btrfs: relocation: Fix KASAN report about use-after-free due to dead reloc tree cleanup race
diff mbox series

Message ID 20190920024150.17911-1-wqu@suse.com
State New
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Series
  • btrfs: relocation: Fix KASAN report about use-after-free due to dead reloc tree cleanup race
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Commit Message

Qu WenRuo Sept. 20, 2019, 2:41 a.m. UTC
[BUG]
One user reported a reproduciable KASAN report about use-after-free:
  BTRFS info (device sdi1): balance: start -dvrange=1256811659264..1256811659265
  BTRFS info (device sdi1): relocating block group 1256811659264 flags data|raid0
  ==================================================================
  BUG: KASAN: use-after-free in btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
  Write of size 8 at addr ffff88856f671710 by task kworker/u24:10/261579

  CPU: 2 PID: 261579 Comm: kworker/u24:10 Tainted: P           OE     5.2.11-arch1-1-kasan #4
  Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./X99 Extreme4, BIOS P3.80 04/06/2018
  Workqueue: btrfs-endio-write btrfs_endio_write_helper [btrfs]
  Call Trace:
   dump_stack+0x7b/0xba
   print_address_description+0x6c/0x22e
   ? btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
   __kasan_report.cold+0x1b/0x3b
   ? btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
   kasan_report+0x12/0x17
   __asan_report_store8_noabort+0x17/0x20
   btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
   record_root_in_trans+0x2a0/0x370 [btrfs]
   btrfs_record_root_in_trans+0xf4/0x140 [btrfs]
   start_transaction+0x1ab/0xe90 [btrfs]
   btrfs_join_transaction+0x1d/0x20 [btrfs]
   btrfs_finish_ordered_io+0x7bf/0x18a0 [btrfs]
   ? lock_repin_lock+0x400/0x400
   ? __kmem_cache_shutdown.cold+0x140/0x1ad
   ? btrfs_unlink_subvol+0x9b0/0x9b0 [btrfs]
   finish_ordered_fn+0x15/0x20 [btrfs]
   normal_work_helper+0x1bd/0xca0 [btrfs]
   ? process_one_work+0x819/0x1720
   ? kasan_check_read+0x11/0x20
   btrfs_endio_write_helper+0x12/0x20 [btrfs]
   process_one_work+0x8c9/0x1720
   ? pwq_dec_nr_in_flight+0x2f0/0x2f0
   ? worker_thread+0x1d9/0x1030
   worker_thread+0x98/0x1030
   kthread+0x2bb/0x3b0
   ? process_one_work+0x1720/0x1720
   ? kthread_park+0x120/0x120
   ret_from_fork+0x35/0x40

  Allocated by task 369692:
   __kasan_kmalloc.part.0+0x44/0xc0
   __kasan_kmalloc.constprop.0+0xba/0xc0
   kasan_kmalloc+0x9/0x10
   kmem_cache_alloc_trace+0x138/0x260
   btrfs_read_tree_root+0x92/0x360 [btrfs]
   btrfs_read_fs_root+0x10/0xb0 [btrfs]
   create_reloc_root+0x47d/0xa10 [btrfs]
   btrfs_init_reloc_root+0x1e2/0x340 [btrfs]
   record_root_in_trans+0x2a0/0x370 [btrfs]
   btrfs_record_root_in_trans+0xf4/0x140 [btrfs]
   start_transaction+0x1ab/0xe90 [btrfs]
   btrfs_start_transaction+0x1e/0x20 [btrfs]
   __btrfs_prealloc_file_range+0x1c2/0xa00 [btrfs]
   btrfs_prealloc_file_range+0x13/0x20 [btrfs]
   prealloc_file_extent_cluster+0x29f/0x570 [btrfs]
   relocate_file_extent_cluster+0x193/0xc30 [btrfs]
   relocate_data_extent+0x1f8/0x490 [btrfs]
   relocate_block_group+0x600/0x1060 [btrfs]
   btrfs_relocate_block_group+0x3a0/0xa00 [btrfs]
   btrfs_relocate_chunk+0x9e/0x180 [btrfs]
   btrfs_balance+0x14e4/0x2fc0 [btrfs]
   btrfs_ioctl_balance+0x47f/0x640 [btrfs]
   btrfs_ioctl+0x119d/0x8380 [btrfs]
   do_vfs_ioctl+0x9f5/0x1060
   ksys_ioctl+0x67/0x90
   __x64_sys_ioctl+0x73/0xb0
   do_syscall_64+0xa5/0x370
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

  Freed by task 369692:
   __kasan_slab_free+0x14f/0x210
   kasan_slab_free+0xe/0x10
   kfree+0xd8/0x270
   btrfs_drop_snapshot+0x154c/0x1eb0 [btrfs]
   clean_dirty_subvols+0x227/0x340 [btrfs]
   relocate_block_group+0x972/0x1060 [btrfs]
   btrfs_relocate_block_group+0x3a0/0xa00 [btrfs]
   btrfs_relocate_chunk+0x9e/0x180 [btrfs]
   btrfs_balance+0x14e4/0x2fc0 [btrfs]
   btrfs_ioctl_balance+0x47f/0x640 [btrfs]
   btrfs_ioctl+0x119d/0x8380 [btrfs]
   do_vfs_ioctl+0x9f5/0x1060
   ksys_ioctl+0x67/0x90
   __x64_sys_ioctl+0x73/0xb0
   do_syscall_64+0xa5/0x370
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

  The buggy address belongs to the object at ffff88856f671100
   which belongs to the cache kmalloc-4k of size 4096
  The buggy address is located 1552 bytes inside of
   4096-byte region [ffff88856f671100, ffff88856f672100)
  The buggy address belongs to the page:
  page:ffffea0015bd9c00 refcount:1 mapcount:0 mapping:ffff88864400e600 index:0x0 compound_mapcount: 0
  flags: 0x2ffff0000010200(slab|head)
  raw: 02ffff0000010200 dead000000000100 dead000000000200 ffff88864400e600
  raw: 0000000000000000 0000000000070007 00000001ffffffff 0000000000000000
  page dumped because: kasan: bad access detected

  Memory state around the buggy address:
   ffff88856f671600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
   ffff88856f671680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  >ffff88856f671700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                           ^
   ffff88856f671780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
   ffff88856f671800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ==================================================================
  BTRFS info (device sdi1): 1 enospc errors during balance
  BTRFS info (device sdi1): balance: ended with status: -28

[CAUSE]
The problem happens when finish_ordered_io() get called with balance
still running, while the reloc root of that subvolume is already dead.
(tree swap already done, but tree not yet deleted for possible qgroup
usage)

That means root->reloc_root still exists, but that reloc_root can be
under btrfs_drop_snapshot(), thus we shouldn't access it.

The following race could cause the use-after-free problem:

                CPU1              |                CPU2
--------------------------------------------------------------------------
                                  | relocate_block_group()
                                  | |- unset_reloc_control(rc)
                                  | |- btrfs_commit_transaction()
btrfs_finish_ordered_io()         | |- clean_dirty_subvols()
|- btrfs_join_transaction()       |    |
   |- record_root_in_trans()      |    |
      |- btrfs_init_reloc_root()  |    |
         |- if (root->reloc_root) |    |
         |                        |    |- root->reloc_root = NULL
         |                        |    |- btrfs_drop_snapshot(reloc_root);
         |- reloc_root->last_trans|
                 = trans->transid |
	    ^^^^^^^^^^^^^^^^^^^^^^
            Use after free

It looks like the race window is pretty small so that it's not that easy
to trigger without the extra validation overhead introduced by KASAN.

[FIX]
Fix it by the following modifications:
- Test if the root has dead reloc tree before accessing root->reloc_root
  If the root has BTRFS_ROOT_DEAD_RELOC_TREE, then we don't need to
  create or update root->reloc_tree

- Clear the BTRFS_ROOT_DEAD_RELOC_TREE flag until we have fully dropped
  reloc tree
  To co-operate with above modification, so as long as
  BTRFS_ROOT_DEAD_RELOC_TREE is still set, we won't try to re-create
  reloc tree at record_root_in_trans().

Reported-by: Cebtenzzre <cebtenzzre@gmail.com>
Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/relocation.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Comments

Josef Bacik Sept. 20, 2019, 9:01 p.m. UTC | #1
On Fri, Sep 20, 2019 at 10:41:50AM +0800, Qu Wenruo wrote:
> [BUG]
> One user reported a reproduciable KASAN report about use-after-free:
>   BTRFS info (device sdi1): balance: start -dvrange=1256811659264..1256811659265
>   BTRFS info (device sdi1): relocating block group 1256811659264 flags data|raid0
>   ==================================================================
>   BUG: KASAN: use-after-free in btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
>   Write of size 8 at addr ffff88856f671710 by task kworker/u24:10/261579
> 
>   CPU: 2 PID: 261579 Comm: kworker/u24:10 Tainted: P           OE     5.2.11-arch1-1-kasan #4
>   Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./X99 Extreme4, BIOS P3.80 04/06/2018
>   Workqueue: btrfs-endio-write btrfs_endio_write_helper [btrfs]
>   Call Trace:
>    dump_stack+0x7b/0xba
>    print_address_description+0x6c/0x22e
>    ? btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
>    __kasan_report.cold+0x1b/0x3b
>    ? btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
>    kasan_report+0x12/0x17
>    __asan_report_store8_noabort+0x17/0x20
>    btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
>    record_root_in_trans+0x2a0/0x370 [btrfs]
>    btrfs_record_root_in_trans+0xf4/0x140 [btrfs]
>    start_transaction+0x1ab/0xe90 [btrfs]
>    btrfs_join_transaction+0x1d/0x20 [btrfs]
>    btrfs_finish_ordered_io+0x7bf/0x18a0 [btrfs]
>    ? lock_repin_lock+0x400/0x400
>    ? __kmem_cache_shutdown.cold+0x140/0x1ad
>    ? btrfs_unlink_subvol+0x9b0/0x9b0 [btrfs]
>    finish_ordered_fn+0x15/0x20 [btrfs]
>    normal_work_helper+0x1bd/0xca0 [btrfs]
>    ? process_one_work+0x819/0x1720
>    ? kasan_check_read+0x11/0x20
>    btrfs_endio_write_helper+0x12/0x20 [btrfs]
>    process_one_work+0x8c9/0x1720
>    ? pwq_dec_nr_in_flight+0x2f0/0x2f0
>    ? worker_thread+0x1d9/0x1030
>    worker_thread+0x98/0x1030
>    kthread+0x2bb/0x3b0
>    ? process_one_work+0x1720/0x1720
>    ? kthread_park+0x120/0x120
>    ret_from_fork+0x35/0x40
> 
>   Allocated by task 369692:
>    __kasan_kmalloc.part.0+0x44/0xc0
>    __kasan_kmalloc.constprop.0+0xba/0xc0
>    kasan_kmalloc+0x9/0x10
>    kmem_cache_alloc_trace+0x138/0x260
>    btrfs_read_tree_root+0x92/0x360 [btrfs]
>    btrfs_read_fs_root+0x10/0xb0 [btrfs]
>    create_reloc_root+0x47d/0xa10 [btrfs]
>    btrfs_init_reloc_root+0x1e2/0x340 [btrfs]
>    record_root_in_trans+0x2a0/0x370 [btrfs]
>    btrfs_record_root_in_trans+0xf4/0x140 [btrfs]
>    start_transaction+0x1ab/0xe90 [btrfs]
>    btrfs_start_transaction+0x1e/0x20 [btrfs]
>    __btrfs_prealloc_file_range+0x1c2/0xa00 [btrfs]
>    btrfs_prealloc_file_range+0x13/0x20 [btrfs]
>    prealloc_file_extent_cluster+0x29f/0x570 [btrfs]
>    relocate_file_extent_cluster+0x193/0xc30 [btrfs]
>    relocate_data_extent+0x1f8/0x490 [btrfs]
>    relocate_block_group+0x600/0x1060 [btrfs]
>    btrfs_relocate_block_group+0x3a0/0xa00 [btrfs]
>    btrfs_relocate_chunk+0x9e/0x180 [btrfs]
>    btrfs_balance+0x14e4/0x2fc0 [btrfs]
>    btrfs_ioctl_balance+0x47f/0x640 [btrfs]
>    btrfs_ioctl+0x119d/0x8380 [btrfs]
>    do_vfs_ioctl+0x9f5/0x1060
>    ksys_ioctl+0x67/0x90
>    __x64_sys_ioctl+0x73/0xb0
>    do_syscall_64+0xa5/0x370
>    entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
>   Freed by task 369692:
>    __kasan_slab_free+0x14f/0x210
>    kasan_slab_free+0xe/0x10
>    kfree+0xd8/0x270
>    btrfs_drop_snapshot+0x154c/0x1eb0 [btrfs]
>    clean_dirty_subvols+0x227/0x340 [btrfs]
>    relocate_block_group+0x972/0x1060 [btrfs]
>    btrfs_relocate_block_group+0x3a0/0xa00 [btrfs]
>    btrfs_relocate_chunk+0x9e/0x180 [btrfs]
>    btrfs_balance+0x14e4/0x2fc0 [btrfs]
>    btrfs_ioctl_balance+0x47f/0x640 [btrfs]
>    btrfs_ioctl+0x119d/0x8380 [btrfs]
>    do_vfs_ioctl+0x9f5/0x1060
>    ksys_ioctl+0x67/0x90
>    __x64_sys_ioctl+0x73/0xb0
>    do_syscall_64+0xa5/0x370
>    entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
>   The buggy address belongs to the object at ffff88856f671100
>    which belongs to the cache kmalloc-4k of size 4096
>   The buggy address is located 1552 bytes inside of
>    4096-byte region [ffff88856f671100, ffff88856f672100)
>   The buggy address belongs to the page:
>   page:ffffea0015bd9c00 refcount:1 mapcount:0 mapping:ffff88864400e600 index:0x0 compound_mapcount: 0
>   flags: 0x2ffff0000010200(slab|head)
>   raw: 02ffff0000010200 dead000000000100 dead000000000200 ffff88864400e600
>   raw: 0000000000000000 0000000000070007 00000001ffffffff 0000000000000000
>   page dumped because: kasan: bad access detected
> 
>   Memory state around the buggy address:
>    ffff88856f671600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>    ffff88856f671680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   >ffff88856f671700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                            ^
>    ffff88856f671780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>    ffff88856f671800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ==================================================================
>   BTRFS info (device sdi1): 1 enospc errors during balance
>   BTRFS info (device sdi1): balance: ended with status: -28
> 
> [CAUSE]
> The problem happens when finish_ordered_io() get called with balance
> still running, while the reloc root of that subvolume is already dead.
> (tree swap already done, but tree not yet deleted for possible qgroup
> usage)
> 
> That means root->reloc_root still exists, but that reloc_root can be
> under btrfs_drop_snapshot(), thus we shouldn't access it.
> 
> The following race could cause the use-after-free problem:
> 
>                 CPU1              |                CPU2
> --------------------------------------------------------------------------
>                                   | relocate_block_group()
>                                   | |- unset_reloc_control(rc)
>                                   | |- btrfs_commit_transaction()
> btrfs_finish_ordered_io()         | |- clean_dirty_subvols()
> |- btrfs_join_transaction()       |    |
>    |- record_root_in_trans()      |    |
>       |- btrfs_init_reloc_root()  |    |
>          |- if (root->reloc_root) |    |
>          |                        |    |- root->reloc_root = NULL
>          |                        |    |- btrfs_drop_snapshot(reloc_root);
>          |- reloc_root->last_trans|
>                  = trans->transid |
> 	    ^^^^^^^^^^^^^^^^^^^^^^
>             Use after free
> 
> It looks like the race window is pretty small so that it's not that easy
> to trigger without the extra validation overhead introduced by KASAN.
> 
> [FIX]
> Fix it by the following modifications:
> - Test if the root has dead reloc tree before accessing root->reloc_root
>   If the root has BTRFS_ROOT_DEAD_RELOC_TREE, then we don't need to
>   create or update root->reloc_tree
> 
> - Clear the BTRFS_ROOT_DEAD_RELOC_TREE flag until we have fully dropped
>   reloc tree
>   To co-operate with above modification, so as long as
>   BTRFS_ROOT_DEAD_RELOC_TREE is still set, we won't try to re-create
>   reloc tree at record_root_in_trans().
> 
> Reported-by: Cebtenzzre <cebtenzzre@gmail.com>
> Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/relocation.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index 7f219851fa23..d60993a8b2ae 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -1434,16 +1434,19 @@ int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
>  	int clear_rsv = 0;
>  	int ret;
>  
> -	if (root->reloc_root) {
> +	if (!test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state) &&
> +	    root->reloc_root) {
>  		reloc_root = root->reloc_root;
>  		reloc_root->last_trans = trans->transid;
>  		return 0;
>  	}
>  
>  	if (!rc || !rc->create_reloc_tree ||
> -	    root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
> +	    root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||
> +	    test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state))
>  		return 0;

Just move this bit above the root->reloc_root check, and drop the extra test_bit
in the above check.

>  
> +

Random newline.  The rest seems fine.  Thanks,

Josef

Patch
diff mbox series

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 7f219851fa23..d60993a8b2ae 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1434,16 +1434,19 @@  int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
 	int clear_rsv = 0;
 	int ret;
 
-	if (root->reloc_root) {
+	if (!test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state) &&
+	    root->reloc_root) {
 		reloc_root = root->reloc_root;
 		reloc_root->last_trans = trans->transid;
 		return 0;
 	}
 
 	if (!rc || !rc->create_reloc_tree ||
-	    root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
+	    root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||
+	    test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state))
 		return 0;
 
+
 	if (!trans->reloc_reserved) {
 		rsv = trans->block_rsv;
 		trans->block_rsv = rc->block_rsv;
@@ -2186,7 +2189,6 @@  static int clean_dirty_subvols(struct reloc_control *rc)
 			/* Merged subvolume, cleanup its reloc root */
 			struct btrfs_root *reloc_root = root->reloc_root;
 
-			clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
 			list_del_init(&root->reloc_dirty_list);
 			root->reloc_root = NULL;
 			if (reloc_root) {
@@ -2195,6 +2197,7 @@  static int clean_dirty_subvols(struct reloc_control *rc)
 				if (ret2 < 0 && !ret)
 					ret = ret2;
 			}
+			clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
 			btrfs_put_fs_root(root);
 		} else {
 			/* Orphan reloc tree, just clean it up */