smb: client: fix regression with native SMB symlinks

Some users and customers reported that their backup/copy tools started
to fail when the directory being copied contained symlink targets that
the client couldn't parse - even when those symlinks weren't followed.

Fix this by allowing lstat(2) and readlink(2) to succeed even when the
client can't resolve the symlink target, restoring old behavior.

Cc: linux-cifs@vger.kernel.org
Cc: stable@vger.kernel.org
Reported-by: Remy Monsen <monsen@monsen.cc>
Closes: https://lore.kernel.org/r/CAN+tdP7y=jqw3pBndZAGjQv0ObFq8Q=+PUDHgB36HdEz9QA6FQ@mail.gmail.com
Reported-by: Pierguido Lambri <plambri@redhat.com>
Fixes: 12b466eb52 ("cifs: Fix creating and resolving absolute NT-style symlinks")
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/reparse.c

@@ -875,15 +875,8 @@ globalroot:
 			abs_path += sizeof("\\DosDevices\\")-1;
 		else if (strstarts(abs_path, "\\GLOBAL??\\"))
 			abs_path += sizeof("\\GLOBAL??\\")-1;
-		else {
-			/* Unhandled absolute symlink, points outside of DOS/Win32 */
-			cifs_dbg(VFS,
-				 "absolute symlink '%s' cannot be converted from NT format "
-				 "because points to unknown target\n",
-				 smb_target);
-			rc = -EIO;
-			goto out;
-		}
+		else
+			goto out_unhandled_target;
 
 		/* Sometimes path separator after \?? is double backslash */
 		if (abs_path[0] == '\\')
@@ -910,13 +903,7 @@ globalroot:
 			abs_path++;
 			abs_path[0] = drive_letter;
 		} else {
-			/* Unhandled absolute symlink. Report an error. */
-			cifs_dbg(VFS,
-				 "absolute symlink '%s' cannot be converted from NT format "
-				 "because points to unknown target\n",
-				 smb_target);
-			rc = -EIO;
-			goto out;
+			goto out_unhandled_target;
 		}
 
 		abs_path_len = strlen(abs_path)+1;
@@ -966,6 +953,7 @@ globalroot:
 		 * These paths have same format as Linux symlinks, so no
 		 * conversion is needed.
 		 */
+out_unhandled_target:
 		linux_target = smb_target;
 		smb_target = NULL;
 	}