module: Prevent silent truncation of module name in delete_module(2)

Passing a module name longer than MODULE_NAME_LEN to the delete_module
syscall results in its silent truncation. This really isn't much of
a problem in practice, but it could theoretically lead to the removal of an
incorrect module. It is more sensible to return ENAMETOOLONG or ENOENT in
such a case.

Update the syscall to return ENOENT, as documented in the delete_module(2)
man page to mean "No module by that name exists." This is appropriate
because a module with a name longer than MODULE_NAME_LEN cannot be loaded
in the first place.

Signed-off-by: Petr Pavlu <[email protected]>
Reviewed-by: Daniel Gomez <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Daniel Gomez <[email protected]>

Author: petrpavlu

kernel/module/main.c

@@ -779,14 +779,16 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
 	struct module *mod;
 	char name[MODULE_NAME_LEN];
 	char buf[MODULE_FLAGS_BUF_SIZE];
-	int ret, forced = 0;
+	int ret, len, forced = 0;
 
 	if (!capable(CAP_SYS_MODULE) || modules_disabled)
 		return -EPERM;
 
-	if (strncpy_from_user(name, name_user, MODULE_NAME_LEN-1) < 0)
-		return -EFAULT;
-	name[MODULE_NAME_LEN-1] = '\0';
+	len = strncpy_from_user(name, name_user, MODULE_NAME_LEN);
+	if (len == 0 || len == MODULE_NAME_LEN)
+		return -ENOENT;
+	if (len < 0)
+		return len;
 
 	audit_log_kern_module(name);