@@ -439,3 +439,4 @@
432 i386 fsmount sys_fsmount __ia32_sys_fsmount
433 i386 fspick sys_fspick __ia32_sys_fspick
434 i386 fsinfo sys_fsinfo __ia32_sys_fsinfo
+435 i386 watch_mount sys_watch_mount __ia32_sys_watch_mount
@@ -356,6 +356,7 @@
432 common fsmount __x64_sys_fsmount
433 common fspick __x64_sys_fspick
434 common fsinfo __x64_sys_fsinfo
+435 common watch_mount __x64_sys_watch_mount
#
# x32-specific system call numbers start at 512 to avoid cache impact
@@ -121,6 +121,15 @@ source "fs/crypto/Kconfig"
source "fs/notify/Kconfig"
+config MOUNT_NOTIFICATIONS
+ bool "Mount topology change notifications"
+ select WATCH_QUEUE
+ help
+ This option provides support for getting change notifications on the
+ mount tree topology. This makes use of the /dev/watch_queue misc
+ device to handle the notification buffer and provides the
+ mount_notify() system call to enable/disable watchpoints.
+
source "fs/quota/Kconfig"
source "fs/autofs/Kconfig"
@@ -131,3 +131,4 @@ obj-$(CONFIG_F2FS_FS) += f2fs/
obj-$(CONFIG_CEPH_FS) += ceph/
obj-$(CONFIG_PSTORE) += pstore/
obj-$(CONFIG_EFIVAR_FS) += efivarfs/
+obj-$(CONFIG_MOUNT_NOTIFICATIONS) += mount_notify.o
@@ -4,6 +4,7 @@
#include <linux/poll.h>
#include <linux/ns_common.h>
#include <linux/fs_pin.h>
+#include <linux/watch_queue.h>
struct mnt_namespace {
atomic_t count;
@@ -67,9 +68,13 @@ struct mount {
int mnt_id; /* mount identifier */
int mnt_group_id; /* peer group identifier */
int mnt_expiry_mark; /* true if marked for expiry */
+ int mnt_nr_watchers; /* The number of subtree watches tracking this */
struct hlist_head mnt_pins;
struct fs_pin mnt_umount;
struct dentry *mnt_ex_mountpoint;
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+ struct watch_list *mnt_watchers; /* Watches on dentries within this mount */
+#endif
atomic_t mnt_notify_counter; /* Number of notifications generated */
} __randomize_layout;
@@ -153,18 +158,8 @@ static inline bool is_anon_ns(struct mnt_namespace *ns)
return ns->seq == 0;
}
-/*
- * Type of mount topology change notification.
- */
-enum mount_notification_subtype {
- NOTIFY_MOUNT_NEW_MOUNT = 0, /* New mount added */
- NOTIFY_MOUNT_UNMOUNT = 1, /* Mount removed manually */
- NOTIFY_MOUNT_EXPIRY = 2, /* Automount expired */
- NOTIFY_MOUNT_READONLY = 3, /* Mount R/O state changed */
- NOTIFY_MOUNT_SETATTR = 4, /* Mount attributes changed */
- NOTIFY_MOUNT_MOVE_FROM = 5, /* Mount moved from here */
- NOTIFY_MOUNT_MOVE_TO = 6, /* Mount moved to here (compare op_id) */
-};
+extern void post_mount_notification(struct mount *changed,
+ struct mount_notification *notify);
static inline void notify_mount(struct mount *changed,
struct mount *aux,
@@ -172,4 +167,18 @@ static inline void notify_mount(struct mount *changed,
u32 info_flags)
{
atomic_inc(&changed->mnt_notify_counter);
+
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+ {
+ struct mount_notification n = {
+ .watch.type = WATCH_TYPE_MOUNT_NOTIFY,
+ .watch.subtype = subtype,
+ .watch.info = info_flags | sizeof(n),
+ .triggered_on = changed->mnt_id,
+ .changed_mount = aux ? aux->mnt_id : 0,
+ };
+
+ post_mount_notification(changed, &n);
+ }
+#endif
}
new file mode 100644
@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Provide mount topology/attribute change notifications.
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/syscalls.h>
+#include <linux/slab.h>
+#include <linux/security.h>
+#include "mount.h"
+
+/*
+ * Post mount notifications to all watches going rootwards along the tree.
+ *
+ * Must be called with the mount_lock held.
+ */
+void post_mount_notification(struct mount *changed,
+ struct mount_notification *notify)
+{
+ const struct cred *cred = current_cred();
+ struct path cursor;
+ struct mount *mnt;
+ unsigned seq;
+
+ seq = 0;
+ rcu_read_lock();
+restart:
+ cursor.mnt = &changed->mnt;
+ cursor.dentry = changed->mnt.mnt_root;
+ mnt = real_mount(cursor.mnt);
+ notify->watch.info &= ~WATCH_INFO_IN_SUBTREE;
+
+ read_seqbegin_or_lock(&rename_lock, &seq);
+ for (;;) {
+ if (mnt->mnt_watchers &&
+ !hlist_empty(&mnt->mnt_watchers->watchers)) {
+ if (cursor.dentry->d_flags & DCACHE_MOUNT_WATCH)
+ post_watch_notification(mnt->mnt_watchers,
+ ¬ify->watch, cred,
+ (unsigned long)cursor.dentry);
+ } else {
+ cursor.dentry = mnt->mnt.mnt_root;
+ }
+ notify->watch.info |= WATCH_INFO_IN_SUBTREE;
+
+ if (cursor.dentry == cursor.mnt->mnt_root ||
+ IS_ROOT(cursor.dentry)) {
+ struct mount *parent = READ_ONCE(mnt->mnt_parent);
+
+ /* Escaped? */
+ if (cursor.dentry != cursor.mnt->mnt_root)
+ break;
+
+ /* Global root? */
+ if (mnt == parent)
+ break;
+
+ cursor.dentry = READ_ONCE(mnt->mnt_mountpoint);
+ mnt = parent;
+ cursor.mnt = &mnt->mnt;
+ } else {
+ cursor.dentry = cursor.dentry->d_parent;
+ }
+ }
+
+ if (need_seqretry(&rename_lock, seq)) {
+ seq = 1;
+ goto restart;
+ }
+
+ done_seqretry(&rename_lock, seq);
+ rcu_read_unlock();
+}
+
+static void release_mount_watch(struct watch *watch)
+{
+ struct vfsmount *mnt = watch->private;
+ struct dentry *dentry = (struct dentry *)(unsigned long)watch->id;
+
+ dput(dentry);
+ mntput(mnt);
+}
+
+/**
+ * sys_watch_mount - Watch for mount topology/attribute changes
+ * @dfd: Base directory to pathwalk from or fd referring to mount.
+ * @filename: Path to mount to place the watch upon
+ * @at_flags: Pathwalk control flags
+ * @watch_fd: The watch queue to send notifications to.
+ * @watch_id: The watch ID to be placed in the notification (-1 to remove watch)
+ */
+SYSCALL_DEFINE5(watch_mount,
+ int, dfd,
+ const char __user *, filename,
+ unsigned int, at_flags,
+ int, watch_fd,
+ int, watch_id)
+{
+ struct watch_queue *wqueue;
+ struct watch_list *wlist = NULL;
+ struct watch *watch;
+ struct mount *m;
+ struct path path;
+ unsigned int lookup_flags =
+ LOOKUP_DIRECTORY | LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
+ int ret;
+
+ if (watch_id < -1 || watch_id > 0xff)
+ return -EINVAL;
+ if ((at_flags & ~(AT_NO_AUTOMOUNT | AT_EMPTY_PATH)) != 0)
+ return -EINVAL;
+ if (at_flags & AT_NO_AUTOMOUNT)
+ lookup_flags &= ~LOOKUP_AUTOMOUNT;
+ if (at_flags & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+
+ ret = user_path_at(dfd, filename, lookup_flags, &path);
+ if (ret)
+ return ret;
+
+ wqueue = get_watch_queue(watch_fd);
+ if (IS_ERR(wqueue))
+ goto err_path;
+
+ m = real_mount(path.mnt);
+
+ if (watch_id >= 0) {
+ ret = -ENOMEM;
+ if (!m->mnt_watchers) {
+ wlist = kzalloc(sizeof(*wlist), GFP_KERNEL);
+ if (!wlist)
+ goto err_wqueue;
+ init_watch_list(wlist, release_mount_watch);
+ }
+
+ watch = kzalloc(sizeof(*watch), GFP_KERNEL);
+ if (!watch)
+ goto err_wlist;
+
+ init_watch(watch, wqueue);
+ watch->id = (unsigned long)path.dentry;
+ watch->private = path.mnt;
+ watch->info_id = (u32)watch_id << 24;
+
+ ret = security_watch_mount(watch, &path);
+ if (ret < 0)
+ goto err_watch;
+
+ down_write(&m->mnt.mnt_sb->s_umount);
+ if (!m->mnt_watchers) {
+ m->mnt_watchers = wlist;
+ wlist = NULL;
+ }
+
+ ret = add_watch_to_object(watch, m->mnt_watchers);
+ if (ret == 0) {
+ spin_lock(&path.dentry->d_lock);
+ path.dentry->d_flags |= DCACHE_MOUNT_WATCH;
+ spin_unlock(&path.dentry->d_lock);
+ path_get(&path);
+ watch = NULL;
+ }
+ up_write(&m->mnt.mnt_sb->s_umount);
+ } else {
+ ret = -EBADSLT;
+ if (m->mnt_watchers) {
+ down_write(&m->mnt.mnt_sb->s_umount);
+ ret = remove_watch_from_object(m->mnt_watchers, wqueue,
+ (unsigned long)path.dentry,
+ false);
+ up_write(&m->mnt.mnt_sb->s_umount);
+ }
+ }
+
+err_watch:
+ kfree(watch);
+err_wlist:
+ kfree(wlist);
+err_wqueue:
+ put_watch_queue(wqueue);
+err_path:
+ path_put(&path);
+ return ret;
+}
@@ -515,7 +515,8 @@ static int mnt_make_readonly(struct mount *mnt)
mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
unlock_mount_hash();
if (ret == 0)
- notify_mount(mnt, NULL, NOTIFY_MOUNT_READONLY, 0x10000);
+ notify_mount(mnt, NULL, NOTIFY_MOUNT_READONLY,
+ WATCH_INFO_FLAG_0);
return ret;
}
@@ -1478,6 +1479,10 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
list_del_init(&p->mnt_expire);
list_del_init(&p->mnt_list);
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+ if (p->mnt_watchers)
+ remove_watch_list(p->mnt_watchers);
+#endif
ns = p->mnt_ns;
if (ns) {
ns->mounts--;
@@ -2115,7 +2120,7 @@ static int attach_recursive_mnt(struct mount *source_mnt,
mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
notify_mount(dest_mnt, source_mnt, NOTIFY_MOUNT_NEW_MOUNT,
source_mnt->mnt.mnt_sb->s_flags & SB_SUBMOUNT ?
- 0x10000 : 0);
+ WATCH_INFO_FLAG_0 : 0);
commit_tree(source_mnt);
}
@@ -217,6 +217,7 @@ struct dentry_operations {
#define DCACHE_PAR_LOOKUP 0x10000000 /* being looked up (with parent locked shared) */
#define DCACHE_DENTRY_CURSOR 0x20000000
#define DCACHE_NORCU 0x40000000 /* No RCU delay for freeing */
+#define DCACHE_MOUNT_WATCH 0x80000000 /* There's a mount watch here */
extern seqlock_t rename_lock;
@@ -1001,6 +1001,8 @@ asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
asmlinkage long sys_fsinfo(int dfd, const char __user *path,
struct fsinfo_params __user *params,
void __user *buffer, size_t buf_size);
+asmlinkage long sys_watch_mount(int dfd, const char __user *path,
+ unsigned int at_flags, int watch_fd, int watch_id);
/*
* Architecture-specific system calls
@@ -105,4 +105,28 @@ struct key_notification {
__u32 aux; /* Per-type auxiliary data */
};
+/*
+ * Type of mount topology change notification.
+ */
+enum mount_notification_subtype {
+ NOTIFY_MOUNT_NEW_MOUNT = 0, /* New mount added */
+ NOTIFY_MOUNT_UNMOUNT = 1, /* Mount removed manually */
+ NOTIFY_MOUNT_EXPIRY = 2, /* Automount expired */
+ NOTIFY_MOUNT_READONLY = 3, /* Mount R/O state changed */
+ NOTIFY_MOUNT_SETATTR = 4, /* Mount attributes changed */
+ NOTIFY_MOUNT_MOVE_FROM = 5, /* Mount moved from here */
+ NOTIFY_MOUNT_MOVE_TO = 6, /* Mount moved to here (compare op_id) */
+};
+
+/*
+ * Mount topology/configuration change notification record.
+ * - watch.type = WATCH_TYPE_MOUNT_NOTIFY
+ * - watch.subtype = enum mount_notification_subtype
+ */
+struct mount_notification {
+ struct watch_notification watch; /* WATCH_TYPE_MOUNT_NOTIFY */
+ __u32 triggered_on; /* The mount that the notify was on */
+ __u32 changed_mount; /* The mount that got changed */
+};
+
#endif /* _UAPI_LINUX_WATCH_QUEUE_H */
@@ -88,6 +88,9 @@ COND_SYSCALL(ioprio_get);
/* fs/locks.c */
COND_SYSCALL(flock);
+/* fs/mount_notify.c */
+COND_SYSCALL(mount_notify);
+
/* fs/namei.c */
/* fs/namespace.c */
Add a mount notification facility whereby notifications about changes in mount topology and configuration can be received. Note that this only covers vfsmount topology changes and not superblock events. A separate facility will be added for that. Firstly, an event queue needs to be created: fd = open("/dev/event_queue", O_RDWR); ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n); then a notification can be set up to report notifications via that queue: struct watch_notification_filter filter = { .nr_filters = 1, .filters = { [0] = { .type = WATCH_TYPE_MOUNT_NOTIFY, .subtype_filter[0] = UINT_MAX, }, }, }; ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter); watch_mount(AT_FDCWD, "/", 0, fd, 0x02); In this case, it would let me monitor the mount topology subtree rooted at "/" for events. Mount notifications propagate up the tree towards the root, so a watch will catch all of the events happening in the subtree rooted at the watch. After setting the watch, records will be placed into the queue when, for example, as superblock switches between read-write and read-only. Records are of the following format: struct mount_notification { struct watch_notification watch; __u32 triggered_on; __u32 changed_mount; } *n; Where: n->watch.type will be WATCH_TYPE_MOUNT_NOTIFY. n->watch.subtype will indicate the type of event, such as NOTIFY_MOUNT_NEW_MOUNT. n->watch.info & WATCH_INFO_LENGTH will indicate the length of the record. n->watch.info & WATCH_INFO_ID will be the fifth argument to watch_mount(), shifted. n->watch.info & WATCH_INFO_FLAG_0 will be used for NOTIFY_MOUNT_READONLY, being set if the superblock becomes R/O, and being cleared otherwise, and for NOTIFY_MOUNT_NEW_MOUNT, being set if the new mount is a submount (e.g. an automount). n->triggered_on indicates the ID of the mount on which the watch was installed. n->changed_mount indicates the ID of the mount that was affected. The mount IDs can be retrieved with the fsinfo() syscall, using the fsinfo_mount_info and fsinfo_mount_child attributes. There are notification counters there too for when a buffer overrun occurs, thereby allowing the mount tree to be quickly rescanned. Note that it is permissible for event records to be of variable length - or, at least, the length may be dependent on the subtype. Note also that the queue can be shared between multiple notifications of various types. Signed-off-by: David Howells <dhowells@redhat.com> --- arch/x86/entry/syscalls/syscall_32.tbl | 1 arch/x86/entry/syscalls/syscall_64.tbl | 1 fs/Kconfig | 9 ++ fs/Makefile | 1 fs/mount.h | 33 ++++-- fs/mount_notify.c | 187 ++++++++++++++++++++++++++++++++ fs/namespace.c | 9 +- include/linux/dcache.h | 1 include/linux/syscalls.h | 2 include/uapi/linux/watch_queue.h | 24 ++++ kernel/sys_ni.c | 3 + 11 files changed, 257 insertions(+), 14 deletions(-) create mode 100644 fs/mount_notify.c