[patch] 2.4.18/2.5.24 kernel/module.c - minor bugs

[Peter Oberparleiter]

Hi,

this patch fixes two minor bugs in kernel/module.c in current linux
kernel versions (2.4.18/2.5.24) which could cause problems in some
rare situations:

1. A size-check in sys_create_module is off by one. The check reads

        if (size < sizeof(struct module)+namelen) {
                error = -EINVAL;
                goto err1;
        }

while a subsequent write to a "size"-long buffer expects one more
byte ("mod" being the buffer pointer of type struct module*):

        memcpy((char*)(mod+1), name, namelen+1);

2. In case "struct module" used by insmod is larger than the one used
by the kernel (e.g. newer version), module loading will fail.

This is because sys_create_module initializes the module buffer with 

                      0:  struct module
  sizeof(struct module):  char[] module_name

while sys_init_module copies the insmod-provided "struct module" data into
this buffer, overwriting the adjacent module name with the extra "struct
module" fields. As a result, the following sanity check will fail

        if (namelen != n_namelen || strcmp(n_name, mod_tmp.name) != 0) {
                printk(KERN_ERR "init_module: changed module name to "
                                "%s' from %s'\n",
                       n_name, mod_tmp.name);
                goto err3;
        }

because mod_tmp.name points to the overwritten module name.

This can be easily fixed using the already existing copy of the module name
in "name_tmp".

Following is the patch implementing these two fixes (diff against 2.4.17,
works for 2.4.18, 2.5.24):

========================================
--- linux-2.4.17/kernel/module.c	Sun Nov 11 20:23:14 2001
+++ linux-2.4.17-modfix/kernel/module.c	Mon Jul  8 09:50:57 2002
@@ -303,7 +303,7 @@
 		error = namelen;
 		goto err0;
 	}
-	if (size < sizeof(struct module)+namelen) {
+	if (size < sizeof(struct module)+namelen+1) {
 		error = -EINVAL;
 		goto err1;
 	}
@@ -482,10 +482,10 @@
 		error = n_namelen;
 		goto err2;
 	}
-	if (namelen != n_namelen || strcmp(n_name, mod_tmp.name) != 0) {
+	if (namelen != n_namelen || strcmp(n_name, name_tmp) != 0) {
 		printk(KERN_ERR "init_module: changed module name to "
 				"`%s' from `%s'\n",
-		       n_name, mod_tmp.name);
+		       n_name, name_tmp);
 		goto err3;
 	}
 
========================================

Regards,
  Peter Oberparleiter