[PATCH v4 3/3] btrfs: fix use-after-free on quota enable allocation failure

[Qu Wenruo <wqu@suse.com>]

From: Yalagada Pavan Kumar <pavankumaryalagada@gmail.com>

[BUG]
There is a syzbot report that a use-after-free bug is triggered after a
failed btrfs_quota_enable():

 loop0: detected capacity change from 32768 to 0
 ==================================================================
 BUG: KASAN: slab-use-after-free in __list_add_valid_or_report+0x4e/0x130 lib/list_debug.c:29
 Read of size 8 at addr ffff888040e0a528 by task syz.0.0/5324

 CPU: 0 UID: 0 PID: 5324 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
 Call Trace:
  <TASK>
  dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
  print_address_description+0x55/0x1e0 mm/kasan/report.c:378
  print_report+0x58/0x70 mm/kasan/report.c:482
  kasan_report+0x117/0x150 mm/kasan/report.c:595
  __list_add_valid_or_report+0x4e/0x130 lib/list_debug.c:29
  __list_add_valid include/linux/list.h:104 [inline]
  __list_add include/linux/list.h:169 [inline]
  list_add include/linux/list.h:192 [inline]
  list_move include/linux/list.h:345 [inline]
  add_root_to_dirty_list+0x38b/0x470 fs/btrfs/ctree.c:232
  btrfs_force_cow_block+0xf09/0x1bf0 fs/btrfs/ctree.c:553
  btrfs_cow_block+0x3f1/0xaf0 fs/btrfs/ctree.c:696
  btrfs_search_slot+0xd70/0x2d20 fs/btrfs/ctree.c:-1
  btrfs_search_prev_slot fs/btrfs/free-space-tree.c:134 [inline]
  remove_free_space_extent fs/btrfs/free-space-tree.c:732 [inline]
  __btrfs_remove_from_free_space_tree fs/btrfs/free-space-tree.c:837 [inline]
  btrfs_remove_from_free_space_tree+0x4d6/0xda0 fs/btrfs/free-space-tree.c:866
  alloc_reserved_extent+0x4a/0x2b0 fs/btrfs/extent-tree.c:4976
  alloc_reserved_tree_block fs/btrfs/extent-tree.c:5155 [inline]
  run_delayed_tree_ref fs/btrfs/extent-tree.c:1815 [inline]
  run_one_delayed_ref fs/btrfs/extent-tree.c:1851 [inline]
  btrfs_run_delayed_refs_for_head fs/btrfs/extent-tree.c:2058 [inline]
  __btrfs_run_delayed_refs+0x18b5/0x43b0 fs/btrfs/extent-tree.c:2134
  btrfs_run_delayed_refs+0xdc/0x2a0 fs/btrfs/extent-tree.c:2246
  btrfs_commit_transaction+0x28a/0x3170 fs/btrfs/transaction.c:2267
  sync_filesystem+0x1d2/0x240 fs/sync.c:66
  btrfs_reconfigure+0x2dc/0x2100 fs/btrfs/super.c:1511
  reconfigure_super+0x232/0x8f0 fs/super.c:1128
  do_remount fs/namespace.c:3410 [inline]
  path_mount+0xd4e/0x1050 fs/namespace.c:4160
  do_mount fs/namespace.c:4181 [inline]
  __do_sys_mount fs/namespace.c:4397 [inline]
  __se_sys_mount+0x31d/0x420 fs/namespace.c:4374
  do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
  do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
  entry_SYSCALL_64_after_hwframe+0x77/0x7f
 RIP: 0033:0x7f9c8dd9f3ca
  </TASK>

 Allocated by task 5323:
  kasan_save_stack mm/kasan/common.c:57 [inline]
  kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
  poison_kmalloc_redzone mm/kasan/common.c:409 [inline]
  __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:426
  kasan_kmalloc include/linux/kasan.h:263 [inline]
  __kmalloc_cache_noprof+0x321/0x600 mm/slub.c:5563
  _kmalloc_noprof include/linux/slab.h:991 [inline]
  _kzalloc_noprof include/linux/slab.h:1312 [inline]
  btrfs_alloc_root+0x75/0x840 fs/btrfs/disk-io.c:638
  btrfs_create_tree+0xa8/0x5c0 fs/btrfs/disk-io.c:832
  btrfs_quota_enable+0x3d6/0x1e20 fs/btrfs/qgroup.c:1074
  btrfs_ioctl_quota_ctl+0x186/0x1f0 fs/btrfs/ioctl.c:3581
  vfs_ioctl fs/ioctl.c:51 [inline]
  __do_sys_ioctl fs/ioctl.c:597 [inline]
  __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
  do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
  do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
  entry_SYSCALL_64_after_hwframe+0x77/0x7f

 Freed by task 5323:
  kasan_save_stack mm/kasan/common.c:57 [inline]
  kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
  kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584
  poison_slab_object mm/kasan/common.c:264 [inline]
  __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:296
  kasan_slab_free include/linux/kasan.h:235 [inline]
  slab_free_hook mm/slub.c:2748 [inline]
  slab_free mm/slub.c:6508 [inline]
  kfree+0x1c5/0x650 mm/slub.c:6801
  btrfs_quota_enable+0x1208/0x1e20 fs/btrfs/qgroup.c:1292
  btrfs_ioctl_quota_ctl+0x186/0x1f0 fs/btrfs/ioctl.c:3581
  vfs_ioctl fs/ioctl.c:51 [inline]
  __do_sys_ioctl fs/ioctl.c:597 [inline]
  __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
  do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
  do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
  entry_SYSCALL_64_after_hwframe+0x77/0x7f

[CAUSE]
During btrfs_quota_enable(), a temporary quota_root is created, then
qgroup items are created for each subvolume and inserted into that root.

If there are enough subvolumes, the level of quota_root will be bumped,
and add_root_to_dirty_list() will be called, adding
quota_root->dirty_list into fs_info->dirty_cowonly_roots.

But if a problem is hit during btrfs_quota_enable() later, that
quota_root will be released through btrfs_put_root(), causing the whole
quota_root structure to be released, while leaving
fs_info->dirty_cowonly_roots still pointing to the released
quota_root->dirty_list.

Later access through fs_info->dirty_cowonly_roots will trigger a
use-after-free bug.

[FIX]
With previous patches doing the preparation work:

- Always hold the trans_lock when modifying btrfs_root::dirty_list
- Unlink all btrfs_root::dirty_list entries from
  btrfs_transaction::switch_commits when a transaction is cleaned up

Now we can just call list_del_init(&root->dirty_list) when
btrfs_quota_enable() failed.

Also to follow the existing error handling behavior, abort the
transaction when the memory preallocation failed.

Reported-by: syzbot+947286c775f432b073a8@syzkaller.appspotmail.com
Link: https://lore.kernel.org/linux-btrfs/6ac5a5e1.9ad129c8.3ce5b3.0010.GAE@google.com/
Closes: https://syzkaller.appspot.com/bug?extid=947286c775f432b073a8
Signed-off-by: Yalagada Pavan Kumar <pavankumaryalagada@gmail.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
[ Change the commit message to include a proper analysis. ]
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/qgroup.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index cf8dfd5c692b..a0651fbfe778 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1207,6 +1207,7 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info,
 	prealloc = kzalloc_obj(*prealloc, GFP_NOFS);
 	if (!prealloc) {
 		ret = -ENOMEM;
+		btrfs_abort_transaction(trans, ret);
 		goto out;
 	}
 	qgroup = add_qgroup_rb(fs_info, prealloc, BTRFS_FS_TREE_OBJECTID);
@@ -1296,6 +1297,12 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info,
 		 * sysfs entries.
 		 */
 		btrfs_free_qgroup_config(fs_info);
+
+		if (quota_root) {
+			spin_lock(&fs_info->trans_lock);
+			list_del_init(&quota_root->dirty_list);
+			spin_unlock(&fs_info->trans_lock);
+		}
 		btrfs_put_root(quota_root);
 	}
 	mutex_unlock(&fs_info->qgroup_ioctl_lock);
-- 
2.55.0