Merge patch series "Support foreign mount namespace with statmount/listmount"

Josef Bacik <josef@toxicpanda.com> says:

Currently the only way to iterate over mount entries in mount namespaces that
aren't your own is to trawl through /proc in order to find /proc/$PID/mountinfo
for the mount namespace that you want.  This is hugely inefficient, so extend
both statmount() and listmount() to allow specifying a mount namespace id in
order to get to mounts in other mount namespaces.

There are a few components to this

1. Having a global index of the mount namespace based on the ->seq value in the
   mount namespace.  This gives us a unique identifier that isn't re-used.
2. Support looking up mount namespaces based on that unique identifier, and
   validating the user has permission to access the given mount namespace.
3. Provide a new ioctl() on nsfs in order to extract the unique identifier we
   can use for statmount() and listmount().

The code is relatively straightforward, and there is a selftest provided to
validate everything works properly.

This is based on vfs.all as of last week, so must be applied onto a tree that
has Christians error handling rework in this area.  If you wish you can pull the
tree directly here

https://github.com/josefbacik/linux/tree/listmount.combined

Christian and I collaborated on this series, which is why there's patches from
both of us in this series.

Christian Brauner (4):
  fs: relax permissions for listmount()
  fs: relax permissions for statmount()
  fs: Allow listmount() in foreign mount namespace
  fs: Allow statmount() in foreign mount namespace

Josef Bacik (4):
  fs: keep an index of current mount namespaces
  fs: export the mount ns id via statmount
  fs: add an ioctl to get the mnt ns id from nsfs
  selftests: add a test for the foreign mnt ns extensions

fs/mount.h                                    |   2 +
 fs/namespace.c                                | 240 ++++++++++--
 fs/nsfs.c                                     |  14 +
 include/uapi/linux/mount.h                    |   6 +-
 include/uapi/linux/nsfs.h                     |   2 +
 .../selftests/filesystems/statmount/Makefile  |   2 +-
 .../filesystems/statmount/statmount.h         |  46 +++
 .../filesystems/statmount/statmount_test.c    |  53 +--
 .../filesystems/statmount/statmount_test_ns.c | 360 ++++++++++++++++++
 9 files changed, 659 insertions(+), 66 deletions(-)
 create mode 100644 tools/testing/selftests/filesystems/statmount/statmount.h
 create mode 100644 tools/testing/selftests/filesystems/statmount/statmount_test_ns.c

Link: https://lore.kernel.org/r/cover.1719243756.git.josef@toxicpanda.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 7 insertions, 1 deletions

diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index 88d78de1519f..ee1559cd6764 100644
--- a/include/uapi/linux/mount.h
+++ b/include/uapi/linux/mount.h
@@ -172,7 +172,8 @@ struct statmount {
 	__u64 propagate_from;	/* Propagation from in current namespace */
 	__u32 mnt_root;		/* [str] Root of mount relative to root of fs */
 	__u32 mnt_point;	/* [str] Mountpoint relative to current root */
-	__u64 __spare2[50];
+	__u64 mnt_ns_id;	/* ID of the mount namespace */
+	__u64 __spare2[49];
 	char str[];		/* Variable size part containing strings */
 };
 
@@ -188,10 +189,12 @@ struct mnt_id_req {
 	__u32 spare;
 	__u64 mnt_id;
 	__u64 param;
+	__u64 mnt_ns_id;
 };
 
 /* List of all mnt_id_req versions. */
 #define MNT_ID_REQ_SIZE_VER0	24 /* sizeof first published struct */
+#define MNT_ID_REQ_SIZE_VER1	32 /* sizeof second published struct */
 
 /*
  * @mask bits for statmount(2)
@@ -202,6 +205,7 @@ struct mnt_id_req {
 #define STATMOUNT_MNT_ROOT		0x00000008U	/* Want/got mnt_root  */
 #define STATMOUNT_MNT_POINT		0x00000010U	/* Want/got mnt_point */
 #define STATMOUNT_FS_TYPE		0x00000020U	/* Want/got fs_type */
+#define STATMOUNT_MNT_NS_ID		0x00000040U	/* Want/got mnt_ns_id */
 
 /*
  * Special @mnt_id values that can be passed to listmount
diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
index a0c8552b64ee..56e8b1639b98 100644
--- a/include/uapi/linux/nsfs.h
+++ b/include/uapi/linux/nsfs.h
@@ -15,5 +15,7 @@
 #define NS_GET_NSTYPE		_IO(NSIO, 0x3)
 /* Get owner UID (in the caller's user namespace) for a user namespace */
 #define NS_GET_OWNER_UID	_IO(NSIO, 0x4)
+/* Get the id for a mount namespace */
+#define NS_GET_MNTNS_ID		_IO(NSIO, 0x5)
 
 #endif /* __LINUX_NSFS_H */