interfaces: improve the error message when functionfs is usedallow-diagsfs

2 files changed, 5 insertions, 2 deletions

diff --git a/interfaces/builtin/mount_control.go b/interfaces/builtin/mount_control.go
index bfef9363ab..43c8d247a3 100644
--- a/interfaces/builtin/mount_control.go
+++ b/interfaces/builtin/mount_control.go
@@ -278,7 +278,10 @@ func validateWhatAttr(mountInfo *MountInfo) error {
	// with "functionfs" the "what" can essentially be anything, see
	// https://www.kernel.org/doc/html/latest/usb/functionfs.html
	if len(mountInfo.types) == 1 && mountInfo.types[0] == "functionfs" {
-	return apparmor_sandbox.ValidateNoAppArmorRegexp(what)
+	if err := apparmor_sandbox.ValidateNoAppArmorRegexp(what); err != nil {
+	return fmt.Errorf(`cannot use mount-control "what" attribute: %w`, err)
+	}
+	return nil
	}
 
	if !whatRegexp.MatchString(what) {
diff --git a/interfaces/builtin/mount_control_test.go b/interfaces/builtin/mount_control_test.go
index 447711c71e..42312ecc1f 100644
--- a/interfaces/builtin/mount_control_test.go
+++ b/interfaces/builtin/mount_control_test.go
@@ -262,7 +262,7 @@ func (s *MountControlInterfaceSuite) TestSanitizePlugUnhappy(c *C) {
	},
	{
	"mount:\n - what: a?\n where: /dev/ffs-diag\n type: [functionfs]\n options: [rw]",
-	`"a\?" contains a reserved apparmor char from.*`,
+	`cannot use mount-control "what" attribute: "a\?" contains a reserved apparmor char from.*`,
	},
	}