4.19-stable review patch. If anyone has any objections, please let me know.
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From: Filipe Manana fdmanana@suse.com
commit 552f0329c75b3e1d7f9bb8c9e421d37403f192cd upstream.
We have a race between enabling quotas end subvolume creation that cause subvolume creation to fail with -EINVAL, and the following diagram shows how it happens:
CPU 0 CPU 1
btrfs_ioctl() btrfs_ioctl_quota_ctl() btrfs_quota_enable() mutex_lock(fs_info->qgroup_ioctl_lock)
btrfs_ioctl() create_subvol() btrfs_qgroup_inherit() -> save fs_info->quota_root into quota_root -> stores a NULL value -> tries to lock the mutex qgroup_ioctl_lock -> blocks waiting for the task at CPU0
-> sets BTRFS_FS_QUOTA_ENABLED in fs_info -> sets quota_root in fs_info->quota_root (non-NULL value)
mutex_unlock(fs_info->qgroup_ioctl_lock)
-> checks quota enabled flag is set -> returns -EINVAL because fs_info->quota_root was NULL before it acquired the mutex qgroup_ioctl_lock -> ioctl returns -EINVAL
Returning -EINVAL to user space will be confusing if all the arguments passed to the subvolume creation ioctl were valid.
Fix it by grabbing the value from fs_info->quota_root after acquiring the mutex.
CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Qu Wenruo wqu@suse.com Signed-off-by: Filipe Manana fdmanana@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/qgroup.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -2244,7 +2244,7 @@ int btrfs_qgroup_inherit(struct btrfs_tr int i; u64 *i_qgroups; struct btrfs_fs_info *fs_info = trans->fs_info; - struct btrfs_root *quota_root = fs_info->quota_root; + struct btrfs_root *quota_root; struct btrfs_qgroup *srcgroup; struct btrfs_qgroup *dstgroup; u32 level_size = 0; @@ -2254,6 +2254,7 @@ int btrfs_qgroup_inherit(struct btrfs_tr if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags)) goto out;
+ quota_root = fs_info->quota_root; if (!quota_root) { ret = -EINVAL; goto out;