[PATCH] ovl: fix trusted xattr escape prefix matching

[Yichong Chen <chenyichong@uniontech.com>]

In the trusted.* xattr namespace, ovl_is_escaped_xattr() compares
one byte less than the escaped overlay xattr prefix length. This makes
it match "trusted.overlay.overlay" without requiring the trailing dot.

As a result, an xattr such as "trusted.overlay.overlayfoo" is
incorrectly treated as an escaped overlay xattr. This can be reproduced
by setting "trusted.overlay.overlayfoo" on a lower file and listing xattrs
through an overlay mount. listxattr() then exposes it as
"trusted.overlay.oo", and a following getxattr() on that listed name fails
with ENODATA.

Compare the full escaped prefix, including the trailing dot, so
similarly-prefixed private xattrs are not misclassified.

Fixes: dad02fad84cbc ("ovl: Support escaped overlay.* xattrs")
Signed-off-by: Yichong Chen <chenyichong@uniontech.com>
---
 fs/overlayfs/xattrs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/xattrs.c b/fs/overlayfs/xattrs.c
index aa95855c7023..859e80ae6f40 100644
--- a/fs/overlayfs/xattrs.c
+++ b/fs/overlayfs/xattrs.c
@@ -13,7 +13,7 @@ static bool ovl_is_escaped_xattr(struct super_block *sb, const char *name)
 			       OVL_XATTR_ESCAPE_USER_PREFIX_LEN) == 0;
 	else
 		return strncmp(name, OVL_XATTR_ESCAPE_TRUSTED_PREFIX,
-			       OVL_XATTR_ESCAPE_TRUSTED_PREFIX_LEN - 1) == 0;
+			       OVL_XATTR_ESCAPE_TRUSTED_PREFIX_LEN) == 0;
 }
 
 static bool ovl_is_own_xattr(struct super_block *sb, const char *name)
-- 
2.51.0