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Don't propagate mounts into detached trees

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All versions up to 6.14 did not propagate mount events into detached
tree.  Shortly after 6.14 a merge of vfs-6.15-rc1.mount.namespace
(130e696aa6) has changed that.

Unfortunately, that has caused userland regressions (reported in
https://lore.kernel.org/all/CAOYeF9WQhFDe+BGW=Dp5fK8oRy5AgZ6zokVyTj1Wp4EUiYgt4w@mail.gmail.com/)

Straight revert wouldn't be an option - in particular, the variant in 6.14
had a bug that got fixed in d1ddc6f1d9 ("fix IS_MNT_PROPAGATING uses")
and we don't want to bring the bug back.

This is a modification of manual revert posted by Christian, with changes
needed to avoid reintroducing the breakage in scenario described in
d1ddc6f1d9.

Cc: stable@vger.kernel.org
Reported-by: Allison Karlitskaya <lis@redhat.com>
Tested-by: Allison Karlitskaya <lis@redhat.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Co-developed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2025-05-23 19:20:36 -04:00
parent d1ddc6f1d9
commit 3b5260d12b
3 changed files with 4 additions and 20 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

5
fs/mount.h
View file

@ -7,10 +7,6 @@
extern struct list_head notify_list; extern struct list_head notify_list;
typedef __u32 __bitwise mntns_flags_t;
#define MNTNS_PROPAGATING ((__force mntns_flags_t)(1 << 0))
struct mnt_namespace { struct mnt_namespace {
struct ns_common ns; struct ns_common ns;
struct mount * root; struct mount * root;
@ -37,7 +33,6 @@ struct mnt_namespace {
struct rb_node mnt_ns_tree_node; /* node in the mnt_ns_tree */ struct rb_node mnt_ns_tree_node; /* node in the mnt_ns_tree */
struct list_head mnt_ns_list; /* entry in the sequential list of mounts namespace */ struct list_head mnt_ns_list; /* entry in the sequential list of mounts namespace */
refcount_t passive; /* number references not pinning @mounts */ refcount_t passive; /* number references not pinning @mounts */
mntns_flags_t mntns_flags;
} __randomize_layout; } __randomize_layout;
struct mnt_pcp { struct mnt_pcp {

15
fs/namespace.c
View file

@ -3648,7 +3648,7 @@ static int do_move_mount(struct path *old_path,
if (!(attached ? check_mnt(old) : is_anon_ns(ns))) if (!(attached ? check_mnt(old) : is_anon_ns(ns)))
goto out; goto out;
if (is_anon_ns(ns)) { if (is_anon_ns(ns) && ns == p->mnt_ns) {
/* /*
* Ending up with two files referring to the root of the * Ending up with two files referring to the root of the
* same anonymous mount namespace would cause an error * same anonymous mount namespace would cause an error
@ -3656,16 +3656,7 @@ static int do_move_mount(struct path *old_path,
* twice into the mount tree which would be rejected * twice into the mount tree which would be rejected
* later. But be explicit about it right here. * later. But be explicit about it right here.
*/ */
if ((is_anon_ns(p->mnt_ns) && ns == p->mnt_ns)) goto out;
goto out;
/*
* If this is an anonymous mount tree ensure that mount
* propagation can detect mounts that were just
* propagated to the target mount tree so we don't
* propagate onto them.
*/
ns->mntns_flags |= MNTNS_PROPAGATING;
} else if (is_anon_ns(p->mnt_ns)) { } else if (is_anon_ns(p->mnt_ns)) {
/* /*
* Don't allow moving an attached mount tree to an * Don't allow moving an attached mount tree to an
@ -3722,8 +3713,6 @@ static int do_move_mount(struct path *old_path,
if (attached) if (attached)
put_mountpoint(old_mp); put_mountpoint(old_mp);
out: out:
if (is_anon_ns(ns))
ns->mntns_flags &= ~MNTNS_PROPAGATING;
unlock_mount(mp); unlock_mount(mp);
if (!err) { if (!err) {
if (attached) { if (attached) {

4
fs/pnode.c
View file

@ -231,8 +231,8 @@ static int propagate_one(struct mount *m, struct mountpoint *dest_mp)
/* skip if mountpoint isn't visible in m */ /* skip if mountpoint isn't visible in m */
if (!is_subdir(dest_mp->m_dentry, m->mnt.mnt_root)) if (!is_subdir(dest_mp->m_dentry, m->mnt.mnt_root))
return 0; return 0;
/* skip if m is in the anon_ns we are emptying */ /* skip if m is in the anon_ns */
if (m->mnt_ns->mntns_flags & MNTNS_PROPAGATING) if (is_anon_ns(m->mnt_ns))
return 0; return 0;
if (peers(m, last_dest)) { if (peers(m, last_dest)) {