cifs: sanitize paths in cifs_update_super_prepath.

After a server reboot, clients are failing to move files with ENOENT.
This is caused by DFS referrals containing multiple separators, which
the server move call doesn't recognize.

v1: Initial patch.
v2: Move prototype to header.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2182472
Fixes: a310808 ("cifs: sanitize multiple delimiters in prepath")
Actually-Fixes: 24e0a1e ("cifs: switch to new mount api")
Reviewed-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Thiago Rafael Becker <tbecker@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/fs_context.c

@@ -441,13 +441,14 @@ int smb3_parse_opt(const char *options, const char *key, char **val)
  * but there are some bugs that prevent rename from working if there are
  * multiple delimiters.
  *
- * Returns a sanitized duplicate of @path. The caller is responsible for
- * cleaning up the original.
+ * Returns a sanitized duplicate of @path. @gfp indicates the GFP_* flags
+ * for kstrdup.
+ * The caller is responsible for freeing the original.
  */
 #define IS_DELIM(c) ((c) == '/' || (c) == '\\')
-static char *sanitize_path(char *path)
+char *cifs_sanitize_prepath(char *prepath, gfp_t gfp)
 {
-	char *cursor1 = path, *cursor2 = path;
+	char *cursor1 = prepath, *cursor2 = prepath;
 
 	/* skip all prepended delimiters */
 	while (IS_DELIM(*cursor1))
@@ -469,7 +470,7 @@ static char *sanitize_path(char *path)
 		cursor2--;
 
 	*(cursor2) = '\0';
-	return kstrdup(path, GFP_KERNEL);
+	return kstrdup(prepath, gfp);
 }
 
 /*
@@ -531,7 +532,7 @@ smb3_parse_devname(const char *devname, struct smb3_fs_context *ctx)
 	if (!*pos)
 		return 0;
 
-	ctx->prepath = sanitize_path(pos);
+	ctx->prepath = cifs_sanitize_prepath(pos, GFP_KERNEL);
 	if (!ctx->prepath)
 		return -ENOMEM;
 

fs/cifs/fs_context.h

@@ -287,4 +287,7 @@ extern void smb3_update_mnt_flags(struct cifs_sb_info *cifs_sb);
  */
 #define SMB3_MAX_DCLOSETIMEO (1 << 30)
 #define SMB3_DEF_DCLOSETIMEO (1 * HZ) /* even 1 sec enough to help eg open/write/close/open/read */
+
+extern char *cifs_sanitize_prepath(char *prepath, gfp_t gfp);
+
 #endif

fs/cifs/misc.c

@@ -1195,7 +1195,7 @@ int cifs_update_super_prepath(struct cifs_sb_info *cifs_sb, char *prefix)
 	kfree(cifs_sb->prepath);
 
 	if (prefix && *prefix) {
-		cifs_sb->prepath = kstrdup(prefix, GFP_ATOMIC);
+		cifs_sb->prepath = cifs_sanitize_prepath(prefix, GFP_ATOMIC);
 		if (!cifs_sb->prepath)
 			return -ENOMEM;