The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x e1249667750399a48cafcf5945761d39fa584edf # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025081832-drainable-observant-d242@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e1249667750399a48cafcf5945761d39fa584edf Mon Sep 17 00:00:00 2001 From: Filipe Manana fdmanana@suse.com Date: Mon, 30 Jun 2025 13:19:20 +0100 Subject: [PATCH] btrfs: qgroup: fix race between quota disable and quota rescan ioctl

There's a race between a task disabling quotas and another running the rescan ioctl that can result in a use-after-free of qgroup records from the fs_info->qgroup_tree rbtree.

This happens as follows:

1) Task A enters btrfs_ioctl_quota_rescan() -> btrfs_qgroup_rescan();

2) Task B enters btrfs_quota_disable() and calls btrfs_qgroup_wait_for_completion(), which does nothing because at that point fs_info->qgroup_rescan_running is false (it wasn't set yet by task A);

3) Task B calls btrfs_free_qgroup_config() which starts freeing qgroups from fs_info->qgroup_tree without taking the lock fs_info->qgroup_lock;

4) Task A enters qgroup_rescan_zero_tracking() which starts iterating the fs_info->qgroup_tree tree while holding fs_info->qgroup_lock, but task B is freeing qgroup records from that tree without holding the lock, resulting in a use-after-free.

Fix this by taking fs_info->qgroup_lock at btrfs_free_qgroup_config(). Also at btrfs_qgroup_rescan() don't start the rescan worker if quotas were already disabled.

Reported-by: cen zhang zzzccc427@gmail.com Link: https://lore.kernel.org/linux-btrfs/CAFRLqsV+cMDETFuzqdKSHk_FDm6tneea45krsHq... CC: stable@vger.kernel.org # 6.1+ Reviewed-by: Boris Burkov boris@bur.io Reviewed-by: Qu Wenruo wqu@suse.com Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index b83d9534adae..310ca2dd9f24 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -636,22 +636,30 @@ bool btrfs_check_quota_leak(const struct btrfs_fs_info *fs_info)

/* * This is called from close_ctree() or open_ctree() or btrfs_quota_disable(), - * first two are in single-threaded paths.And for the third one, we have set - * quota_root to be null with qgroup_lock held before, so it is safe to clean - * up the in-memory structures without qgroup_lock held. + * first two are in single-threaded paths. */ void btrfs_free_qgroup_config(struct btrfs_fs_info *fs_info) { struct rb_node *n; struct btrfs_qgroup *qgroup;

+ /* + * btrfs_quota_disable() can be called concurrently with + * btrfs_qgroup_rescan() -> qgroup_rescan_zero_tracking(), so take the + * lock. + */ + spin_lock(&fs_info->qgroup_lock); while ((n = rb_first(&fs_info->qgroup_tree))) { qgroup = rb_entry(n, struct btrfs_qgroup, node); rb_erase(n, &fs_info->qgroup_tree); __del_qgroup_rb(qgroup); + spin_unlock(&fs_info->qgroup_lock); btrfs_sysfs_del_one_qgroup(fs_info, qgroup); kfree(qgroup); + spin_lock(&fs_info->qgroup_lock); } + spin_unlock(&fs_info->qgroup_lock); + /* * We call btrfs_free_qgroup_config() when unmounting * filesystem and disabling quota, so we set qgroup_ulist @@ -4036,12 +4044,21 @@ btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info) qgroup_rescan_zero_tracking(fs_info);

mutex_lock(&fs_info->qgroup_rescan_lock); - fs_info->qgroup_rescan_running = true; - btrfs_queue_work(fs_info->qgroup_rescan_workers, - &fs_info->qgroup_rescan_work); + /* + * The rescan worker is only for full accounting qgroups, check if it's + * enabled as it is pointless to queue it otherwise. A concurrent quota + * disable may also have just cleared BTRFS_FS_QUOTA_ENABLED. + */ + if (btrfs_qgroup_full_accounting(fs_info)) { + fs_info->qgroup_rescan_running = true; + btrfs_queue_work(fs_info->qgroup_rescan_workers, + &fs_info->qgroup_rescan_work); + } else { + ret = -ENOTCONN; + } mutex_unlock(&fs_info->qgroup_rescan_lock);

- return 0; + return ret; }

int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info,