cifs: share dfs connections and supers

When matching DFS superblocks we can't rely on either the server's
address or tcon's UNC name from mount(2) as the existing servers and
tcons might be connected to somewhere else.  Instead, check if
superblock is dfs, and if so, match its original source pathname with
the new mount's source pathname.

For DFS connections, instead of checking server's address, match its
referral path as it could be connected to different targets.

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

1 files changed, 226 insertions, 0 deletions

diff --git a/fs/cifs/dfs.c b/fs/cifs/dfs.c
index ce21438cadec..88a0cab335b4 100644
--- a/fs/cifs/dfs.c
+++ b/fs/cifs/dfs.c
@@ -3,6 +3,7 @@
  * Copyright (c) 2022 Paulo Alcantara <palcantara@suse.de>
  */
 
+#include <linux/namei.h>
 #include "cifsproto.h"
 #include "cifs_debug.h"
 #include "dns_resolve.h"
@@ -52,3 +53,228 @@ 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;
+
+	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);
+}