linux/fs/cifs/dfs.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2022 Paulo Alcantara <palcantara@suse.de>
 */

#include <linux/namei.h>
#include "cifsproto.h"
#include "cifs_debug.h"
#include "dns_resolve.h"
#include "fs_context.h"
#include "dfs.h"

/**
 * dfs_parse_target_referral - set fs context for dfs target referral
 *
 * @full_path: full path in UNC format.
 * @ref: dfs referral pointer.
 * @ctx: smb3 fs context pointer.
 *
 * Return zero if dfs referral was parsed correctly, otherwise non-zero.
 */
int dfs_parse_target_referral(const char *full_path, const struct dfs_info3_param *ref,
			      struct smb3_fs_context *ctx)
{
	int rc;
	const char *prepath = NULL;
	char *path;

	if (!full_path || !*full_path || !ref || !ctx)
		return -EINVAL;

	if (WARN_ON_ONCE(!ref->node_name || ref->path_consumed < 0))
		return -EINVAL;

	if (strlen(full_path) - ref->path_consumed) {
		prepath = full_path + ref->path_consumed;
		/* skip initial delimiter */
		if (*prepath == '/' || *prepath == '\\')
			prepath++;
	}

	path = cifs_build_devname(ref->node_name, prepath);
	if (IS_ERR(path))
		return PTR_ERR(path);

	rc = smb3_parse_devname(path, ctx);
	if (rc)
		goto out;

	rc = dns_resolve_server_name_to_ip(path, (struct sockaddr *)&ctx->dstaddr, NULL);

out:
	kfree(path);
	return rc;
}

/*
 * cifs_build_path_to_root returns full path to root when we do not have an
 * existing connection (tcon)
 */
static char *build_unc_path_to_root(const struct smb3_fs_context *ctx,
				    const struct cifs_sb_info *cifs_sb, bool useppath)
{
	char *full_path, *pos;
	unsigned int pplen = useppath && ctx->prepath ? strlen(ctx->prepath) + 1 : 0;
	unsigned int unc_len = strnlen(ctx->UNC, MAX_TREE_SIZE + 1);

	if (unc_len > MAX_TREE_SIZE)
		return ERR_PTR(-EINVAL);

	full_path = kmalloc(unc_len + pplen + 1, GFP_KERNEL);
	if (full_path == NULL)
		return ERR_PTR(-ENOMEM);

	memcpy(full_path, ctx->UNC, unc_len);
	pos = full_path + unc_len;

	if (pplen) {
		*pos = CIFS_DIR_SEP(cifs_sb);
		memcpy(pos + 1, ctx->prepath, pplen);
		pos += pplen;
	}

	*pos = '\0'; /* add trailing null */
	convert_delimiter(full_path, CIFS_DIR_SEP(cifs_sb));
	cifs_dbg(FYI, "%s: full_path=%s\n", __func__, full_path);
	return full_path;
}

static int get_session(struct cifs_mount_ctx *mnt_ctx, const char *full_path)
{
	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
	int rc;

	ctx->leaf_fullpath = (char *)full_path;
	rc = cifs_mount_get_session(mnt_ctx);
	ctx->leaf_fullpath = NULL;
	if (!rc) {
		struct cifs_ses *ses = mnt_ctx->ses;

		mutex_lock(&ses->session_mutex);
		ses->dfs_root_ses = mnt_ctx->root_ses;
		mutex_unlock(&ses->session_mutex);
	}
	return rc;
}

static void set_root_ses(struct cifs_mount_ctx *mnt_ctx)
{
	if (mnt_ctx->ses) {
		spin_lock(&cifs_tcp_ses_lock);
		mnt_ctx->ses->ses_count++;
		spin_unlock(&cifs_tcp_ses_lock);
		dfs_cache_add_refsrv_session(&mnt_ctx->mount_id, mnt_ctx->ses);
	}
	mnt_ctx->root_ses = mnt_ctx->ses;
}

static int get_dfs_conn(struct cifs_mount_ctx *mnt_ctx, const char *ref_path, const char *full_path,
			const struct dfs_cache_tgt_iterator *tit)
{
	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
	struct dfs_info3_param ref = {};
	int rc;

	rc = dfs_cache_get_tgt_referral(ref_path + 1, tit, &ref);
	if (rc)
		return rc;

	rc = dfs_parse_target_referral(full_path + 1, &ref, ctx);
	if (rc)
		goto out;

	cifs_mount_put_conns(mnt_ctx);
	rc = get_session(mnt_ctx, ref_path);
	if (rc)
		goto out;

	if (ref.flags & DFSREF_REFERRAL_SERVER)
		set_root_ses(mnt_ctx);

	rc = -EREMOTE;
	if (ref.flags & DFSREF_STORAGE_SERVER) {
		rc = cifs_mount_get_tcon(mnt_ctx);
		if (rc)
			goto out;

		/* some servers may not advertise referral capability under ref.flags */
		if (!(ref.flags & DFSREF_REFERRAL_SERVER) &&
		    is_tcon_dfs(mnt_ctx->tcon))
			set_root_ses(mnt_ctx);

		rc = cifs_is_path_remote(mnt_ctx);
	}

out:
	free_dfs_info_param(&ref);
	return rc;
}

static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
{
	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
	char *ref_path = NULL, *full_path = NULL;
	struct dfs_cache_tgt_iterator *tit;
	struct TCP_Server_Info *server;
	char *origin_fullpath = NULL;
	int num_links = 0;
	int rc;

	ref_path = dfs_get_path(cifs_sb, ctx->UNC);
	if (IS_ERR(ref_path))
		return PTR_ERR(ref_path);

	full_path = build_unc_path_to_root(ctx, cifs_sb, true);
	if (IS_ERR(full_path)) {
		rc = PTR_ERR(full_path);
		full_path = NULL;
		goto out;
	}

	origin_fullpath = kstrdup(full_path, GFP_KERNEL);
	if (!origin_fullpath) {
		rc = -ENOMEM;
		goto out;
	}

	do {
		struct dfs_cache_tgt_list tl = DFS_CACHE_TGT_LIST_INIT(tl);

		rc = dfs_get_referral(mnt_ctx, ref_path + 1, NULL, &tl);
		if (rc)
			break;

		tit = dfs_cache_get_tgt_iterator(&tl);
		if (!tit) {
			cifs_dbg(VFS, "%s: dfs referral (%s) with no targets\n", __func__,
				 ref_path + 1);
			rc = -ENOENT;
			dfs_cache_free_tgts(&tl);
			break;
		}

		do {
			rc = get_dfs_conn(mnt_ctx, ref_path, full_path, tit);
			if (!rc)
				break;
			if (rc == -EREMOTE) {
				if (++num_links > MAX_NESTED_LINKS) {
					rc = -ELOOP;
					break;
				}
				kfree(ref_path);
				kfree(full_path);
				ref_path = full_path = NULL;

				full_path = build_unc_path_to_root(ctx, cifs_sb, true);
				if (IS_ERR(full_path)) {
					rc = PTR_ERR(full_path);
					full_path = NULL;
				} else {
					ref_path = dfs_get_path(cifs_sb, full_path);
					if (IS_ERR(ref_path)) {
						rc = PTR_ERR(ref_path);
						ref_path = NULL;
					}
				}
				break;
			}
		} while ((tit = dfs_cache_get_next_tgt(&tl, tit)));
		dfs_cache_free_tgts(&tl);
	} while (rc == -EREMOTE);

	if (!rc) {
		server = mnt_ctx->server;

		mutex_lock(&server->refpath_lock);
		server->origin_fullpath = origin_fullpath;
		server->current_fullpath = server->leaf_fullpath;
		mutex_unlock(&server->refpath_lock);
		origin_fullpath = NULL;
	}

out:
	kfree(origin_fullpath);
	kfree(ref_path);
	kfree(full_path);
	return rc;
}

int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
{
	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
	int rc;

	*isdfs = false;

	rc = get_session(mnt_ctx, NULL);
	if (rc)
		return rc;
	mnt_ctx->root_ses = mnt_ctx->ses;
	/*
	 * If called with 'nodfs' mount option, then skip DFS resolving.  Otherwise unconditionally
	 * try to get an DFS referral (even cached) to determine whether it is an DFS mount.
	 *
	 * Skip prefix path to provide support for DFS referrals from w2k8 servers which don't seem
	 * to respond with PATH_NOT_COVERED to requests that include the prefix.
	 */
	if ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) ||
	    dfs_get_referral(mnt_ctx, ctx->UNC + 1, NULL, NULL)) {
		rc = cifs_mount_get_tcon(mnt_ctx);
		if (rc)
			return rc;

		rc = cifs_is_path_remote(mnt_ctx);
		if (!rc || rc != -EREMOTE)
			return rc;
	}

	*isdfs = true;
	set_root_ses(mnt_ctx);

	return __dfs_mount_share(mnt_ctx);
}

/* Update dfs referral path of superblock */
static int update_server_fullpath(struct TCP_Server_Info *server, struct cifs_sb_info *cifs_sb,
				  const char *target)
{
	int rc = 0;
	size_t len = strlen(target);
	char *refpath, *npath;

	if (unlikely(len < 2 || *target != '\\'))
		return -EINVAL;

	if (target[1] == '\\') {
		len += 1;
		refpath = kmalloc(len, GFP_KERNEL);
		if (!refpath)
			return -ENOMEM;

		scnprintf(refpath, len, "%s", target);
	} else {
		len += sizeof("\\");
		refpath = kmalloc(len, GFP_KERNEL);
		if (!refpath)
			return -ENOMEM;

		scnprintf(refpath, len, "\\%s", target);
	}

	npath = dfs_cache_canonical_path(refpath, cifs_sb->local_nls, cifs_remap(cifs_sb));
	kfree(refpath);

	if (IS_ERR(npath)) {
		rc = PTR_ERR(npath);
	} else {
		mutex_lock(&server->refpath_lock);
		kfree(server->leaf_fullpath);
		server->leaf_fullpath = npath;
		mutex_unlock(&server->refpath_lock);
		server->current_fullpath = server->leaf_fullpath;
	}
	return rc;
}

static int target_share_matches_server(struct TCP_Server_Info *server, char *share,
				       bool *target_match)
{
	int rc = 0;
	const char *dfs_host;
	size_t dfs_host_len;

	*target_match = true;
	extract_unc_hostname(share, &dfs_host, &dfs_host_len);

	/* Check if hostnames or addresses match */
	cifs_server_lock(server);
	if (dfs_host_len != strlen(server->hostname) ||
	    strncasecmp(dfs_host, server->hostname, dfs_host_len)) {
		cifs_dbg(FYI, "%s: %.*s doesn't match %s\n", __func__,
			 (int)dfs_host_len, dfs_host, server->hostname);
		rc = match_target_ip(server, dfs_host, dfs_host_len, target_match);
		if (rc)
			cifs_dbg(VFS, "%s: failed to match target ip: %d\n", __func__, rc);
	}
	cifs_server_unlock(server);
	return rc;
}

static int __tree_connect_dfs_target(const unsigned int xid, struct cifs_tcon *tcon,
				     struct cifs_sb_info *cifs_sb, char *tree, bool islink,
				     struct dfs_cache_tgt_list *tl)
{
	int rc;
	struct TCP_Server_Info *server = tcon->ses->server;
	const struct smb_version_operations *ops = server->ops;
	struct cifs_ses *root_ses = CIFS_DFS_ROOT_SES(tcon->ses);
	struct cifs_tcon *ipc = root_ses->tcon_ipc;
	char *share = NULL, *prefix = NULL;
	struct dfs_cache_tgt_iterator *tit;
	bool target_match;

	tit = dfs_cache_get_tgt_iterator(tl);
	if (!tit) {
		rc = -ENOENT;
		goto out;
	}

	/* Try to tree connect to all dfs targets */
	for (; tit; tit = dfs_cache_get_next_tgt(tl, tit)) {
		const char *target = dfs_cache_get_tgt_name(tit);
		struct dfs_cache_tgt_list ntl = DFS_CACHE_TGT_LIST_INIT(ntl);

		kfree(share);
		kfree(prefix);
		share = prefix = NULL;

		/* Check if share matches with tcp ses */
		rc = dfs_cache_get_tgt_share(server->current_fullpath + 1, tit, &share, &prefix);
		if (rc) {
			cifs_dbg(VFS, "%s: failed to parse target share: %d\n", __func__, rc);
			break;
		}

		rc = target_share_matches_server(server, share, &target_match);
		if (rc)
			break;
		if (!target_match) {
			rc = -EHOSTUNREACH;
			continue;
		}

		dfs_cache_noreq_update_tgthint(server->current_fullpath + 1, tit);

		if (ipc->need_reconnect) {
			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", server->hostname);
			rc = ops->tree_connect(xid, ipc->ses, tree, ipc, cifs_sb->local_nls);
			cifs_dbg(FYI, "%s: reconnect ipc: %d\n", __func__, rc);
		}

		scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
		if (!islink) {
			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, cifs_sb->local_nls);
			break;
		}
		/*
		 * If no dfs referrals were returned from link target, then just do a TREE_CONNECT
		 * to it.  Otherwise, cache the dfs referral and then mark current tcp ses for
		 * reconnect so either the demultiplex thread or the echo worker will reconnect to
		 * newly resolved target.
		 */
		if (dfs_cache_find(xid, root_ses, cifs_sb->local_nls, cifs_remap(cifs_sb), target,
				   NULL, &ntl)) {
			rc = ops->tree_connect(xid, tcon->ses, tree, tcon, cifs_sb->local_nls);
			if (rc)
				continue;

			rc = cifs_update_super_prepath(cifs_sb, prefix);
		} else {
			/* Target is another dfs share */
			rc = update_server_fullpath(server, cifs_sb, target);
			dfs_cache_free_tgts(tl);

			if (!rc) {
				rc = -EREMOTE;
				list_replace_init(&ntl.tl_list, &tl->tl_list);
			} else
				dfs_cache_free_tgts(&ntl);
		}
		break;
	}

out:
	kfree(share);
	kfree(prefix);

	return rc;
}

static int tree_connect_dfs_target(const unsigned int xid, struct cifs_tcon *tcon,
				   struct cifs_sb_info *cifs_sb, char *tree, bool islink,
				   struct dfs_cache_tgt_list *tl)
{
	int rc;
	int num_links = 0;
	struct TCP_Server_Info *server = tcon->ses->server;
	char *old_fullpath = server->leaf_fullpath;

	do {
		rc = __tree_connect_dfs_target(xid, tcon, cifs_sb, tree, islink, tl);
		if (!rc || rc != -EREMOTE)
			break;
	} while (rc = -ELOOP, ++num_links < MAX_NESTED_LINKS);
	/*
	 * If we couldn't tree connect to any targets from last referral path, then
	 * retry it from newly resolved dfs referral.
	 */
	if (rc && server->leaf_fullpath != old_fullpath)
		cifs_signal_cifsd_for_reconnect(server, true);

	dfs_cache_free_tgts(tl);
	return rc;
}

int cifs_tree_connect(const unsigned int xid, struct cifs_tcon *tcon, const struct nls_table *nlsc)
{
	int rc;
	struct TCP_Server_Info *server = tcon->ses->server;
	const struct smb_version_operations *ops = server->ops;
	struct super_block *sb = NULL;
	struct cifs_sb_info *cifs_sb;
	struct dfs_cache_tgt_list tl = DFS_CACHE_TGT_LIST_INIT(tl);
	char *tree;
	struct dfs_info3_param ref = {0};

	/* only send once per connect */
	spin_lock(&tcon->tc_lock);
	if (tcon->ses->ses_status != SES_GOOD ||
	    (tcon->status != TID_NEW &&
	    tcon->status != TID_NEED_TCON)) {
		spin_unlock(&tcon->tc_lock);
		return 0;
	}
	tcon->status = TID_IN_TCON;
	spin_unlock(&tcon->tc_lock);

	tree = kzalloc(MAX_TREE_SIZE, GFP_KERNEL);
	if (!tree) {
		rc = -ENOMEM;
		goto out;
	}

	if (tcon->ipc) {
		cifs_server_lock(server);
		scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$", server->hostname);
		cifs_server_unlock(server);
		rc = ops->tree_connect(xid, tcon->ses, tree, tcon, nlsc);
		goto out;
	}

	sb = cifs_get_tcp_super(server);
	if (IS_ERR(sb)) {
		rc = PTR_ERR(sb);
		cifs_dbg(VFS, "%s: could not find superblock: %d\n", __func__, rc);
		goto out;
	}

	cifs_sb = CIFS_SB(sb);

	/* If it is not dfs or there was no cached dfs referral, then reconnect to same share */
	if (!server->current_fullpath ||
	    dfs_cache_noreq_find(server->current_fullpath + 1, &ref, &tl)) {
		rc = ops->tree_connect(xid, tcon->ses, tcon->tree_name, tcon, cifs_sb->local_nls);
		goto out;
	}

	rc = tree_connect_dfs_target(xid, tcon, cifs_sb, tree, ref.server_type == DFS_TYPE_LINK,
				     &tl);
	free_dfs_info_param(&ref);

out:
	kfree(tree);
	cifs_put_tcp_super(sb);

	if (rc) {
		spin_lock(&tcon->tc_lock);
		if (tcon->status == TID_IN_TCON)
			tcon->status = TID_NEED_TCON;
		spin_unlock(&tcon->tc_lock);
	} else {
		spin_lock(&tcon->tc_lock);
		if (tcon->status == TID_IN_TCON)
			tcon->status = TID_GOOD;
		spin_unlock(&tcon->tc_lock);
		tcon->need_reconnect = false;
	}

	return rc;
}