cifs: introduce helper for finding referral server to improve DFS target resolution

Some servers seem to mistakenly report different values for
capabilities and share flags, so we can't always rely on those values
to decide whether the resolved target can handle any new DFS
referrals.

Add a new helper is_referral_server() to check if all resolved targets
can handle new DFS referrals by directly looking at the
GET_DFS_REFERRAL.ReferralHeaderFlags value as specified in MS-DFSC
2.2.4 RESP_GET_DFS_REFERRAL in addition to is_tcon_dfs().

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Cc: stable@vger.kernel.org # 5.11
Signed-off-by: Steve French <stfrench@microsoft.com>

2 files changed, 51 insertions, 17 deletions

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 1a6d6e1e2c71..b2447cea45ae 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3333,6 +3333,33 @@ out:
 	return rc;
 }
 
+/* Check if resolved targets can handle any DFS referrals */
+static int is_referral_server(const char *ref_path, struct cifs_tcon *tcon, bool *ref_server)
+{
+	int rc;
+	struct dfs_info3_param ref = {0};
+
+	if (is_tcon_dfs(tcon)) {
+		*ref_server = true;
+	} else {
+		cifs_dbg(FYI, "%s: ref_path=%s\n", __func__, ref_path);
+
+		rc = dfs_cache_noreq_find(ref_path, &ref, NULL);
+		if (rc) {
+			cifs_dbg(VFS, "%s: dfs_cache_noreq_find: failed (rc=%d)\n", __func__, rc);
+			return rc;
+		}
+		cifs_dbg(FYI, "%s: ref.flags=0x%x\n", __func__, ref.flags);
+		/*
+		 * Check if all targets are capable of handling DFS referrals as per
+		 * MS-DFSC 2.2.4 RESP_GET_DFS_REFERRAL.
+		 */
+		*ref_server = !!(ref.flags & DFSREF_REFERRAL_SERVER);
+		free_dfs_info_param(&ref);
+	}
+	return 0;
+}
+
 int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
 {
 	int rc = 0;
@@ -3344,6 +3371,7 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
 	char *ref_path = NULL, *full_path = NULL;
 	char *oldmnt = NULL;
 	char *mntdata = NULL;
+	bool ref_server = false;
 
 	rc = mount_get_conns(ctx, cifs_sb, &xid, &server, &ses, &tcon);
 	/*
@@ -3409,11 +3437,16 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
 			break;
 		if (!tcon)
 			continue;
+
 		/* Make sure that requests go through new root servers */
-		if (is_tcon_dfs(tcon)) {
+		rc = is_referral_server(ref_path + 1, tcon, &ref_server);
+		if (rc)
+			break;
+		if (ref_server) {
 			put_root_ses(root_ses);
 			set_root_ses(cifs_sb, ses, &root_ses);
 		}
+
 		/* Get next dfs path and then continue chasing them if -EREMOTE */
 		rc = next_dfs_prepath(cifs_sb, ctx, xid, server, tcon, &ref_path);
 		/* Prevent recursion on broken link referrals */
diff --git a/fs/cifs/dfs_cache.c b/fs/cifs/dfs_cache.c
index 4950ab0486ae..098b4bc8da59 100644
--- a/fs/cifs/dfs_cache.c
+++ b/fs/cifs/dfs_cache.c
@@ -37,11 +37,12 @@ struct cache_dfs_tgt {
 struct cache_entry {
 	struct hlist_node hlist;
 	const char *path;
-	int ttl;
-	int srvtype;
-	int flags;
+	int hdr_flags; /* RESP_GET_DFS_REFERRAL.ReferralHeaderFlags */
+	int ttl; /* DFS_REREFERRAL_V3.TimeToLive */
+	int srvtype; /* DFS_REREFERRAL_V3.ServerType */
+	int ref_flags; /* DFS_REREFERRAL_V3.ReferralEntryFlags */
 	struct timespec64 etime;
-	int path_consumed;
+	int path_consumed; /* RESP_GET_DFS_REFERRAL.PathConsumed */
 	int numtgts;
 	struct list_head tlist;
 	struct cache_dfs_tgt *tgthint;
@@ -166,14 +167,11 @@ static int dfscache_proc_show(struct seq_file *m, void *v)
 				continue;
 
 			seq_printf(m,
-				   "cache entry: path=%s,type=%s,ttl=%d,etime=%ld,"
-				   "interlink=%s,path_consumed=%d,expired=%s\n",
-				   ce->path,
-				   ce->srvtype == DFS_TYPE_ROOT ? "root" : "link",
-				   ce->ttl, ce->etime.tv_nsec,
-				   IS_INTERLINK_SET(ce->flags) ? "yes" : "no",
-				   ce->path_consumed,
-				   cache_entry_expired(ce) ? "yes" : "no");
+				   "cache entry: path=%s,type=%s,ttl=%d,etime=%ld,hdr_flags=0x%x,ref_flags=0x%x,interlink=%s,path_consumed=%d,expired=%s\n",
+				   ce->path, ce->srvtype == DFS_TYPE_ROOT ? "root" : "link",
+				   ce->ttl, ce->etime.tv_nsec, ce->ref_flags, ce->hdr_flags,
+				   IS_INTERLINK_SET(ce->hdr_flags) ? "yes" : "no",
+				   ce->path_consumed, cache_entry_expired(ce) ? "yes" : "no");
 
 			list_for_each_entry(t, &ce->tlist, list) {
 				seq_printf(m, "  %s%s\n",
@@ -236,11 +234,12 @@ static inline void dump_tgts(const struct cache_entry *ce)
 
 static inline void dump_ce(const struct cache_entry *ce)
 {
-	cifs_dbg(FYI, "cache entry: path=%s,type=%s,ttl=%d,etime=%ld,interlink=%s,path_consumed=%d,expired=%s\n",
+	cifs_dbg(FYI, "cache entry: path=%s,type=%s,ttl=%d,etime=%ld,hdr_flags=0x%x,ref_flags=0x%x,interlink=%s,path_consumed=%d,expired=%s\n",
 		 ce->path,
 		 ce->srvtype == DFS_TYPE_ROOT ? "root" : "link", ce->ttl,
 		 ce->etime.tv_nsec,
-		 IS_INTERLINK_SET(ce->flags) ? "yes" : "no",
+		 ce->hdr_flags, ce->ref_flags,
+		 IS_INTERLINK_SET(ce->hdr_flags) ? "yes" : "no",
 		 ce->path_consumed,
 		 cache_entry_expired(ce) ? "yes" : "no");
 	dump_tgts(ce);
@@ -381,7 +380,8 @@ static int copy_ref_data(const struct dfs_info3_param *refs, int numrefs,
 	ce->ttl = refs[0].ttl;
 	ce->etime = get_expire_time(ce->ttl);
 	ce->srvtype = refs[0].server_type;
-	ce->flags = refs[0].ref_flag;
+	ce->hdr_flags = refs[0].flags;
+	ce->ref_flags = refs[0].ref_flag;
 	ce->path_consumed = refs[0].path_consumed;
 
 	for (i = 0; i < numrefs; i++) {
@@ -799,7 +799,8 @@ static int setup_referral(const char *path, struct cache_entry *ce,
 	ref->path_consumed = ce->path_consumed;
 	ref->ttl = ce->ttl;
 	ref->server_type = ce->srvtype;
-	ref->ref_flag = ce->flags;
+	ref->ref_flag = ce->ref_flags;
+	ref->flags = ce->hdr_flags;
 
 	return 0;