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From: Christian Brauner <brauner@kernel.org>
To: Christoph Hellwig <hch@lst.de>, Chris Mason <clm@fb.com>,
	Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>,
	Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-btrfs@vger.kernel.org,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Christoph Hellwig <hch@infradead.org>
Subject: [PATCH v2 15/21] btrfs/ioctl: relax restrictions for BTRFS_IOC_SNAP_DESTROY_V2 with subvolids
Date: Mon, 19 Jul 2021 13:10:46 +0200	[thread overview]
Message-ID: <20210719111052.1626299-16-brauner@kernel.org> (raw)
In-Reply-To: <20210719111052.1626299-1-brauner@kernel.org>

From: Christian Brauner <christian.brauner@ubuntu.com>

So far we prevented the deletion of subvolumes and snapshots using subvolume
ids possible with the BTRFS_SUBVOL_SPEC_BY_ID flag.
This restriction is necessary on idmapped mounts as this allows filesystem wide
subvolume and snapshot deletions and thus can escape the scope of what's
exposed under the mount identified by the fd passed with the ioctl.

Deletion by subvolume id works by looking for an alias of the parent of the
subvolume or snapshot to be deleted. The parent alias can be anywhere in the
filesystem. However, as long as the alias of the parent that is found is the
same as the one identified by the file descriptor passed through the ioctl we
can allow the deletion.

Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Sterba <dsterba@suse.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
unchanged
---
 fs/btrfs/ioctl.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 5416b0c0ee7a..72045ae30d1c 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2944,17 +2944,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 			if (err)
 				goto out;
 		} else {
-			/*
-			 * Deleting by subvolume id can be used to delete
-			 * subvolumes/snapshots anywhere in the filesystem.
-			 * Ensure that users can't abuse idmapped mounts of
-			 * btrfs subvolumes/snapshots to perform operations in
-			 * the whole filesystem.
-			 */
-			if (mnt_userns != &init_user_ns) {
-				err = -EINVAL;
-				goto out;
-			}
+			struct inode *old_dir;
 
 			if (vol_args2->subvolid < BTRFS_FIRST_FREE_OBJECTID) {
 				err = -EINVAL;
@@ -2992,6 +2982,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 				err = PTR_ERR(parent);
 				goto out_drop_write;
 			}
+			old_dir = dir;
 			dir = d_inode(parent);
 
 			/*
@@ -3002,6 +2993,20 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 			 */
 			destroy_parent = true;
 
+			/*
+			 * On idmapped mounts, deletion via subvolid is
+			 * restricted to subvolumes that are immediate
+			 * ancestors of the inode referenced by the file
+			 * descriptor in the ioctl. Otherwise the idmapping
+			 * could potentially be abused to delete subvolumes
+			 * anywhere in the filesystem the user wouldn't be able
+			 * to delete without an idmapped mount.
+			 */
+			if (old_dir != dir && mnt_userns != &init_user_ns) {
+				err = -EINVAL;
+				goto free_parent;
+			}
+
 			subvol_name_ptr = btrfs_get_subvol_name_from_objectid(
 						fs_info, vol_args2->subvolid);
 			if (IS_ERR(subvol_name_ptr)) {
-- 
2.30.2


  parent reply	other threads:[~2021-07-19 11:11 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-19 11:10 [PATCH v2 00/21] btrfs: support idmapped mounts Christian Brauner
2021-07-19 11:10 ` [PATCH v2 01/21] namei: add mapping aware lookup helper Christian Brauner
2021-07-19 11:10 ` [PATCH v2 02/21] btrfs/inode: handle idmaps in btrfs_new_inode() Christian Brauner
2021-07-19 11:10 ` [PATCH v2 03/21] btrfs/inode: allow idmapped rename iop Christian Brauner
2021-07-19 11:10 ` [PATCH v2 04/21] btrfs/inode: allow idmapped getattr iop Christian Brauner
2021-07-19 11:10 ` [PATCH v2 05/21] btrfs/inode: allow idmapped mknod iop Christian Brauner
2021-07-19 11:10 ` [PATCH v2 06/21] btrfs/inode: allow idmapped create iop Christian Brauner
2021-07-19 11:10 ` [PATCH v2 07/21] btrfs/inode: allow idmapped mkdir iop Christian Brauner
2021-07-19 11:10 ` [PATCH v2 08/21] btrfs/inode: allow idmapped symlink iop Christian Brauner
2021-07-19 11:10 ` [PATCH v2 09/21] btrfs/inode: allow idmapped tmpfile iop Christian Brauner
2021-07-19 11:10 ` [PATCH v2 10/21] btrfs/inode: allow idmapped setattr iop Christian Brauner
2021-07-19 11:10 ` [PATCH v2 11/21] btrfs/inode: allow idmapped permission iop Christian Brauner
2021-07-19 11:10 ` [PATCH v2 12/21] btrfs/ioctl: check whether fs{g,u}id are mapped during subvolume creation Christian Brauner
2021-07-19 11:10 ` [PATCH v2 13/21] btrfs/inode: allow idmapped BTRFS_IOC_{SNAP,SUBVOL}_CREATE{_V2} ioctl Christian Brauner
2021-07-19 11:10 ` [PATCH v2 14/21] btrfs/ioctl: allow idmapped BTRFS_IOC_SNAP_DESTROY{_V2} ioctl Christian Brauner
2021-07-21 14:15   ` David Sterba
2021-07-21 15:48     ` Christian Brauner
2021-07-19 11:10 ` Christian Brauner [this message]
2021-07-19 11:10 ` [PATCH v2 16/21] btrfs/ioctl: allow idmapped BTRFS_IOC_SET_RECEIVED_SUBVOL{_32} ioctl Christian Brauner
2021-07-19 11:10 ` [PATCH v2 17/21] btrfs/ioctl: allow idmapped BTRFS_IOC_SUBVOL_SETFLAGS ioctl Christian Brauner
2021-07-19 11:10 ` [PATCH v2 18/21] btrfs/ioctl: allow idmapped BTRFS_IOC_INO_LOOKUP_USER ioctl Christian Brauner
2021-07-19 11:10 ` [PATCH v2 19/21] btrfs/acl: handle idmapped mounts Christian Brauner
2021-07-19 11:10 ` [PATCH v2 20/21] btrfs/super: allow idmapped btrfs Christian Brauner
2021-07-19 11:10 ` [PATCH v2 21/21] btrfs/242: introduce btrfs specific idmapped mounts tests Christian Brauner
2021-07-19 15:11 ` [PATCH v2 00/21] btrfs: support idmapped mounts Josef Bacik

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