[RFC PATCH v2 8/9] ksmbd: support trusted EAs

generic/093 uses "setfattr -n trusted.name" and getfattr to check that a
write does not clear the trusted xattr. ksmbd stores the attribute as
user.trusted.name on the backing filesystem.

Map trusted names to the trusted xattr namespace for set, get, and list
operations. Filter the internal POSIX ACL xattrs.

Signed-off-by: Ze Tan <[email protected]>
---
 fs/smb/server/smb2pdu.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index da3d5c217577..7b2baa317888 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -2643,6 +2643,19 @@ static noinline int create_smb2_pipe(struct ksmbd_work *work)
 	return err;
 }
 
+static bool ksmbd_is_internal_acl_ea_name(const char *name, size_t name_len)
+{
+	return (name_len == sizeof(XATTR_NAME_POSIX_ACL_ACCESS) - 1 &&
+		!strncmp(name, XATTR_NAME_POSIX_ACL_ACCESS, name_len)) ||
+	       (name_len == sizeof(XATTR_NAME_POSIX_ACL_DEFAULT) - 1 &&
+		!strncmp(name, XATTR_NAME_POSIX_ACL_DEFAULT, name_len)) ||
+	       (name_len == sizeof(XATTR_TRUSTED_PREFIX "SGI_ACL_FILE") - 1 &&
+		!strncmp(name, XATTR_TRUSTED_PREFIX "SGI_ACL_FILE", name_len)) ||
+	       (name_len == sizeof(XATTR_TRUSTED_PREFIX "SGI_ACL_DEFAULT") - 1 &&
+		!strncmp(name, XATTR_TRUSTED_PREFIX "SGI_ACL_DEFAULT",
+			 name_len));
+}
+
 static bool ksmbd_is_security_capability_ea_name(const char *name,
 						 size_t name_len)
 {
@@ -2665,6 +2678,18 @@ static bool ksmbd_is_posix_ea_name(const char *name, size_t name_len)
 	if (ksmbd_is_security_xfstests_ea_name(name, name_len))
 		return true;
 
+	/*
+	 * POSIX ACL xattrs are filesystem-internal ACL records, not
+	 * user-visible EAs.  XFS may also expose trusted.SGI_ACL_* aliases
+	 * through listxattr(), so filter those as well.
+	 */
+	if (ksmbd_is_internal_acl_ea_name(name, name_len))
+		return false;
+
+	if (name_len > XATTR_TRUSTED_PREFIX_LEN &&
+	    !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN))
+		return true;
+
 	return false;
 }
 
@@ -2672,6 +2697,9 @@ static int ksmbd_map_ea_name_to_xattr(bool posix_extensions,
 				      const char *ea_name, size_t ea_name_len,
 				      char *attr_name)
 {
+	if (ksmbd_is_internal_acl_ea_name(ea_name, ea_name_len))
+		return -EINVAL;
+
 	if (posix_extensions &&
 	    ksmbd_is_posix_ea_name(ea_name, ea_name_len)) {
 		if (ea_name_len > XATTR_NAME_MAX)
-- 
2.43.0