btrfs: fix race between accounting qgroup extents and removing a qgroup

When doing qgroup accounting for an extent, we take the spinlock
fs_info->qgroup_lock and then add qgroups to the local list (iterator)
named "qgroups". These qgroups are found in the fs_info->qgroup_tree
rbtree. After we're done, we unlock fs_info->qgroup_lock and then call
qgroup_iterator_nested_clean(), which will iterate over all the qgroups
added to the local list "qgroups" and then delete them from the list.
Deleting a qgroup from the list can however result in a use-after-free
if a qgroup remove operation happens after we unlock fs_info->qgroup_lock
and before or while we are at qgroup_iterator_nested_clean().

Fix this by calling qgroup_iterator_nested_clean() while still holding
the lock fs_info->qgroup_lock - we don't need it under the 'out' label
since before taking the lock the "qgroups" list is always empty. This
guarantees safety because btrfs_remove_qgroup() takes that lock before
removing a qgroup from the rbtree fs_info->qgroup_tree.

This was reported by syzbot with the following stack traces:

   BUG: KASAN: slab-use-after-free in __list_del_entry_valid_or_report+0x2f/0x130 lib/list_debug.c:49
   Read of size 8 at addr ffff888027e420b0 by task kworker/u4:3/48

   CPU: 1 PID: 48 Comm: kworker/u4:3 Not tainted 6.6.0-syzkaller-10396-g4652b8e4f3ff #0
   Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
   Workqueue: btrfs-qgroup-rescan btrfs_work_helper
   Call Trace:
    <TASK>
    __dump_stack lib/dump_stack.c:88 [inline]
    dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
    print_address_description mm/kasan/report.c:364 [inline]
    print_report+0x163/0x540 mm/kasan/report.c:475
    kasan_report+0x175/0x1b0 mm/kasan/report.c:588
    __list_del_entry_valid_or_report+0x2f/0x130 lib/list_debug.c:49
    __list_del_entry_valid include/linux/list.h:124 [inline]
    __list_del_entry include/linux/list.h:215 [inline]
    list_del_init include/linux/list.h:287 [inline]
    qgroup_iterator_nested_clean fs/btrfs/qgroup.c:2623 [inline]
    btrfs_qgroup_account_extent+0x18b/0x1150 fs/btrfs/qgroup.c:2883
    qgroup_rescan_leaf fs/btrfs/qgroup.c:3543 [inline]
    btrfs_qgroup_rescan_worker+0x1078/0x1c60 fs/btrfs/qgroup.c:3604
    btrfs_work_helper+0x37c/0xbd0 fs/btrfs/async-thread.c:315
    process_one_work kernel/workqueue.c:2630 [inline]
    process_scheduled_works+0x90f/0x1400 kernel/workqueue.c:2703
    worker_thread+0xa5f/0xff0 kernel/workqueue.c:2784
    kthread+0x2d3/0x370 kernel/kthread.c:388
    ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
    ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
    </TASK>

   Allocated by task 6355:
    kasan_save_stack mm/kasan/common.c:45 [inline]
    kasan_set_track+0x4f/0x70 mm/kasan/common.c:52
    ____kasan_kmalloc mm/kasan/common.c:374 [inline]
    __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:383
    kmalloc include/linux/slab.h:600 [inline]
    kzalloc include/linux/slab.h:721 [inline]
    btrfs_quota_enable+0xee9/0x2060 fs/btrfs/qgroup.c:1209
    btrfs_ioctl_quota_ctl+0x143/0x190 fs/btrfs/ioctl.c:3705
    vfs_ioctl fs/ioctl.c:51 [inline]
    __do_sys_ioctl fs/ioctl.c:871 [inline]
    __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
    do_syscall_x64 arch/x86/entry/common.c:51 [inline]
    do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
    entry_SYSCALL_64_after_hwframe+0x63/0x6b

   Freed by task 6355:
    kasan_save_stack mm/kasan/common.c:45 [inline]
    kasan_set_track+0x4f/0x70 mm/kasan/common.c:52
    kasan_save_free_info+0x28/0x40 mm/kasan/generic.c:522
    ____kasan_slab_free+0xd6/0x120 mm/kasan/common.c:236
    kasan_slab_free include/linux/kasan.h:164 [inline]
    slab_free_hook mm/slub.c:1800 [inline]
    slab_free_freelist_hook mm/slub.c:1826 [inline]
    slab_free mm/slub.c:3809 [inline]
    __kmem_cache_free+0x263/0x3a0 mm/slub.c:3822
    btrfs_remove_qgroup+0x764/0x8c0 fs/btrfs/qgroup.c:1787
    btrfs_ioctl_qgroup_create+0x185/0x1e0 fs/btrfs/ioctl.c:3811
    vfs_ioctl fs/ioctl.c:51 [inline]
    __do_sys_ioctl fs/ioctl.c:871 [inline]
    __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
    do_syscall_x64 arch/x86/entry/common.c:51 [inline]
    do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
    entry_SYSCALL_64_after_hwframe+0x63/0x6b

   Last potentially related work creation:
    kasan_save_stack+0x3f/0x60 mm/kasan/common.c:45
    __kasan_record_aux_stack+0xad/0xc0 mm/kasan/generic.c:492
    __call_rcu_common kernel/rcu/tree.c:2667 [inline]
    call_rcu+0x167/0xa70 kernel/rcu/tree.c:2781
    kthread_worker_fn+0x4ba/0xa90 kernel/kthread.c:823
    kthread+0x2d3/0x370 kernel/kthread.c:388
    ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
    ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

   Second to last potentially related work creation:
    kasan_save_stack+0x3f/0x60 mm/kasan/common.c:45
    __kasan_record_aux_stack+0xad/0xc0 mm/kasan/generic.c:492
    __call_rcu_common kernel/rcu/tree.c:2667 [inline]
    call_rcu+0x167/0xa70 kernel/rcu/tree.c:2781
    kthread_worker_fn+0x4ba/0xa90 kernel/kthread.c:823
    kthread+0x2d3/0x370 kernel/kthread.c:388
    ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
    ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

   The buggy address belongs to the object at ffff888027e42000
    which belongs to the cache kmalloc-512 of size 512
   The buggy address is located 176 bytes inside of
    freed 512-byte region [ffff888027e42000, ffff888027e42200)

   The buggy address belongs to the physical page:
   page:ffffea00009f9000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x27e40
   head:ffffea00009f9000 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
   flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
   page_type: 0xffffffff()
   raw: 00fff00000000840 ffff888012c41c80 ffffea0000a5ba00 dead000000000002
   raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
   page dumped because: kasan: bad access detected
   page_owner tracks the page as allocated
   page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 4514, tgid 4514 (udevadm), ts 24598439480, free_ts 23755696267
    set_page_owner include/linux/page_owner.h:31 [inline]
    post_alloc_hook+0x1e6/0x210 mm/page_alloc.c:1536
    prep_new_page mm/page_alloc.c:1543 [inline]
    get_page_from_freelist+0x31db/0x3360 mm/page_alloc.c:3170
    __alloc_pages+0x255/0x670 mm/page_alloc.c:4426
    alloc_slab_page+0x6a/0x160 mm/slub.c:1870
    allocate_slab mm/slub.c:2017 [inline]
    new_slab+0x84/0x2f0 mm/slub.c:2070
    ___slab_alloc+0xc85/0x1310 mm/slub.c:3223
    __slab_alloc mm/slub.c:3322 [inline]
    __slab_alloc_node mm/slub.c:3375 [inline]
    slab_alloc_node mm/slub.c:3468 [inline]
    __kmem_cache_alloc_node+0x19d/0x270 mm/slub.c:3517
    kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
    kmalloc include/linux/slab.h:600 [inline]
    kzalloc include/linux/slab.h:721 [inline]
    kernfs_fop_open+0x3e7/0xcc0 fs/kernfs/file.c:670
    do_dentry_open+0x8fd/0x1590 fs/open.c:948
    do_open fs/namei.c:3622 [inline]
    path_openat+0x2845/0x3280 fs/namei.c:3779
    do_filp_open+0x234/0x490 fs/namei.c:3809
    do_sys_openat2+0x13e/0x1d0 fs/open.c:1440
    do_sys_open fs/open.c:1455 [inline]
    __do_sys_openat fs/open.c:1471 [inline]
    __se_sys_openat fs/open.c:1466 [inline]
    __x64_sys_openat+0x247/0x290 fs/open.c:1466
    do_syscall_x64 arch/x86/entry/common.c:51 [inline]
    do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
    entry_SYSCALL_64_after_hwframe+0x63/0x6b
   page last free stack trace:
    reset_page_owner include/linux/page_owner.h:24 [inline]
    free_pages_prepare mm/page_alloc.c:1136 [inline]
    free_unref_page_prepare+0x8c3/0x9f0 mm/page_alloc.c:2312
    free_unref_page+0x37/0x3f0 mm/page_alloc.c:2405
    discard_slab mm/slub.c:2116 [inline]
    __unfreeze_partials+0x1dc/0x220 mm/slub.c:2655
    put_cpu_partial+0x17b/0x250 mm/slub.c:2731
    __slab_free+0x2b6/0x390 mm/slub.c:3679
    qlink_free mm/kasan/quarantine.c:166 [inline]
    qlist_free_all+0x75/0xe0 mm/kasan/quarantine.c:185
    kasan_quarantine_reduce+0x14b/0x160 mm/kasan/quarantine.c:292
    __kasan_slab_alloc+0x23/0x70 mm/kasan/common.c:305
    kasan_slab_alloc include/linux/kasan.h:188 [inline]
    slab_post_alloc_hook+0x67/0x3d0 mm/slab.h:762
    slab_alloc_node mm/slub.c:3478 [inline]
    slab_alloc mm/slub.c:3486 [inline]
    __kmem_cache_alloc_lru mm/slub.c:3493 [inline]
    kmem_cache_alloc+0x104/0x2c0 mm/slub.c:3502
    getname_flags+0xbc/0x4f0 fs/namei.c:140
    do_sys_openat2+0xd2/0x1d0 fs/open.c:1434
    do_sys_open fs/open.c:1455 [inline]
    __do_sys_openat fs/open.c:1471 [inline]
    __se_sys_openat fs/open.c:1466 [inline]
    __x64_sys_openat+0x247/0x290 fs/open.c:1466
    do_syscall_x64 arch/x86/entry/common.c:51 [inline]
    do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
    entry_SYSCALL_64_after_hwframe+0x63/0x6b

   Memory state around the buggy address:
    ffff888027e41f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
    ffff888027e42000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
   >ffff888027e42080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                        ^
    ffff888027e42100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
    ffff888027e42180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

Reported-by: syzbot+e0b615318f8fcfc01ceb@syzkaller.appspotmail.com
Fixes: dce28769a33a ("btrfs: qgroup: use qgroup_iterator_nested to in qgroup_update_refcnt()")
CC: stable@vger.kernel.org # 6.6
Link: https://lore.kernel.org/linux-btrfs/00000000000091a5b2060936bf6d@google.com/
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index edb84cc03237..e48eba7e9379 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2875,12 +2875,18 @@ int btrfs_qgroup_account_extent(struct btrfs_trans_handle *trans, u64 bytenr,
 			       num_bytes, seq);
 
 	/*
+	 * We're done using the iterator, release all its qgroups while holding
+	 * fs_info->qgroup_lock so that we don't race with btrfs_remove_qgroup()
+	 * and trigger use-after-free accesses to qgroups.
+	 */
+	qgroup_iterator_nested_clean(&qgroups);
+
+	/*
 	 * Bump qgroup_seq to avoid seq overlap
 	 */
 	fs_info->qgroup_seq += max(nr_old_roots, nr_new_roots) + 1;
 	spin_unlock(&fs_info->qgroup_lock);
 out_free:
-	qgroup_iterator_nested_clean(&qgroups);
 	ulist_free(old_roots);
 	ulist_free(new_roots);
 	return ret;