 85 f6 0f 84 86 01 00 00 4c 8b af f0 00
> > > [ 884.898449] RIP: generic_make_request_checks+0x4d/0x610 RSP:
> > > ffffc90001337bb8
> > > [ 884.899223] CR2: 00000000000005e0
> > > [ 884.900223] ---[ end trace 307e118b57a9995e ]---
> > >
> > > Thanks,
> > > Qu
> > >
> > > >
> > > > I wonder if patch 4 and 5 are fixing the same use-after-free problem?
> > > >
> > > > Thanks,
> > > >
> > > > -liubo
> > > >
> > > > > Thanks,
> > > > > Qu
> > > > >
> > > > >
> > > > > >
> > > > > > Thanks,
> > > > > >
> > > > > > -liubo
> > > > > >
> > > > > > > And I think the logical is very strange, if RAID5/6 is unstable,
> > > > > > > there is no
> > > > > > > meaning to keep it fast.
> > > > > > >
> > > > > > > Keep it stable first, and then consider the performance.
> > > > > > >
> > > > > > > Thanks,
> > > > > > > Qu
> > > > > > >
> > > > > > > >
> > > > > > > > Thanks,
> > > > > > > >
> > > > > > > > -liubo
> > > > > > > >
> > > > > > > > > Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com>
> > > > > > > > > ---
> > > > > > > > > fs/btrfs/raid56.c | 18 +-----------------
> > > > > > > > > 1 file changed, 1 insertion(+), 17 deletions(-)
> > > > > > > > >
> > > > > > > > > diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
> > > > > > > > > index 453eefdcb591..aba82b95ec73 100644
> > > > > > > > > --- a/fs/btrfs/raid56.c
> > > > > > > > > +++ b/fs/btrfs/raid56.c
> > > > > > > > > @@ -776,7 +776,6 @@ static noinline void unlock_stripe(struct
> > > > > > > > > btrfs_raid_bio *rbio)
> > > > > > > > > int bucket;
> > > > > > > > > struct btrfs_stripe_hash *h;
> > > > > > > > > unsigned long flags;
> > > > > > > > > - int keep_cache = 0;
> > > > > > > > >
> > > > > > > > > bucket = rbio_bucket(rbio);
> > > > > > > > > h = rbio->fs_info->stripe_hash_table->table + bucket;
> > > > > > > > > @@ -788,19 +787,6 @@ static noinline void
> > > > > > > > > unlock_stripe(struct btrfs_raid_bio *rbio)
> > > > > > > > > spin_lock(&rbio->bio_list_lock);
> > > > > > > > >
> > > > > > > > > if (!list_empty(&rbio->hash_list)) {
> > > > > > > > > - /*
> > > > > > > > > - * if we're still cached and there is no other
> > > > > > > > > IO
> > > > > > > > > - * to perform, just leave this rbio here for
> > > > > > > > > others
> > > > > > > > > - * to steal from later
> > > > > > > > > - */
> > > > > > > > > - if (list_empty(&rbio->plug_list) &&
> > > > > > > > > - test_bit(RBIO_CACHE_BIT, &rbio->flags)) {
> > > > > > > > > - keep_cache = 1;
> > > > > > > > > - clear_bit(RBIO_RMW_LOCKED_BIT,
> > > > > > > > > &rbio->flags);
> > > > > > > > > -
> > > > > > > > > BUG_ON(!bio_list_empty(&rbio->bio_list));
> > > > > > > > > - goto done;
> > > > > > > > > - }
> > > > > > > > > -
> > > > > > > > > list_del_init(&rbio->hash_list);
> > > > > > > > > atomic_dec(&rbio->refs);
> > > > > > > > >
> > > > > > > > > @@ -848,13 +834,11 @@ static noinline void
> > > > > > > > > unlock_stripe(struct btrfs_raid_bio *rbio)
> > > > > > > > > goto done_nolock;
> > > > > > > > > }
> > > > > > > > > }
> > > > > > > > > -done:
> > > > > > > > > spin_unlock(&rbio->bio_list_lock);
> > > > > > > > > spin_unlock_irqrestore(&h->lock, flags);
> > > > > > > > >
> > > > > > > > > done_nolock:
> > > > > > > > > - if (!keep_cache)
> > > > > > > > > - remove_rbio_from_cache(rbio);
> > > > > > > > > + remove_rbio_from_cache(rbio);
> > > > > > > > > }
> > > > > > > > >
> > > > > > > > > static void __free_raid_bio(struct btrfs_raid_bio *rbio)
> > > > > > > > > --
> > > > > > > > > 2.11.0
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
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