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btrfs: avoid copying BTRFS_ROOT_SUBVOL_DEAD flag to snapshot of subvolume being deleted 

Sweet Tea spotted a race between subvolume deletion and snapshotting
that can result in the root item for the snapshot having the
BTRFS_ROOT_SUBVOL_DEAD flag set. The race is:

Thread 1                                      | Thread 2
----------------------------------------------|----------
btrfs_delete_subvolume                        |
  btrfs_set_root_flags(BTRFS_ROOT_SUBVOL_DEAD)|
                                              |btrfs_mksubvol
                                              |  down_read(subvol_sem)
                                              |  create_snapshot
                                              |    ...
                                              |    create_pending_snapshot
                                              |      copy root item from source
  down_write(subvol_sem)                      |

This flag is only checked in send and swap activate, which this would
cause to fail mysteriously.

create_snapshot() now checks the root refs to reject a deleted
subvolume, so we can fix this by locking subvol_sem earlier so that the
BTRFS_ROOT_SUBVOL_DEAD flag and the root refs are updated atomically.

CC: stable@vger.kernel.org # 4.14+
Reported-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Omar Sandoval 2024-01-04 11:48:47 -08:00 committed by David Sterba
parent 7081929ab2
commit 3324d05478
1 changed files with 13 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
fs/btrfs/inode.c
View File

@ -4458,6 +4458,8 @@ int btrfs_delete_subvolume(struct btrfs_inode *dir, struct dentry *dentry)
u64 root_flags;
int ret;
down_write(&fs_info->subvol_sem);
/*
* Don't allow to delete a subvolume with send in progress. This is
* inside the inode lock so the error handling that has to drop the bit
@ -4469,25 +4471,25 @@ int btrfs_delete_subvolume(struct btrfs_inode *dir, struct dentry *dentry)
btrfs_warn(fs_info,
"attempt to delete subvolume %llu during send",
dest->root_key.objectid);
return -EPERM;
ret = -EPERM;
goto out_up_write;
}
if (atomic_read(&dest->nr_swapfiles)) {
spin_unlock(&dest->root_item_lock);
btrfs_warn(fs_info,
"attempt to delete subvolume %llu with active swapfile",
root->root_key.objectid);
return -EPERM;
ret = -EPERM;
goto out_up_write;
}
root_flags = btrfs_root_flags(&dest->root_item);
btrfs_set_root_flags(&dest->root_item,
root_flags | BTRFS_ROOT_SUBVOL_DEAD);
spin_unlock(&dest->root_item_lock);
down_write(&fs_info->subvol_sem);
ret = may_destroy_subvol(dest);
if (ret)
goto out_up_write;
goto out_undead;
btrfs_init_block_rsv(&block_rsv, BTRFS_BLOCK_RSV_TEMP);
/*
@ -4497,7 +4499,7 @@ int btrfs_delete_subvolume(struct btrfs_inode *dir, struct dentry *dentry)
*/
ret = btrfs_subvolume_reserve_metadata(root, &block_rsv, 5, true);
if (ret)
goto out_up_write;
goto out_undead;
trans = btrfs_start_transaction(root, 0);
if (IS_ERR(trans)) {
@ -4563,15 +4565,17 @@ out_end_trans:
inode->i_flags |= S_DEAD;
out_release:
btrfs_subvolume_release_metadata(root, &block_rsv);
out_up_write:
up_write(&fs_info->subvol_sem);
out_undead:
if (ret) {
spin_lock(&dest->root_item_lock);
root_flags = btrfs_root_flags(&dest->root_item);
btrfs_set_root_flags(&dest->root_item,
root_flags & ~BTRFS_ROOT_SUBVOL_DEAD);
spin_unlock(&dest->root_item_lock);
} else {
}
out_up_write:
up_write(&fs_info->subvol_sem);
if (!ret) {
d_invalidate(dentry);
btrfs_prune_dentries(dest);
ASSERT(dest->send_in_progress == 0);