ANDROID: overlayfs: inode_owner_or_capable called during execv

Using old_creds as an indication that we are not overriding the
credentials, bypass call to inode_owner_or_capable.  This solves
a problem with all execv calls being blocked when using the caller's
credentials.

Bug: 297913716
Link: https://lore.kernel.org/lkml/20201021151903.652827-5-salyzyn@android.com/
Change-Id: I1ae009a33a55da7404033e574c8873b079c795be
Signed-off-by: David Anderson <dvander@google.com>
Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Signed-off-by: Daniel Roseberg <drosen@google.com>
Test: adb-remount-test.sh

fs/overlayfs/file.c

@@ -60,7 +60,8 @@ static struct file *ovl_open_realfile(const struct file *file,
 	if (err) {
 		realfile = ERR_PTR(err);
 	} else {
-		if (!inode_owner_or_capable(real_idmap, realinode))
+		if (old_cred && !inode_owner_or_capable(real_idmap,
+							realinode))
 			flags &= ~O_NOATIME;
 
 		realfile = backing_file_open(&file->f_path, flags, realpath,