linux-brain/fs/proc_namespace.c

// SPDX-License-Identifier: GPL-2.0
/*
 * fs/proc_namespace.c - handling of /proc/<pid>/{mounts,mountinfo,mountstats}
 *
 * In fact, that's a piece of procfs; it's *almost* isolated from
 * the rest of fs/proc, but has rather close relationships with
 * fs/namespace.c, thus here instead of fs/proc
 *
 */
#include <linux/mnt_namespace.h>
#include <linux/nsproxy.h>
#include <linux/security.h>
#include <linux/fs_struct.h>
#include <linux/sched/task.h>

#include "proc/internal.h" /* only for get_proc_task() in ->open() */

#include "pnode.h"
#include "internal.h"

static __poll_t mounts_poll(struct file *file, poll_table *wait)
{
	struct seq_file *m = file->private_data;
	struct proc_mounts *p = m->private;
	struct mnt_namespace *ns = p->ns;
	__poll_t res = EPOLLIN | EPOLLRDNORM;
	int event;

	poll_wait(file, &p->ns->poll, wait);

	event = READ_ONCE(ns->event);
	if (m->poll_event != event) {
		m->poll_event = event;
		res |= EPOLLERR | EPOLLPRI;
	}

	return res;
}

struct proc_fs_info {
	int flag;
	const char *str;
};

static int show_sb_opts(struct seq_file *m, struct super_block *sb)
{
	static const struct proc_fs_info fs_info[] = {
		{ SB_SYNCHRONOUS, ",sync" },
		{ SB_DIRSYNC, ",dirsync" },
		{ SB_MANDLOCK, ",mand" },
		{ SB_LAZYTIME, ",lazytime" },
		{ 0, NULL }
	};
	const struct proc_fs_info *fs_infop;

	for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
		if (sb->s_flags & fs_infop->flag)
			seq_puts(m, fs_infop->str);
	}

	return security_sb_show_options(m, sb);
}

static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
{
	static const struct proc_fs_info mnt_info[] = {
		{ MNT_NOSUID, ",nosuid" },
		{ MNT_NODEV, ",nodev" },
		{ MNT_NOEXEC, ",noexec" },
		{ MNT_NOATIME, ",noatime" },
		{ MNT_NODIRATIME, ",nodiratime" },
		{ MNT_RELATIME, ",relatime" },
		{ 0, NULL }
	};
	const struct proc_fs_info *fs_infop;

	for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
		if (mnt->mnt_flags & fs_infop->flag)
			seq_puts(m, fs_infop->str);
	}
}

static inline void mangle(struct seq_file *m, const char *s)
{
	seq_escape(m, s, " \t\n\\");
}

static void show_type(struct seq_file *m, struct super_block *sb)
{
	mangle(m, sb->s_type->name);
	if (sb->s_subtype && sb->s_subtype[0]) {
		seq_putc(m, '.');
		mangle(m, sb->s_subtype);
	}
}

static int show_vfsmnt(struct seq_file *m, struct vfsmount *mnt)
{
	struct proc_mounts *p = m->private;
	struct mount *r = real_mount(mnt);
	struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
	struct super_block *sb = mnt_path.dentry->d_sb;
	int err;

	if (sb->s_op->show_devname) {
		err = sb->s_op->show_devname(m, mnt_path.dentry);
		if (err)
			goto out;
	} else {
		mangle(m, r->mnt_devname ? r->mnt_devname : "none");
	}
	seq_putc(m, ' ');
	/* mountpoints outside of chroot jail will give SEQ_SKIP on this */
	err = seq_path_root(m, &mnt_path, &p->root, " \t\n\\");
	if (err)
		goto out;
	seq_putc(m, ' ');
	show_type(m, sb);
	seq_puts(m, __mnt_is_readonly(mnt) ? " ro" : " rw");
	err = show_sb_opts(m, sb);
	if (err)
		goto out;
	show_mnt_opts(m, mnt);
	if (sb->s_op->show_options)
		err = sb->s_op->show_options(m, mnt_path.dentry);
	seq_puts(m, " 0 0\n");
out:
	return err;
}

static int show_mountinfo(struct seq_file *m, struct vfsmount *mnt)
{
	struct proc_mounts *p = m->private;
	struct mount *r = real_mount(mnt);
	struct super_block *sb = mnt->mnt_sb;
	struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
	int err;

	seq_printf(m, "%i %i %u:%u ", r->mnt_id, r->mnt_parent->mnt_id,
		   MAJOR(sb->s_dev), MINOR(sb->s_dev));
	if (sb->s_op->show_path) {
		err = sb->s_op->show_path(m, mnt->mnt_root);
		if (err)
			goto out;
	} else {
		seq_dentry(m, mnt->mnt_root, " \t\n\\");
	}
	seq_putc(m, ' ');

	/* mountpoints outside of chroot jail will give SEQ_SKIP on this */
	err = seq_path_root(m, &mnt_path, &p->root, " \t\n\\");
	if (err)
		goto out;

	seq_puts(m, mnt->mnt_flags & MNT_READONLY ? " ro" : " rw");
	show_mnt_opts(m, mnt);

	/* Tagged fields ("foo:X" or "bar") */
	if (IS_MNT_SHARED(r))
		seq_printf(m, " shared:%i", r->mnt_group_id);
	if (IS_MNT_SLAVE(r)) {
		int master = r->mnt_master->mnt_group_id;
		int dom = get_dominating_id(r, &p->root);
		seq_printf(m, " master:%i", master);
		if (dom && dom != master)
			seq_printf(m, " propagate_from:%i", dom);
	}
	if (IS_MNT_UNBINDABLE(r))
		seq_puts(m, " unbindable");

	/* Filesystem specific data */
	seq_puts(m, " - ");
	show_type(m, sb);
	seq_putc(m, ' ');
	if (sb->s_op->show_devname) {
		err = sb->s_op->show_devname(m, mnt->mnt_root);
		if (err)
			goto out;
	} else {
		mangle(m, r->mnt_devname ? r->mnt_devname : "none");
	}
	seq_puts(m, sb_rdonly(sb) ? " ro" : " rw");
	err = show_sb_opts(m, sb);
	if (err)
		goto out;
	if (sb->s_op->show_options)
		err = sb->s_op->show_options(m, mnt->mnt_root);
	seq_putc(m, '\n');
out:
	return err;
}

static int show_vfsstat(struct seq_file *m, struct vfsmount *mnt)
{
	struct proc_mounts *p = m->private;
	struct mount *r = real_mount(mnt);
	struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
	struct super_block *sb = mnt_path.dentry->d_sb;
	int err;

	/* device */
	if (sb->s_op->show_devname) {
		seq_puts(m, "device ");
		err = sb->s_op->show_devname(m, mnt_path.dentry);
		if (err)
			goto out;
	} else {
		if (r->mnt_devname) {
			seq_puts(m, "device ");
			mangle(m, r->mnt_devname);
		} else
			seq_puts(m, "no device");
	}

	/* mount point */
	seq_puts(m, " mounted on ");
	/* mountpoints outside of chroot jail will give SEQ_SKIP on this */
	err = seq_path_root(m, &mnt_path, &p->root, " \t\n\\");
	if (err)
		goto out;
	seq_putc(m, ' ');

	/* file system type */
	seq_puts(m, "with fstype ");
	show_type(m, sb);

	/* optional statistics */
	if (sb->s_op->show_stats) {
		seq_putc(m, ' ');
		err = sb->s_op->show_stats(m, mnt_path.dentry);
	}

	seq_putc(m, '\n');
out:
	return err;
}

static int mounts_open_common(struct inode *inode, struct file *file,
			      int (*show)(struct seq_file *, struct vfsmount *))
{
	struct task_struct *task = get_proc_task(inode);
	struct nsproxy *nsp;
	struct mnt_namespace *ns = NULL;
	struct path root;
	struct proc_mounts *p;
	struct seq_file *m;
	int ret = -EINVAL;

	if (!task)
		goto err;

	task_lock(task);
	nsp = task->nsproxy;
	if (!nsp || !nsp->mnt_ns) {
		task_unlock(task);
		put_task_struct(task);
		goto err;
	}
	ns = nsp->mnt_ns;
	get_mnt_ns(ns);
	if (!task->fs) {
		task_unlock(task);
		put_task_struct(task);
		ret = -ENOENT;
		goto err_put_ns;
	}
	get_fs_root(task->fs, &root);
	task_unlock(task);
	put_task_struct(task);

	ret = seq_open_private(file, &mounts_op, sizeof(struct proc_mounts));
	if (ret)
		goto err_put_path;

	m = file->private_data;
	m->poll_event = ns->event;

	p = m->private;
	p->ns = ns;
	p->root = root;
	p->show = show;
	p->cached_event = ~0ULL;

	return 0;

 err_put_path:
	path_put(&root);
 err_put_ns:
	put_mnt_ns(ns);
 err:
	return ret;
}

static int mounts_release(struct inode *inode, struct file *file)
{
	struct seq_file *m = file->private_data;
	struct proc_mounts *p = m->private;
	path_put(&p->root);
	put_mnt_ns(p->ns);
	return seq_release_private(inode, file);
}

static int mounts_open(struct inode *inode, struct file *file)
{
	return mounts_open_common(inode, file, show_vfsmnt);
}

static int mountinfo_open(struct inode *inode, struct file *file)
{
	return mounts_open_common(inode, file, show_mountinfo);
}

static int mountstats_open(struct inode *inode, struct file *file)
{
	return mounts_open_common(inode, file, show_vfsstat);
}

const struct file_operations proc_mounts_operations = {
	.open		= mounts_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= mounts_release,
	.poll		= mounts_poll,
};

const struct file_operations proc_mountinfo_operations = {
	.open		= mountinfo_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= mounts_release,
	.poll		= mounts_poll,
};

const struct file_operations proc_mountstats_operations = {
	.open		= mountstats_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= mounts_release,
};