linux-stable.git/block, branch v3.16.52 Linux kernel stable tree more bio_map_user_iov() leak fixes 2018-01-01T20:51:50+00:00 Al Viro viro@zeniv.linux.org.uk 2017-09-23T19:51:23+00:00 4b0266192d2b1701c1b316de139f200b8315e0cf commit 2b04e8f6bbb196cab4b232af0f8d48ff2c7a8058 upstream. we need to take care of failure exit as well - pages already in bio should be dropped by analogue of bio_unmap_pages(), since their refcounts had been bumped only once per reference in bio. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 2b04e8f6bbb196cab4b232af0f8d48ff2c7a8058 upstream.

we need to take care of failure exit as well - pages already
in bio should be dropped by analogue of bio_unmap_pages(),
since their refcounts had been bumped only once per reference
in bio.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
block: Relax a check in blk_start_queue() 2017-11-26T13:50:21+00:00 Bart Van Assche bart.vanassche@wdc.com 2017-08-17T20:12:44+00:00 873ae9976c056a962c2ce4678b93b84bf7c7f25f commit 4ddd56b003f251091a67c15ae3fe4a5c5c5e390a upstream. Calling blk_start_queue() from interrupt context with the queue lock held and without disabling IRQs, as the skd driver does, is safe. This patch avoids that loading the skd driver triggers the following warning: WARNING: CPU: 11 PID: 1348 at block/blk-core.c:283 blk_start_queue+0x84/0xa0 RIP: 0010:blk_start_queue+0x84/0xa0 Call Trace: skd_unquiesce_dev+0x12a/0x1d0 [skd] skd_complete_internal+0x1e7/0x5a0 [skd] skd_complete_other+0xc2/0xd0 [skd] skd_isr_completion_posted.isra.30+0x2a5/0x470 [skd] skd_isr+0x14f/0x180 [skd] irq_forced_thread_fn+0x2a/0x70 irq_thread+0x144/0x1a0 kthread+0x125/0x140 ret_from_fork+0x2a/0x40 Fixes: commit a038e2536472 ("[PATCH] blk_start_queue() must be called with irq disabled - add warning") Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com> Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Cc: Andrew Morton <akpm@osdl.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Hannes Reinecke <hare@suse.de> Cc: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by: Jens Axboe <axboe@kernel.dk> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 4ddd56b003f251091a67c15ae3fe4a5c5c5e390a upstream.

Calling blk_start_queue() from interrupt context with the queue
lock held and without disabling IRQs, as the skd driver does, is
safe. This patch avoids that loading the skd driver triggers the
following warning:

WARNING: CPU: 11 PID: 1348 at block/blk-core.c:283 blk_start_queue+0x84/0xa0
RIP: 0010:blk_start_queue+0x84/0xa0
Call Trace:
 skd_unquiesce_dev+0x12a/0x1d0 [skd]
 skd_complete_internal+0x1e7/0x5a0 [skd]
 skd_complete_other+0xc2/0xd0 [skd]
 skd_isr_completion_posted.isra.30+0x2a5/0x470 [skd]
 skd_isr+0x14f/0x180 [skd]
 irq_forced_thread_fn+0x2a/0x70
 irq_thread+0x144/0x1a0
 kthread+0x125/0x140
 ret_from_fork+0x2a/0x40

Fixes: commit a038e2536472 ("[PATCH] blk_start_queue() must be called with irq disabled - add warning")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
fix unbalanced page refcounting in bio_map_user_iov 2017-11-11T13:33:37+00:00 Vitaly Mayatskikh v.mayatskih@gmail.com 2017-09-22T05:18:39+00:00 3c885aa3b459aabc5fa04251a5fdd88e29b1de70 commit 95d78c28b5a85bacbc29b8dba7c04babb9b0d467 upstream. bio_map_user_iov and bio_unmap_user do unbalanced pages refcounting if IO vector has small consecutive buffers belonging to the same page. bio_add_pc_page merges them into one, but the page reference is never dropped. Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 95d78c28b5a85bacbc29b8dba7c04babb9b0d467 upstream.

bio_map_user_iov and bio_unmap_user do unbalanced pages refcounting if
IO vector has small consecutive buffers belonging to the same page.
bio_add_pc_page merges them into one, but the page reference is never
dropped.

Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
block: fix an error code in add_partition() 2017-09-15T17:29:49+00:00 Dan Carpenter dan.carpenter@oracle.com 2017-05-23T14:28:36+00:00 d74706c22cfe345dc1e47473855bee2d713b45d5 commit 7bd897cfce1eb373892d35d7f73201b0f9b221c4 upstream. We don't set an error code on this path. It means that we return NULL instead of an error pointer and the caller does a NULL dereference. Fixes: 6d1d8050b4bc ("block, partition: add partition_meta_info to hd_struct") Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 7bd897cfce1eb373892d35d7f73201b0f9b221c4 upstream.

We don't set an error code on this path.  It means that we return NULL
instead of an error pointer and the caller does a NULL dereference.

Fixes: 6d1d8050b4bc ("block, partition: add partition_meta_info to hd_struct")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
sbitmap: fix wakeup hang after sbq resize 2017-06-05T20:16:55+00:00 Omar Sandoval osandov@fb.com 2017-01-18T19:55:22+00:00 85edb87c082d9e0f42d874610c68e7c3003c9870 commit 6c0ca7ae292adea09b8bdd33a524bb9326c3e989 upstream. When we resize a struct sbitmap_queue, we update the wakeup batch size, but we don't update the wait count in the struct sbq_wait_states. If we resized down from a size which could use a bigger batch size, these counts could be too large and cause us to miss necessary wakeups. To fix this, update the wait counts when we resize (ensuring some careful memory ordering so that it's safe w.r.t. concurrent clears). This also fixes a theoretical issue where two threads could end up bumping the wait count up by the batch size, which could also potentially lead to hangs. Reported-by: Martin Raiber <martin@urbackup.org> Fixes: e3a2b3f931f5 ("blk-mq: allow changing of queue depth through sysfs") Fixes: 2971c35f3588 ("blk-mq: bitmap tag: fix race on blk_mq_bitmap_tags::wake_cnt") Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com> [bwh: Backported to 3.16: - Adjust filename - Rename almost everything - Use ACCESS_ONCE() instead of {READ,WRITE}_ONCE()] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 6c0ca7ae292adea09b8bdd33a524bb9326c3e989 upstream.

When we resize a struct sbitmap_queue, we update the wakeup batch size,
but we don't update the wait count in the struct sbq_wait_states. If we
resized down from a size which could use a bigger batch size, these
counts could be too large and cause us to miss necessary wakeups. To fix
this, update the wait counts when we resize (ensuring some careful
memory ordering so that it's safe w.r.t. concurrent clears).

This also fixes a theoretical issue where two threads could end up
bumping the wait count up by the batch size, which could also
potentially lead to hangs.

Reported-by: Martin Raiber <martin@urbackup.org>
Fixes: e3a2b3f931f5 ("blk-mq: allow changing of queue depth through sysfs")
Fixes: 2971c35f3588 ("blk-mq: bitmap tag: fix race on blk_mq_bitmap_tags::wake_cnt")
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
[bwh: Backported to 3.16:
 - Adjust filename
 - Rename almost everything
 - Use ACCESS_ONCE() instead of {READ,WRITE}_ONCE()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
blk-mq: Make bt_clear_tag() easier to read 2017-06-05T20:16:55+00:00 Bart Van Assche bvanassche@acm.org 2014-10-07T14:45:21+00:00 eb7175dd1c6f0713d4312e745103354bb0abaed5 commit 9d8f0bcca6ffa024a822ce4ab1008ab663f06672 upstream. Eliminate a backwards goto statement from bt_clear_tag(). Signed-off-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 9d8f0bcca6ffa024a822ce4ab1008ab663f06672 upstream.

Eliminate a backwards goto statement from bt_clear_tag().

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
sg_write()/bsg_write() is not fit to be called under KERNEL_DS 2017-02-23T03:54:47+00:00 Al Viro viro@zeniv.linux.org.uk 2016-12-16T18:42:06+00:00 249741c2c0d7a905da66efc6d1292d3915aef1fc commit 128394eff343fc6d2f32172f03e24829539c5835 upstream. Both damn things interpret userland pointers embedded into the payload; worse, they are actually traversing those. Leaving aside the bad API design, this is very much _not_ safe to call with KERNEL_DS. Bail out early if that happens. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 128394eff343fc6d2f32172f03e24829539c5835 upstream.

Both damn things interpret userland pointers embedded into the payload;
worse, they are actually traversing those.  Leaving aside the bad
API design, this is very much _not_ safe to call with KERNEL_DS.
Bail out early if that happens.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
blkcg: Annotate blkg_hint correctly 2017-02-23T03:54:03+00:00 Bart Van Assche bart.vanassche@sandisk.com 2016-09-23T16:07:56+00:00 ea1c052896d88cbc8fd777998cc6ae7c8865f0d2 commit 55679c8d23d191c24ad133abc5647e3054ca8de1 upstream. Avoid that sparse complains about blkg_hint manipulations. Fixes: a637120e4902 ("blkcg: use radix tree to index blkgs from blkcg") Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@fb.com> [bwh: Backported to 3.16: adjust filename] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 55679c8d23d191c24ad133abc5647e3054ca8de1 upstream.

Avoid that sparse complains about blkg_hint manipulations.

Fixes: a637120e4902 ("blkcg: use radix tree to index blkgs from blkcg")
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
block: fix bdi vs gendisk lifetime mismatch 2016-11-20T01:17:05+00:00 Dan Williams dan.j.williams@intel.com 2016-07-31T18:15:13+00:00 dae435005a0a398dde9a421e222c379bbad0c643 commit df08c32ce3be5be138c1dbfcba203314a3a7cd6f upstream. The name for a bdi of a gendisk is derived from the gendisk's devt. However, since the gendisk is destroyed before the bdi it leaves a window where a new gendisk could dynamically reuse the same devt while a bdi with the same name is still live. Arrange for the bdi to hold a reference against its "owner" disk device while it is registered. Otherwise we can hit sysfs duplicate name collisions like the following: WARNING: CPU: 10 PID: 2078 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x64/0x80 sysfs: cannot create duplicate filename '/devices/virtual/bdi/259:1' Hardware name: HP ProLiant DL580 Gen8, BIOS P79 05/06/2015 0000000000000286 0000000002c04ad5 ffff88006f24f970 ffffffff8134caec ffff88006f24f9c0 0000000000000000 ffff88006f24f9b0 ffffffff8108c351 0000001f0000000c ffff88105d236000 ffff88105d1031e0 ffff8800357427f8 Call Trace: [<ffffffff8134caec>] dump_stack+0x63/0x87 [<ffffffff8108c351>] __warn+0xd1/0xf0 [<ffffffff8108c3cf>] warn_slowpath_fmt+0x5f/0x80 [<ffffffff812a0d34>] sysfs_warn_dup+0x64/0x80 [<ffffffff812a0e1e>] sysfs_create_dir_ns+0x7e/0x90 [<ffffffff8134faaa>] kobject_add_internal+0xaa/0x320 [<ffffffff81358d4e>] ? vsnprintf+0x34e/0x4d0 [<ffffffff8134ff55>] kobject_add+0x75/0xd0 [<ffffffff816e66b2>] ? mutex_lock+0x12/0x2f [<ffffffff8148b0a5>] device_add+0x125/0x610 [<ffffffff8148b788>] device_create_groups_vargs+0xd8/0x100 [<ffffffff8148b7cc>] device_create_vargs+0x1c/0x20 [<ffffffff811b775c>] bdi_register+0x8c/0x180 [<ffffffff811b7877>] bdi_register_dev+0x27/0x30 [<ffffffff813317f5>] add_disk+0x175/0x4a0 Reported-by: Yi Zhang <yizhan@redhat.com> Tested-by: Yi Zhang <yizhan@redhat.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Fixed up missing 0 return in bdi_register_owner(). Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit df08c32ce3be5be138c1dbfcba203314a3a7cd6f upstream.

The name for a bdi of a gendisk is derived from the gendisk's devt.
However, since the gendisk is destroyed before the bdi it leaves a
window where a new gendisk could dynamically reuse the same devt while a
bdi with the same name is still live.  Arrange for the bdi to hold a
reference against its "owner" disk device while it is registered.
Otherwise we can hit sysfs duplicate name collisions like the following:

 WARNING: CPU: 10 PID: 2078 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x64/0x80
 sysfs: cannot create duplicate filename '/devices/virtual/bdi/259:1'

 Hardware name: HP ProLiant DL580 Gen8, BIOS P79 05/06/2015
  0000000000000286 0000000002c04ad5 ffff88006f24f970 ffffffff8134caec
  ffff88006f24f9c0 0000000000000000 ffff88006f24f9b0 ffffffff8108c351
  0000001f0000000c ffff88105d236000 ffff88105d1031e0 ffff8800357427f8
 Call Trace:
  [<ffffffff8134caec>] dump_stack+0x63/0x87
  [<ffffffff8108c351>] __warn+0xd1/0xf0
  [<ffffffff8108c3cf>] warn_slowpath_fmt+0x5f/0x80
  [<ffffffff812a0d34>] sysfs_warn_dup+0x64/0x80
  [<ffffffff812a0e1e>] sysfs_create_dir_ns+0x7e/0x90
  [<ffffffff8134faaa>] kobject_add_internal+0xaa/0x320
  [<ffffffff81358d4e>] ? vsnprintf+0x34e/0x4d0
  [<ffffffff8134ff55>] kobject_add+0x75/0xd0
  [<ffffffff816e66b2>] ? mutex_lock+0x12/0x2f
  [<ffffffff8148b0a5>] device_add+0x125/0x610
  [<ffffffff8148b788>] device_create_groups_vargs+0xd8/0x100
  [<ffffffff8148b7cc>] device_create_vargs+0x1c/0x20
  [<ffffffff811b775c>] bdi_register+0x8c/0x180
  [<ffffffff811b7877>] bdi_register_dev+0x27/0x30
  [<ffffffff813317f5>] add_disk+0x175/0x4a0

Reported-by: Yi Zhang <yizhan@redhat.com>
Tested-by: Yi Zhang <yizhan@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Fixed up missing 0 return in bdi_register_owner().

Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
block: fix use-after-free in seq file 2016-11-20T01:17:04+00:00 Vegard Nossum vegard.nossum@oracle.com 2016-07-29T08:40:31+00:00 2dabc3a663edfc35c2ab48f4d6b51114757b858c commit 77da160530dd1dc94f6ae15a981f24e5f0021e84 upstream. I got a KASAN report of use-after-free: ================================================================== BUG: KASAN: use-after-free in klist_iter_exit+0x61/0x70 at addr ffff8800b6581508 Read of size 8 by task trinity-c1/315 ============================================================================= BUG kmalloc-32 (Not tainted): kasan: bad access detected ----------------------------------------------------------------------------- Disabling lock debugging due to kernel taint INFO: Allocated in disk_seqf_start+0x66/0x110 age=144 cpu=1 pid=315 ___slab_alloc+0x4f1/0x520 __slab_alloc.isra.58+0x56/0x80 kmem_cache_alloc_trace+0x260/0x2a0 disk_seqf_start+0x66/0x110 traverse+0x176/0x860 seq_read+0x7e3/0x11a0 proc_reg_read+0xbc/0x180 do_loop_readv_writev+0x134/0x210 do_readv_writev+0x565/0x660 vfs_readv+0x67/0xa0 do_preadv+0x126/0x170 SyS_preadv+0xc/0x10 do_syscall_64+0x1a1/0x460 return_from_SYSCALL_64+0x0/0x6a INFO: Freed in disk_seqf_stop+0x42/0x50 age=160 cpu=1 pid=315 __slab_free+0x17a/0x2c0 kfree+0x20a/0x220 disk_seqf_stop+0x42/0x50 traverse+0x3b5/0x860 seq_read+0x7e3/0x11a0 proc_reg_read+0xbc/0x180 do_loop_readv_writev+0x134/0x210 do_readv_writev+0x565/0x660 vfs_readv+0x67/0xa0 do_preadv+0x126/0x170 SyS_preadv+0xc/0x10 do_syscall_64+0x1a1/0x460 return_from_SYSCALL_64+0x0/0x6a CPU: 1 PID: 315 Comm: trinity-c1 Tainted: G B 4.7.0+ #62 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 ffffea0002d96000 ffff880119b9f918 ffffffff81d6ce81 ffff88011a804480 ffff8800b6581500 ffff880119b9f948 ffffffff8146c7bd ffff88011a804480 ffffea0002d96000 ffff8800b6581500 fffffffffffffff4 ffff880119b9f970 Call Trace: [<ffffffff81d6ce81>] dump_stack+0x65/0x84 [<ffffffff8146c7bd>] print_trailer+0x10d/0x1a0 [<ffffffff814704ff>] object_err+0x2f/0x40 [<ffffffff814754d1>] kasan_report_error+0x221/0x520 [<ffffffff8147590e>] __asan_report_load8_noabort+0x3e/0x40 [<ffffffff83888161>] klist_iter_exit+0x61/0x70 [<ffffffff82404389>] class_dev_iter_exit+0x9/0x10 [<ffffffff81d2e8ea>] disk_seqf_stop+0x3a/0x50 [<ffffffff8151f812>] seq_read+0x4b2/0x11a0 [<ffffffff815f8fdc>] proc_reg_read+0xbc/0x180 [<ffffffff814b24e4>] do_loop_readv_writev+0x134/0x210 [<ffffffff814b4c45>] do_readv_writev+0x565/0x660 [<ffffffff814b8a17>] vfs_readv+0x67/0xa0 [<ffffffff814b8de6>] do_preadv+0x126/0x170 [<ffffffff814b92ec>] SyS_preadv+0xc/0x10 This problem can occur in the following situation: open() - pread() - .seq_start() - iter = kmalloc() // succeeds - seqf->private = iter - .seq_stop() - kfree(seqf->private) - pread() - .seq_start() - iter = kmalloc() // fails - .seq_stop() - class_dev_iter_exit(seqf->private) // boom! old pointer As the comment in disk_seqf_stop() says, stop is called even if start failed, so we need to reinitialise the private pointer to NULL when seq iteration stops. An alternative would be to set the private pointer to NULL when the kmalloc() in disk_seqf_start() fails. Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 77da160530dd1dc94f6ae15a981f24e5f0021e84 upstream.

I got a KASAN report of use-after-free:

    ==================================================================
    BUG: KASAN: use-after-free in klist_iter_exit+0x61/0x70 at addr ffff8800b6581508
    Read of size 8 by task trinity-c1/315
    =============================================================================
    BUG kmalloc-32 (Not tainted): kasan: bad access detected
    -----------------------------------------------------------------------------

    Disabling lock debugging due to kernel taint
    INFO: Allocated in disk_seqf_start+0x66/0x110 age=144 cpu=1 pid=315
            ___slab_alloc+0x4f1/0x520
            __slab_alloc.isra.58+0x56/0x80
            kmem_cache_alloc_trace+0x260/0x2a0
            disk_seqf_start+0x66/0x110
            traverse+0x176/0x860
            seq_read+0x7e3/0x11a0
            proc_reg_read+0xbc/0x180
            do_loop_readv_writev+0x134/0x210
            do_readv_writev+0x565/0x660
            vfs_readv+0x67/0xa0
            do_preadv+0x126/0x170
            SyS_preadv+0xc/0x10
            do_syscall_64+0x1a1/0x460
            return_from_SYSCALL_64+0x0/0x6a
    INFO: Freed in disk_seqf_stop+0x42/0x50 age=160 cpu=1 pid=315
            __slab_free+0x17a/0x2c0
            kfree+0x20a/0x220
            disk_seqf_stop+0x42/0x50
            traverse+0x3b5/0x860
            seq_read+0x7e3/0x11a0
            proc_reg_read+0xbc/0x180
            do_loop_readv_writev+0x134/0x210
            do_readv_writev+0x565/0x660
            vfs_readv+0x67/0xa0
            do_preadv+0x126/0x170
            SyS_preadv+0xc/0x10
            do_syscall_64+0x1a1/0x460
            return_from_SYSCALL_64+0x0/0x6a

    CPU: 1 PID: 315 Comm: trinity-c1 Tainted: G    B           4.7.0+ #62
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
     ffffea0002d96000 ffff880119b9f918 ffffffff81d6ce81 ffff88011a804480
     ffff8800b6581500 ffff880119b9f948 ffffffff8146c7bd ffff88011a804480
     ffffea0002d96000 ffff8800b6581500 fffffffffffffff4 ffff880119b9f970
    Call Trace:
     [<ffffffff81d6ce81>] dump_stack+0x65/0x84
     [<ffffffff8146c7bd>] print_trailer+0x10d/0x1a0
     [<ffffffff814704ff>] object_err+0x2f/0x40
     [<ffffffff814754d1>] kasan_report_error+0x221/0x520
     [<ffffffff8147590e>] __asan_report_load8_noabort+0x3e/0x40
     [<ffffffff83888161>] klist_iter_exit+0x61/0x70
     [<ffffffff82404389>] class_dev_iter_exit+0x9/0x10
     [<ffffffff81d2e8ea>] disk_seqf_stop+0x3a/0x50
     [<ffffffff8151f812>] seq_read+0x4b2/0x11a0
     [<ffffffff815f8fdc>] proc_reg_read+0xbc/0x180
     [<ffffffff814b24e4>] do_loop_readv_writev+0x134/0x210
     [<ffffffff814b4c45>] do_readv_writev+0x565/0x660
     [<ffffffff814b8a17>] vfs_readv+0x67/0xa0
     [<ffffffff814b8de6>] do_preadv+0x126/0x170
     [<ffffffff814b92ec>] SyS_preadv+0xc/0x10

This problem can occur in the following situation:

open()
 - pread()
    - .seq_start()
       - iter = kmalloc() // succeeds
       - seqf->private = iter
    - .seq_stop()
       - kfree(seqf->private)
 - pread()
    - .seq_start()
       - iter = kmalloc() // fails
    - .seq_stop()
       - class_dev_iter_exit(seqf->private) // boom! old pointer

As the comment in disk_seqf_stop() says, stop is called even if start
failed, so we need to reinitialise the private pointer to NULL when seq
iteration stops.

An alternative would be to set the private pointer to NULL when the
kmalloc() in disk_seqf_start() fails.

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>