FAILED: patch "[PATCH] btrfs: prevent deleting the wrong subvolume by ID" failed to apply to 6.6-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.6-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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 1960146913b31b288ed2cd607d103ee3b41681d4
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261109201050-failed-6.6-1960146913b3@kernel.org' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Thanks,
Sasha

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

From 1960146913b31b288ed2cd607d103ee3b41681d4 Mon Sep 17 00:00:00 2001
From: guolingxing <guolingxing@tju.edu.cn>
Date: Sun, 18 Oct 2026 15:38:10 +0000
Subject: [PATCH] btrfs: prevent deleting the wrong subvolume by ID

When deleting a subvolume by ID, btrfs_ioctl_snap_destroy() first
resolves the requested ID to a name, then looks up that name again
under the parent directory lock.

A concurrent rename can change which subvolume is associated with
the name between these operations. Since the deletion path does not
verify the ID of the resolved subvolume, it can delete a different
subvolume while leaving the requested one intact.

This was reproduced by repeatedly exchanging the names of two
subvolumes using renameat2(RENAME_EXCHANGE) while deleting one of
them by ID. The wrong subvolume was deleted in 9 out of 14 independent
tests.

Fix this by checking that the resolved subvolume ID matches the
requested ID while holding the parent directory lock. Return -EAGAIN
on a mismatch so that userspace can retry the operation instead of
being told that the requested subvolume does not exist.

Fixes: 949964c92843 ("btrfs: add new BTRFS_IOC_SNAP_DESTROY_V2 ioctl")
CC: stable@vger.kernel.org
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: guolingxing <guolingxing@tju.edu.cn>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/ioctl.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 43a945345cbe1..847fdc19bd402 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2393,6 +2393,17 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 
 	inode = d_inode(dentry);
 	dest = BTRFS_I(inode)->root;
+
+	/*
+	 * A concurrent rename may have changed which subvolume the name
+	 * refers to. Verify that the resolved ID still matches the requested ID.
+	 */
+	if (destroy_v2 && (vol_args2->flags & BTRFS_SUBVOL_SPEC_BY_ID) &&
+	    btrfs_root_id(dest) != vol_args2->subvolid) {
+		ret = -EAGAIN;
+		goto out_end_removing;
+	}
+
 	if (!capable(CAP_SYS_ADMIN)) {
 		/*
 		 * Regular user.  Only allow this with a special mount
-- 
2.53.0