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[91.82.183.41]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438bd507e46sm1687245e9.21.2025.01.23.11.41.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jan 2025 11:41:14 -0800 (PST) From: Miklos Szeredi To: linux-fsdevel@vger.kernel.org Cc: Christian Brauner , Jan Kara , Amir Goldstein , Karel Zak , Lennart Poettering , Ian Kent , Al Viro , linux-security-module@vger.kernel.org, Paul Moore Subject: [PATCH v4 3/4] vfs: add notifications for mount attach and detach Date: Thu, 23 Jan 2025 20:41:06 +0100 Message-ID: <20250123194108.1025273-4-mszeredi@redhat.com> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20250123194108.1025273-1-mszeredi@redhat.com> References: <20250123194108.1025273-1-mszeredi@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Add notifications for attaching and detaching mounts to fs/namespace.c Signed-off-by: Miklos Szeredi --- fs/mount.h | 20 +++++++++++++ fs/namespace.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++- fs/pnode.c | 4 ++- 3 files changed, 101 insertions(+), 2 deletions(-) diff --git a/fs/mount.h b/fs/mount.h index 9689e7bf4501..7dd22a226a6e 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -5,6 +5,8 @@ #include #include +extern struct list_head notify_list; + struct mnt_namespace { struct ns_common ns; struct mount * root; @@ -72,6 +74,8 @@ struct mount { #ifdef CONFIG_FSNOTIFY struct fsnotify_mark_connector __rcu *mnt_fsnotify_marks; __u32 mnt_fsnotify_mask; + struct list_head to_notify; /* need to queue notification */ + struct mnt_namespace *prev_ns; /* previous namespace (NULL if none) */ #endif int mnt_id; /* mount identifier, reused */ u64 mnt_id_unique; /* mount ID unique until reboot */ @@ -175,4 +179,20 @@ static inline struct mnt_namespace *to_mnt_ns(struct ns_common *ns) return container_of(ns, struct mnt_namespace, ns); } +#ifdef CONFIG_FSNOTIFY +static inline void mnt_notify_add(struct mount *m) +{ + /* Optimize the case where there are no watches */ + if ((m->mnt_ns && m->mnt_ns->n_fsnotify_marks) || + (m->prev_ns && m->prev_ns->n_fsnotify_marks)) + list_add_tail(&m->to_notify, ¬ify_list); + else + m->prev_ns = m->mnt_ns; +} +#else +static inline void mnt_notify_add(struct mount *m) +{ +} +#endif + struct mnt_namespace *mnt_ns_from_dentry(struct dentry *dentry); diff --git a/fs/namespace.c b/fs/namespace.c index 4d9072fd1263..948348a37f6c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -79,6 +79,9 @@ static struct kmem_cache *mnt_cache __ro_after_init; static DECLARE_RWSEM(namespace_sem); static HLIST_HEAD(unmounted); /* protected by namespace_sem */ static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */ +#ifdef CONFIG_FSNOTIFY +LIST_HEAD(notify_list); /* protected by namespace_sem */ +#endif static DEFINE_RWLOCK(mnt_ns_tree_lock); static struct rb_root mnt_ns_tree = RB_ROOT; /* protected by mnt_ns_tree_lock */ @@ -145,6 +148,7 @@ static void mnt_ns_release(struct mnt_namespace *ns) /* keep alive for {list,stat}mount() */ if (refcount_dec_and_test(&ns->passive)) { + fsnotify_mntns_delete(ns); put_user_ns(ns->user_ns); kfree(ns); } @@ -1136,6 +1140,8 @@ static void mnt_add_to_ns(struct mnt_namespace *ns, struct mount *mnt) } rb_link_node(&mnt->mnt_node, parent, link); rb_insert_color(&mnt->mnt_node, &ns->mounts); + + mnt_notify_add(mnt); } /* @@ -1683,6 +1689,50 @@ int may_umount(struct vfsmount *mnt) EXPORT_SYMBOL(may_umount); +#ifdef CONFIG_FSNOTIFY +static void mnt_notify(struct mount *p) +{ + if (!p->prev_ns && p->mnt_ns) { + fsnotify_mnt_attach(p->mnt_ns, &p->mnt); + } else if (p->prev_ns && !p->mnt_ns) { + fsnotify_mnt_detach(p->prev_ns, &p->mnt); + } else if (p->prev_ns == p->mnt_ns) { + fsnotify_mnt_move(p->mnt_ns, &p->mnt); + } else { + fsnotify_mnt_detach(p->prev_ns, &p->mnt); + fsnotify_mnt_attach(p->mnt_ns, &p->mnt); + } + p->prev_ns = p->mnt_ns; +} + +static void notify_mnt_list(void) +{ + struct mount *m, *tmp; + /* + * Notify about mounts that were added/reparented/detached/remain + * connected after unmount. + */ + list_for_each_entry_safe(m, tmp, ¬ify_list, to_notify) { + mnt_notify(m); + list_del_init(&m->to_notify); + } +} + +static bool need_notify_mnt_list(void) +{ + return !list_empty(¬ify_list); +} +#else +static void notify_mnt_list(void) +{ +} + +static bool need_notify_mnt_list(void) +{ + return false; +} +#endif + static void namespace_unlock(void) { struct hlist_head head; @@ -1693,7 +1743,18 @@ static void namespace_unlock(void) hlist_move_list(&unmounted, &head); list_splice_init(&ex_mountpoints, &list); - up_write(&namespace_sem); + if (need_notify_mnt_list()) { + /* + * No point blocking out concurrent readers while notifications + * are sent. This will also allow statmount()/listmount() to run + * concurrently. + */ + downgrade_write(&namespace_sem); + notify_mnt_list(); + up_read(&namespace_sem); + } else { + up_write(&namespace_sem); + } shrink_dentry_list(&list); @@ -1806,6 +1867,19 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how) change_mnt_propagation(p, MS_PRIVATE); if (disconnect) hlist_add_head(&p->mnt_umount, &unmounted); + + /* + * At this point p->mnt_ns is NULL, notification will be queued + * only if + * + * - p->prev_ns is non-NULL *and* + * - p->prev_ns->n_fsnotify_marks is non-NULL + * + * This will preclude queuing the mount if this is a cleanup + * after a failed copy_tree() or destruction of an anonymous + * namespace, etc. + */ + mnt_notify_add(p); } } @@ -2511,6 +2585,7 @@ static int attach_recursive_mnt(struct mount *source_mnt, dest_mp = smp; unhash_mnt(source_mnt); attach_mnt(source_mnt, top_mnt, dest_mp, beneath); + mnt_notify_add(source_mnt); touch_mnt_namespace(source_mnt->mnt_ns); } else { if (source_mnt->mnt_ns) { @@ -4426,6 +4501,8 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, list_del_init(&new_mnt->mnt_expire); put_mountpoint(root_mp); unlock_mount_hash(); + mnt_notify_add(root_mnt); + mnt_notify_add(new_mnt); chroot_fs_refs(&root, &new); error = 0; out4: diff --git a/fs/pnode.c b/fs/pnode.c index a799e0315cc9..d42b71c3567a 100644 --- a/fs/pnode.c +++ b/fs/pnode.c @@ -549,8 +549,10 @@ static void restore_mounts(struct list_head *to_restore) mp = parent->mnt_mp; parent = parent->mnt_parent; } - if (parent != mnt->mnt_parent) + if (parent != mnt->mnt_parent) { mnt_change_mountpoint(parent, mp, mnt); + mnt_notify_add(mnt); + } } }