linux/fs/cifs/cifs_dfs_ref.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *   Contains the CIFS DFS referral mounting routines used for handling
 *   traversal via DFS junction point
 *
 *   Copyright (c) 2007 Igor Mammedov
 *   Copyright (C) International Business Machines  Corp., 2008
 *   Author(s): Igor Mammedov (niallain@gmail.com)
 *		Steve French (sfrench@us.ibm.com)
 */

#include <linux/dcache.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/slab.h>
#include <linux/vfs.h>
#include <linux/fs.h>
#include <linux/inet.h>
#include "cifsglob.h"
#include "cifsproto.h"
#include "cifsfs.h"
#include "dns_resolve.h"
#include "cifs_debug.h"
#include "dfs.h"
#include "fs_context.h"

static LIST_HEAD(cifs_dfs_automount_list);

static void cifs_dfs_expire_automounts(struct work_struct *work);
static DECLARE_DELAYED_WORK(cifs_dfs_automount_task,
			    cifs_dfs_expire_automounts);
static int cifs_dfs_mountpoint_expiry_timeout = 500 * HZ;

static void cifs_dfs_expire_automounts(struct work_struct *work)
{
	struct list_head *list = &cifs_dfs_automount_list;

	mark_mounts_for_expiry(list);
	if (!list_empty(list))
		schedule_delayed_work(&cifs_dfs_automount_task,
				      cifs_dfs_mountpoint_expiry_timeout);
}

void cifs_dfs_release_automount_timer(void)
{
	BUG_ON(!list_empty(&cifs_dfs_automount_list));
	cancel_delayed_work_sync(&cifs_dfs_automount_task);
}

/**
 * cifs_build_devname - build a devicename from a UNC and optional prepath
 * @nodename:	pointer to UNC string
 * @prepath:	pointer to prefixpath (or NULL if there isn't one)
 *
 * Build a new cifs devicename after chasing a DFS referral. Allocate a buffer
 * big enough to hold the final thing. Copy the UNC from the nodename, and
 * concatenate the prepath onto the end of it if there is one.
 *
 * Returns pointer to the built string, or a ERR_PTR. Caller is responsible
 * for freeing the returned string.
 */
char *
cifs_build_devname(char *nodename, const char *prepath)
{
	size_t pplen;
	size_t unclen;
	char *dev;
	char *pos;

	/* skip over any preceding delimiters */
	nodename += strspn(nodename, "\\");
	if (!*nodename)
		return ERR_PTR(-EINVAL);

	/* get length of UNC and set pos to last char */
	unclen = strlen(nodename);
	pos = nodename + unclen - 1;

	/* trim off any trailing delimiters */
	while (*pos == '\\') {
		--pos;
		--unclen;
	}

	/* allocate a buffer:
	 * +2 for preceding "//"
	 * +1 for delimiter between UNC and prepath
	 * +1 for trailing NULL
	 */
	pplen = prepath ? strlen(prepath) : 0;
	dev = kmalloc(2 + unclen + 1 + pplen + 1, GFP_KERNEL);
	if (!dev)
		return ERR_PTR(-ENOMEM);

	pos = dev;
	/* add the initial "//" */
	*pos = '/';
	++pos;
	*pos = '/';
	++pos;

	/* copy in the UNC portion from referral */
	memcpy(pos, nodename, unclen);
	pos += unclen;

	/* copy the prefixpath remainder (if there is one) */
	if (pplen) {
		*pos = '/';
		++pos;
		memcpy(pos, prepath, pplen);
		pos += pplen;
	}

	/* NULL terminator */
	*pos = '\0';

	convert_delimiter(dev, '/');
	return dev;
}

static int set_dest_addr(struct smb3_fs_context *ctx, const char *full_path)
{
	struct sockaddr *addr = (struct sockaddr *)&ctx->dstaddr;
	int rc;

	rc = dns_resolve_server_name_to_ip(full_path, addr, NULL);
	if (!rc)
		cifs_set_port(addr, ctx->port);
	return rc;
}

/*
 * Create a vfsmount that we can automount
 */
static struct vfsmount *cifs_dfs_do_automount(struct path *path)
{
	int rc;
	struct dentry *mntpt = path->dentry;
	struct fs_context *fc;
	struct cifs_sb_info *cifs_sb;
	void *page = NULL;
	struct smb3_fs_context *ctx, *cur_ctx;
	struct smb3_fs_context tmp;
	char *full_path;
	struct vfsmount *mnt;

	if (IS_ROOT(mntpt))
		return ERR_PTR(-ESTALE);

	/*
	 * The MSDFS spec states that paths in DFS referral requests and
	 * responses must be prefixed by a single '\' character instead of
	 * the double backslashes usually used in the UNC. This function
	 * gives us the latter, so we must adjust the result.
	 */
	cifs_sb = CIFS_SB(mntpt->d_sb);
	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS)
		return ERR_PTR(-EREMOTE);

	cur_ctx = cifs_sb->ctx;

	fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, mntpt);
	if (IS_ERR(fc))
		return ERR_CAST(fc);

	ctx = smb3_fc2context(fc);

	page = alloc_dentry_path();
	full_path = dfs_get_automount_devname(mntpt, page);
	if (IS_ERR(full_path)) {
		mnt = ERR_CAST(full_path);
		goto out;
	}
	cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);

	tmp = *cur_ctx;
	tmp.source = full_path;
	tmp.leaf_fullpath = NULL;
	tmp.UNC = tmp.prepath = NULL;
	tmp.dfs_root_ses = NULL;

	rc = smb3_fs_context_dup(ctx, &tmp);
	if (rc) {
		mnt = ERR_PTR(rc);
		goto out;
	}

	rc = set_dest_addr(ctx, full_path);
	if (rc) {
		mnt = ERR_PTR(rc);
		goto out;
	}

	rc = smb3_parse_devname(full_path, ctx);
	if (!rc)
		mnt = fc_mount(fc);
	else
		mnt = ERR_PTR(rc);

out:
	put_fs_context(fc);
	free_dentry_path(page);
	return mnt;
}

/*
 * Attempt to automount the referral
 */
struct vfsmount *cifs_dfs_d_automount(struct path *path)
{
	struct vfsmount *newmnt;

	cifs_dbg(FYI, "%s: %pd\n", __func__, path->dentry);

	newmnt = cifs_dfs_do_automount(path);
	if (IS_ERR(newmnt)) {
		cifs_dbg(FYI, "leaving %s [automount failed]\n" , __func__);
		return newmnt;
	}

	mntget(newmnt); /* prevent immediate expiration */
	mnt_set_expiry(newmnt, &cifs_dfs_automount_list);
	schedule_delayed_work(&cifs_dfs_automount_task,
			      cifs_dfs_mountpoint_expiry_timeout);
	cifs_dbg(FYI, "leaving %s [ok]\n" , __func__);
	return newmnt;
}

const struct inode_operations cifs_dfs_referral_inode_operations = {
};