smb: client: ensure to try all targets when finding nested links

With current implementation, when a nested DFS link is found during
mount(2), the client follows the referral and then try to connect to
all of its targets.  If all targets failed, the client bails out
rather than retrying remaining targets from previous referral.

Fix this by stacking all referrals and targets so the client can retry
remaining targets from previous referrals in case all targets of
current referral have failed.

Thanks to samba, this can be easily tested like below

* Run the following under dfs folder in samba server

  $ ln -s "msdfs:srv\\bad-share" link1
  $ ln -s "msdfs:srv\\dfs\\link1,srv\\good-share" link0

* Before patch

  $ mount.cifs //srv/dfs/link0 /mnt -o ...
  mount error(2): No such file or directory
  Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)...

* After patch

  $ mount.cifs //srv/dfs/link0 /mnt -o ...
  # ls /mnt
  bar  fileshare1  sub

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 132 insertions, 119 deletions

diff --git a/fs/smb/client/dfs.c b/fs/smb/client/dfs.c
index c837800c49d4..71ee74041884 100644
--- a/fs/smb/client/dfs.c
+++ b/fs/smb/client/dfs.c
@@ -3,7 +3,6 @@
  * Copyright (c) 2022 Paulo Alcantara <palcantara@suse.de>
  */
 
-#include <linux/namei.h>
 #include "cifsproto.h"
 #include "cifs_debug.h"
 #include "dns_resolve.h"
@@ -96,51 +95,134 @@ static int add_root_smb_session(struct cifs_mount_ctx *mnt_ctx)
 	return 0;
 }
 
-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)
+static inline int parse_dfs_target(struct smb3_fs_context *ctx,
+				   struct dfs_ref_walk *rw,
+				   struct dfs_info3_param *tgt)
+{
+	int rc;
+	const char *fpath = ref_walk_fpath(rw) + 1;
+
+	rc = ref_walk_get_tgt(rw, tgt);
+	if (!rc)
+		rc = dfs_parse_target_referral(fpath, tgt, ctx);
+	return rc;
+}
+
+static int set_ref_paths(struct cifs_mount_ctx *mnt_ctx,
+			 struct dfs_info3_param *tgt,
+			 struct dfs_ref_walk *rw)
 {
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
-	struct dfs_info3_param ref = {};
-	bool is_refsrv;
-	int rc, rc2;
+	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
+	char *ref_path, *full_path;
+	int rc;
 
-	rc = dfs_cache_get_tgt_referral(ref_path + 1, tit, &ref);
-	if (rc)
+	full_path = smb3_fs_context_fullpath(ctx, CIFS_DIR_SEP(cifs_sb));
+	if (IS_ERR(full_path))
+		return PTR_ERR(full_path);
+
+	if (!tgt || (tgt->server_type == DFS_TYPE_LINK &&
+		     DFS_INTERLINK(tgt->flags)))
+		ref_path = dfs_get_path(cifs_sb, ctx->UNC);
+	else
+		ref_path = dfs_get_path(cifs_sb, full_path);
+	if (IS_ERR(ref_path)) {
+		rc = PTR_ERR(ref_path);
+		kfree(full_path);
 		return rc;
+	}
+	ref_walk_path(rw) = ref_path;
+	ref_walk_fpath(rw) = full_path;
+	return 0;
+}
 
-	rc = dfs_parse_target_referral(full_path + 1, &ref, ctx);
-	if (rc)
-		goto out;
+static int __dfs_referral_walk(struct cifs_mount_ctx *mnt_ctx,
+			       struct dfs_ref_walk *rw)
+{
+	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
+	struct dfs_info3_param tgt = {};
+	bool is_refsrv;
+	int rc = -ENOENT;
 
-	cifs_mount_put_conns(mnt_ctx);
-	rc = get_session(mnt_ctx, ref_path);
-	if (rc)
-		goto out;
+again:
+	do {
+		if (ref_walk_empty(rw)) {
+			rc = dfs_get_referral(mnt_ctx, ref_walk_path(rw) + 1,
+					      NULL, ref_walk_tl(rw));
+			if (rc) {
+				rc = cifs_mount_get_tcon(mnt_ctx);
+				if (!rc)
+					rc = cifs_is_path_remote(mnt_ctx);
+				continue;
+			}
+			if (!ref_walk_num_tgts(rw)) {
+				rc = -ENOENT;
+				continue;
+			}
+		}
 
-	is_refsrv = !!(ref.flags & DFSREF_REFERRAL_SERVER);
+		while (ref_walk_next_tgt(rw)) {
+			rc = parse_dfs_target(ctx, rw, &tgt);
+			if (rc)
+				continue;
 
-	rc = -EREMOTE;
-	if (ref.flags & DFSREF_STORAGE_SERVER) {
-		rc = cifs_mount_get_tcon(mnt_ctx);
-		if (rc)
-			goto out;
+			cifs_mount_put_conns(mnt_ctx);
+			rc = get_session(mnt_ctx, ref_walk_path(rw));
+			if (rc)
+				continue;
 
-		/* some servers may not advertise referral capability under ref.flags */
-		is_refsrv |= is_tcon_dfs(mnt_ctx->tcon);
+			is_refsrv = tgt.server_type == DFS_TYPE_ROOT ||
+				DFS_INTERLINK(tgt.flags);
+			ref_walk_set_tgt_hint(rw);
 
-		rc = cifs_is_path_remote(mnt_ctx);
-	}
+			if (tgt.flags & DFSREF_STORAGE_SERVER) {
+				rc = cifs_mount_get_tcon(mnt_ctx);
+				if (!rc)
+					rc = cifs_is_path_remote(mnt_ctx);
+				if (!rc)
+					break;
+				if (rc != -EREMOTE)
+					continue;
+			}
 
-	dfs_cache_noreq_update_tgthint(ref_path + 1, tit);
+			if (is_refsrv) {
+				rc = add_root_smb_session(mnt_ctx);
+				if (rc)
+					goto out;
+			}
 
-	if (rc == -EREMOTE && is_refsrv) {
-		rc2 = add_root_smb_session(mnt_ctx);
-		if (rc2)
-			rc = rc2;
-	}
+			rc = ref_walk_advance(rw);
+			if (!rc) {
+				rc = set_ref_paths(mnt_ctx, &tgt, rw);
+				if (!rc) {
+					rc = -EREMOTE;
+					goto again;
+				}
+			}
+			if (rc != -ELOOP)
+				goto out;
+		}
+	} while (rc && ref_walk_descend(rw));
 
 out:
-	free_dfs_info_param(&ref);
+	free_dfs_info_param(&tgt);
+	return rc;
+}
+
+static int dfs_referral_walk(struct cifs_mount_ctx *mnt_ctx)
+{
+	struct dfs_ref_walk *rw;
+	int rc;
+
+	rw = ref_walk_alloc();
+	if (IS_ERR(rw))
+		return PTR_ERR(rw);
+
+	ref_walk_init(rw);
+	rc = set_ref_paths(mnt_ctx, NULL, rw);
+	if (!rc)
+		rc = __dfs_referral_walk(mnt_ctx, rw);
+	ref_walk_free(rw);
 	return rc;
 }
 
@@ -148,105 +230,36 @@ 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 cifs_tcon *tcon;
-	char *origin_fullpath = NULL;
-	char sep = CIFS_DIR_SEP(cifs_sb);
-	int num_links = 0;
+	char *origin_fullpath;
 	int rc;
 
-	ref_path = dfs_get_path(cifs_sb, ctx->UNC);
-	if (IS_ERR(ref_path))
-		return PTR_ERR(ref_path);
+	origin_fullpath = dfs_get_path(cifs_sb, ctx->source);
+	if (IS_ERR(origin_fullpath))
+		return PTR_ERR(origin_fullpath);
 
-	full_path = smb3_fs_context_fullpath(ctx, sep);
-	if (IS_ERR(full_path)) {
-		rc = PTR_ERR(full_path);
-		full_path = NULL;
+	rc = dfs_referral_walk(mnt_ctx);
+	if (rc)
 		goto out;
-	}
 
-	origin_fullpath = kstrdup(full_path, GFP_KERNEL);
-	if (!origin_fullpath) {
-		rc = -ENOMEM;
-		goto out;
+	tcon = mnt_ctx->tcon;
+	spin_lock(&tcon->tc_lock);
+	if (!tcon->origin_fullpath) {
+		tcon->origin_fullpath = origin_fullpath;
+		origin_fullpath = NULL;
 	}
+	spin_unlock(&tcon->tc_lock);
 
-	do {
-		DFS_CACHE_TGT_LIST(tl);
-
-		rc = dfs_get_referral(mnt_ctx, ref_path + 1, NULL, &tl);
-		if (rc) {
-			rc = cifs_mount_get_tcon(mnt_ctx);
-			if (!rc)
-				rc = cifs_is_path_remote(mnt_ctx);
-			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 = smb3_fs_context_fullpath(ctx, sep);
-				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) {
-		tcon = mnt_ctx->tcon;
-
-		spin_lock(&tcon->tc_lock);
-		if (!tcon->origin_fullpath) {
-			tcon->origin_fullpath = origin_fullpath;
-			origin_fullpath = NULL;
-		}
-		spin_unlock(&tcon->tc_lock);
-
-		if (list_empty(&tcon->dfs_ses_list)) {
-			list_replace_init(&mnt_ctx->dfs_ses_list,
-					  &tcon->dfs_ses_list);
-			queue_delayed_work(dfscache_wq, &tcon->dfs_cache_work,
-					   dfs_cache_get_ttl() * HZ);
-		} else {
-			dfs_put_root_smb_sessions(&mnt_ctx->dfs_ses_list);
-		}
+	if (list_empty(&tcon->dfs_ses_list)) {
+		list_replace_init(&mnt_ctx->dfs_ses_list, &tcon->dfs_ses_list);
+		queue_delayed_work(dfscache_wq, &tcon->dfs_cache_work,
+				   dfs_cache_get_ttl() * HZ);
+	} else {
+		dfs_put_root_smb_sessions(&mnt_ctx->dfs_ses_list);
 	}
 
 out:
 	kfree(origin_fullpath);
-	kfree(ref_path);
-	kfree(full_path);
 	return rc;
 }