Re: [PATCH 10/25] vfs: Allow mount information to be queried by fsinfo() [ver #14]
From: Christian Brauner
Date: Wed Jun 26 2019 - 05:53:57 EST
On Mon, Jun 24, 2019 at 03:10:20PM +0100, David Howells wrote:
> Allow mount information, including information about the topology tree to
> be queried with the fsinfo() system call. Usage of AT_FSINFO_MOUNTID_PATH
> allows overlapping mounts to be queried.
Again, I really think that this doesn't need to land at the same time as
the basic infrastructure for fsinfo()...
>
> To this end, four fsinfo() attributes are provided:
>
> (1) FSINFO_ATTR_MOUNT_INFO.
>
> This is a structure providing information about a mount, including:
>
> - Mounted superblock ID.
> - Mount ID (as AT_FSINFO_MOUNTID_PATH).
> - Parent mount ID.
> - Mount attributes (eg. R/O, NOEXEC).
> - Number of change notifications generated.
>
> Note that the parent mount ID is overridden to the ID of the queried
> mount if the parent lies outside of the chroot or dfd tree.
>
> (2) FSINFO_ATTR_MOUNT_DEVNAME.
>
> This a string providing the device name associated with the mount.
>
> Note that the device name may be a path that lies outside of the root.
>
> (3) FSINFO_ATTR_MOUNT_CHILDREN.
>
> This produces an array of structures, one for each child and capped
> with one for the argument mount (checked after listing all the
> children). Each element contains the mount ID and the notification
> counter of the respective mount object.
>
> (4) FSINFO_ATTR_MOUNT_SUBMOUNT.
>
> This is a 1D array of strings, indexed with struct fsinfo_params::Nth.
> Each string is the relative pathname of the corresponding child
> returned by FSINFO_ATTR_MOUNT_CHILDREN.
>
> Note that paths in the mount at the base of the tree (whether that be
> dfd or chroot) are relative to the base of the tree, not the root
> directory of that mount.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> ---
>
> fs/d_path.c | 2
> fs/fsinfo.c | 8 ++
> fs/internal.h | 9 ++
> fs/namespace.c | 177 +++++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/fsinfo.h | 28 +++++++
> samples/vfs/test-fsinfo.c | 47 +++++++++++
> 6 files changed, 267 insertions(+), 4 deletions(-)
>
> diff --git a/fs/d_path.c b/fs/d_path.c
> index a7d0a96b35ce..89d77c264c5f 100644
> --- a/fs/d_path.c
> +++ b/fs/d_path.c
> @@ -227,7 +227,7 @@ static int prepend_unreachable(char **buffer, int *buflen)
> return prepend(buffer, buflen, "(unreachable)", 13);
> }
>
> -static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
> +void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
> {
> unsigned seq;
>
> diff --git a/fs/fsinfo.c b/fs/fsinfo.c
> index 3b218f9fedb7..61f00f375fd2 100644
> --- a/fs/fsinfo.c
> +++ b/fs/fsinfo.c
> @@ -348,6 +348,10 @@ int generic_fsinfo(struct path *path, struct fsinfo_kparams *params)
> case _genf(PARAM_SPECIFICATION, param_specification);
> case _genf(PARAM_ENUM, param_enum);
> case _genp(PARAMETERS, parameters);
> + case _genp(MOUNT_INFO, mount_info);
> + case _genp(MOUNT_DEVNAME, mount_devname);
> + case _genp(MOUNT_CHILDREN, mount_children);
> + case _genp(MOUNT_SUBMOUNT, mount_submount);
> default:
> return -EOPNOTSUPP;
> }
> @@ -627,6 +631,10 @@ static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
> FSINFO_STRUCT_N (PARAM_ENUM, param_enum),
> FSINFO_OPAQUE (PARAMETERS, -),
> FSINFO_OPAQUE (LSM_PARAMETERS, -),
> + FSINFO_STRUCT (MOUNT_INFO, mount_info),
> + FSINFO_STRING (MOUNT_DEVNAME, mount_devname),
> + FSINFO_STRUCT_ARRAY (MOUNT_CHILDREN, mount_child),
> + FSINFO_STRING_N (MOUNT_SUBMOUNT, mount_submount),
> };
>
> /**
> diff --git a/fs/internal.h b/fs/internal.h
> index 074b1c65e3bd..bb3d8efa7f49 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -53,6 +53,11 @@ void __generic_write_end(struct inode *inode, loff_t pos, unsigned copied,
> */
> extern void __init chrdev_init(void);
>
> +/*
> + * d_path.c
> + */
> +extern void get_fs_root_rcu(struct fs_struct *fs, struct path *root);
> +
> /*
> * fs_context.c
> */
> @@ -98,6 +103,10 @@ extern void __mnt_drop_write_file(struct file *);
>
> extern void dissolve_on_fput(struct vfsmount *);
> extern int lookup_mount_object(struct path *, int, struct path *);
> +extern int fsinfo_generic_mount_info(struct path *, struct fsinfo_kparams *);
> +extern int fsinfo_generic_mount_devname(struct path *, struct fsinfo_kparams *);
> +extern int fsinfo_generic_mount_children(struct path *, struct fsinfo_kparams *);
> +extern int fsinfo_generic_mount_submount(struct path *, struct fsinfo_kparams *);
>
> /*
> * fs_struct.c
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 1450faab96b9..2ec7d9d1905a 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -29,6 +29,7 @@
> #include <linux/sched/task.h>
> #include <uapi/linux/mount.h>
> #include <linux/fs_context.h>
> +#include <linux/fsinfo.h>
>
> #include "pnode.h"
> #include "internal.h"
> @@ -4112,3 +4113,179 @@ int lookup_mount_object(struct path *root, int mnt_id, struct path *_mntpt)
> unlock_mount_hash();
> goto out_unlock;
> }
> +
> +#ifdef CONFIG_FSINFO
> +int fsinfo_generic_mount_info(struct path *path, struct fsinfo_kparams *params)
> +{
> + struct fsinfo_mount_info *p = params->buffer;
> + struct super_block *sb;
> + struct mount *m;
> + struct path root;
> + unsigned int flags;
> +
> + if (!path->mnt)
> + return -ENODATA;
> +
> + m = real_mount(path->mnt);
> + sb = m->mnt.mnt_sb;
> +
> + p->f_sb_id = sb->s_unique_id;
> + p->mnt_id = m->mnt_id;
> + p->parent_id = m->mnt_parent->mnt_id;
> + p->notify_counter = atomic_read(&m->mnt_notify_counter);
> +
> + get_fs_root(current->fs, &root);
> + if (path->mnt == root.mnt) {
> + p->parent_id = p->mnt_id;
> + } else {
> + rcu_read_lock();
> + if (!are_paths_connected(&root, path))
> + p->parent_id = p->mnt_id;
> + rcu_read_unlock();
> + }
> + if (IS_MNT_SHARED(m))
> + p->group_id = m->mnt_group_id;
> + if (IS_MNT_SLAVE(m)) {
> + int master = m->mnt_master->mnt_group_id;
> + int dom = get_dominating_id(m, &root);
> + p->master_id = master;
> + if (dom && dom != master)
> + p->from_id = dom;
> + }
> + path_put(&root);
> +
> + flags = READ_ONCE(m->mnt.mnt_flags);
> + if (flags & MNT_READONLY)
> + p->attr |= MOUNT_ATTR_RDONLY;
> + if (flags & MNT_NOSUID)
> + p->attr |= MOUNT_ATTR_NOSUID;
> + if (flags & MNT_NODEV)
> + p->attr |= MOUNT_ATTR_NODEV;
> + if (flags & MNT_NOEXEC)
> + p->attr |= MOUNT_ATTR_NOEXEC;
> + if (flags & MNT_NODIRATIME)
> + p->attr |= MOUNT_ATTR_NODIRATIME;
> +
> + if (flags & MNT_NOATIME)
> + p->attr |= MOUNT_ATTR_NOATIME;
> + else if (flags & MNT_RELATIME)
> + p->attr |= MOUNT_ATTR_RELATIME;
> + else
> + p->attr |= MOUNT_ATTR_STRICTATIME;
> + return sizeof(*p);
> +}
> +
> +int fsinfo_generic_mount_devname(struct path *path, struct fsinfo_kparams *params)
> +{
> + struct mount *m;
> + size_t len;
> +
> + if (!path->mnt)
> + return -ENODATA;
> +
> + m = real_mount(path->mnt);
> + len = strlen(m->mnt_devname);
> + memcpy(params->buffer, m->mnt_devname, len);
> + return len;
> +}
> +
> +/*
> + * Store a mount record into the fsinfo buffer.
> + */
> +static void store_mount_fsinfo(struct fsinfo_kparams *params,
> + struct fsinfo_mount_child *child)
> +{
> + unsigned int usage = params->usage;
> + unsigned int total = sizeof(*child);
> +
> + if (params->usage >= INT_MAX)
> + return;
> + params->usage = usage + total;
> + if (params->buffer && params->usage <= params->buf_size)
> + memcpy(params->buffer + usage, child, total);
> +}
> +
> +/*
> + * Return information about the submounts relative to path.
> + */
> +int fsinfo_generic_mount_children(struct path *path, struct fsinfo_kparams *params)
> +{
> + struct fsinfo_mount_child record;
> + struct mount *m, *child;
> +
> + if (!path->mnt)
> + return -ENODATA;
> +
> + m = real_mount(path->mnt);
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(child, &m->mnt_mounts, mnt_child) {
> + if (child->mnt_parent != m)
> + continue;
> + record.mnt_id = child->mnt_id;
> + record.notify_counter = atomic_read(&child->mnt_notify_counter);
> + store_mount_fsinfo(params, &record);
> + }
> + rcu_read_unlock();
> +
> + /* End the list with a copy of the parameter mount's details so that
> + * userspace can quickly check for changes.
> + */
> + record.mnt_id = m->mnt_id;
> + record.notify_counter = atomic_read(&m->mnt_notify_counter);
> + store_mount_fsinfo(params, &record);
> + return params->usage;
> +}
> +
> +/*
> + * Return the path of the Nth submount relative to path. This is derived from
> + * d_path(), but the root determination is more complicated.
> + */
> +int fsinfo_generic_mount_submount(struct path *path, struct fsinfo_kparams *params)
> +{
> + struct mountpoint *mp;
> + struct mount *m, *child;
> + struct path mountpoint, root;
> + unsigned int n = params->Nth;
> + size_t len;
> + void *p;
> +
> + if (!path->mnt)
> + return -ENODATA;
> +
> + rcu_read_lock();
> +
> + m = real_mount(path->mnt);
> + list_for_each_entry_rcu(child, &m->mnt_mounts, mnt_child) {
> + mp = READ_ONCE(child->mnt_mp);
> + if (child->mnt_parent != m || !mp)
> + continue;
> + if (n-- == 0)
> + goto found;
> + }
> + rcu_read_unlock();
> + return -ENODATA;
> +
> +found:
> + mountpoint.mnt = path->mnt;
> + mountpoint.dentry = READ_ONCE(mp->m_dentry);
> +
> + get_fs_root_rcu(current->fs, &root);
> + if (root.mnt != path->mnt) {
> + root.mnt = path->mnt;
> + root.dentry = path->mnt->mnt_root;
> + }
> +
> + p = __d_path(&mountpoint, &root, params->buffer, params->buf_size);
> + rcu_read_unlock();
> +
> + if (IS_ERR(p))
> + return PTR_ERR(p);
> + if (!p)
> + return -EPERM;
> +
> + len = (params->buffer + params->buf_size) - p;
> + memmove(params->buffer, p, len);
> + return len;
> +}
> +#endif /* CONFIG_FSINFO */
> diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
> index bae0bdc9ace9..88e1d004ac6c 100644
> --- a/include/uapi/linux/fsinfo.h
> +++ b/include/uapi/linux/fsinfo.h
> @@ -32,6 +32,10 @@ enum fsinfo_attribute {
> FSINFO_ATTR_PARAM_ENUM = 14, /* Nth enum-to-val */
> FSINFO_ATTR_PARAMETERS = 15, /* Mount parameters (large string) */
> FSINFO_ATTR_LSM_PARAMETERS = 16, /* LSM Mount parameters (large string) */
> + FSINFO_ATTR_MOUNT_INFO = 17, /* Mount object information */
> + FSINFO_ATTR_MOUNT_DEVNAME = 18, /* Mount object device name (string) */
> + FSINFO_ATTR_MOUNT_CHILDREN = 19, /* Submount list (array) */
> + FSINFO_ATTR_MOUNT_SUBMOUNT = 20, /* Relative path of Nth submount (string) */
> FSINFO_ATTR__NR
> };
>
> @@ -276,4 +280,28 @@ struct fsinfo_param_enum {
> char name[252]; /* Name of the enum value */
> };
>
> +/*
> + * Information struct for fsinfo(FSINFO_ATTR_MOUNT_INFO).
> + */
> +struct fsinfo_mount_info {
> + __u64 f_sb_id; /* Superblock ID */
> + __u32 mnt_id; /* Mount identifier (use with AT_FSINFO_MOUNTID_PATH) */
> + __u32 parent_id; /* Parent mount identifier */
> + __u32 group_id; /* Mount group ID */
> + __u32 master_id; /* Slave master group ID */
> + __u32 from_id; /* Slave propagated from ID */
> + __u32 attr; /* MOUNT_ATTR_* flags */
> + __u32 notify_counter; /* Number of notifications generated. */
> + __u32 __reserved[1];
> +};
> +
> +/*
> + * Information struct element for fsinfo(FSINFO_ATTR_MOUNT_CHILDREN).
> + * - An extra element is placed on the end representing the parent mount.
> + */
> +struct fsinfo_mount_child {
> + __u32 mnt_id; /* Mount identifier (use with AT_FSINFO_MOUNTID_PATH) */
> + __u32 notify_counter; /* Number of notifications generated on mount. */
> +};
> +
> #endif /* _UAPI_LINUX_FSINFO_H */
> diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c
> index fadc5e1384fc..ab32a15d4c5b 100644
> --- a/samples/vfs/test-fsinfo.c
> +++ b/samples/vfs/test-fsinfo.c
> @@ -21,10 +21,10 @@
> #include <errno.h>
> #include <time.h>
> #include <math.h>
> -#include <fcntl.h>
> #include <sys/syscall.h>
> #include <linux/fsinfo.h>
> #include <linux/socket.h>
> +#include <linux/fcntl.h>
> #include <sys/stat.h>
> #include <arpa/inet.h>
>
> @@ -83,6 +83,10 @@ static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
> FSINFO_STRUCT_N (PARAM_ENUM, param_enum),
> FSINFO_OVERLARGE (PARAMETERS, -),
> FSINFO_OVERLARGE (LSM_PARAMETERS, -),
> + FSINFO_STRUCT (MOUNT_INFO, mount_info),
> + FSINFO_STRING (MOUNT_DEVNAME, mount_devname),
> + FSINFO_STRUCT_ARRAY (MOUNT_CHILDREN, mount_child),
> + FSINFO_STRING_N (MOUNT_SUBMOUNT, mount_submount),
> };
>
> #define FSINFO_NAME(X,Y) [FSINFO_ATTR_##X] = #Y
> @@ -104,6 +108,10 @@ static const char *fsinfo_attr_names[FSINFO_ATTR__NR] = {
> FSINFO_NAME (PARAM_ENUM, param_enum),
> FSINFO_NAME (PARAMETERS, parameters),
> FSINFO_NAME (LSM_PARAMETERS, lsm_parameters),
> + FSINFO_NAME (MOUNT_INFO, mount_info),
> + FSINFO_NAME (MOUNT_DEVNAME, mount_devname),
> + FSINFO_NAME (MOUNT_CHILDREN, mount_children),
> + FSINFO_NAME (MOUNT_SUBMOUNT, mount_submount),
> };
>
> union reply {
> @@ -116,6 +124,8 @@ union reply {
> struct fsinfo_capabilities caps;
> struct fsinfo_timestamp_info timestamps;
> struct fsinfo_volume_uuid uuid;
> + struct fsinfo_mount_info mount_info;
> + struct fsinfo_mount_child mount_children[1];
> };
>
> static void dump_hex(unsigned int *data, int from, int to)
> @@ -319,6 +329,29 @@ static void dump_attr_VOLUME_UUID(union reply *r, int size)
> f->uuid[14], f->uuid[15]);
> }
>
> +static void dump_attr_MOUNT_INFO(union reply *r, int size)
> +{
> + struct fsinfo_mount_info *f = &r->mount_info;
> +
> + printf("\n");
> + printf("\tsb_id : %llx\n", (unsigned long long)f->f_sb_id);
> + printf("\tmnt_id : %x\n", f->mnt_id);
> + printf("\tparent : %x\n", f->parent_id);
> + printf("\tgroup : %x\n", f->group_id);
> + printf("\tattr : %x\n", f->attr);
> + printf("\tnotifs : %x\n", f->notify_counter);
> +}
> +
> +static void dump_attr_MOUNT_CHILDREN(union reply *r, int size)
> +{
> + struct fsinfo_mount_child *f = r->mount_children;
> + int i = 0;
> +
> + printf("\n");
> + for (; size >= sizeof(*f); size -= sizeof(*f), f++)
> + printf("\t[%u] %8x %8x\n", i++, f->mnt_id, f->notify_counter);
> +}
> +
> /*
> *
> */
> @@ -334,6 +367,8 @@ static const dumper_t fsinfo_attr_dumper[FSINFO_ATTR__NR] = {
> FSINFO_DUMPER(CAPABILITIES),
> FSINFO_DUMPER(TIMESTAMP_INFO),
> FSINFO_DUMPER(VOLUME_UUID),
> + FSINFO_DUMPER(MOUNT_INFO),
> + FSINFO_DUMPER(MOUNT_CHILDREN),
> };
>
> static void dump_fsinfo(enum fsinfo_attribute attr,
> @@ -536,16 +571,21 @@ int main(int argc, char **argv)
> unsigned int attr;
> int raw = 0, opt, Nth, Mth;
>
> - while ((opt = getopt(argc, argv, "adlr"))) {
> + while ((opt = getopt(argc, argv, "Madlr"))) {
> switch (opt) {
> + case 'M':
> + params.at_flags = AT_FSINFO_MOUNTID_PATH;
> + continue;
> case 'a':
> params.at_flags |= AT_NO_AUTOMOUNT;
> + params.at_flags &= ~AT_FSINFO_MOUNTID_PATH;
> continue;
> case 'd':
> debug = true;
> continue;
> case 'l':
> params.at_flags &= ~AT_SYMLINK_NOFOLLOW;
> + params.at_flags &= ~AT_FSINFO_MOUNTID_PATH;
> continue;
> case 'r':
> raw = 1;
> @@ -558,7 +598,8 @@ int main(int argc, char **argv)
> argv += optind;
>
> if (argc != 1) {
> - printf("Format: test-fsinfo [-alr] <file>\n");
> + printf("Format: test-fsinfo [-adlr] <file>\n");
> + printf("Format: test-fsinfo [-dr] -M <mnt_id>\n");
> exit(2);
> }
>
>