Copying a module from user space directly into the kernel breaks the
module_list chain for several hundred cycles. Another cpu can call
search_exception_table() and get an oops because the chain of exception
entries is broken, we do not even find the kernel exception tables!
This race has been there for a _long_ time, since at least 2.2.0. It
was found by SGI QE stress tests, doing repeated module load and unload.
Patch is against 2.4.21-rc4, it fits 2.4.20 with offsets.
Index: 21-rc4.1/kernel/module.c
--- 21-rc4.1/kernel/module.c Wed, 11 Dec 2002 11:38:55 +1100 kaos (linux-2.4/j/45_module.c 1.1.2.1.3.1.3.1.1.1.2.2 644)
+++ 21-rc4.1(w)/kernel/module.c Tue, 27 May 2003 16:54:55 +1000 kaos (linux-2.4/j/45_module.c 1.1.2.1.3.1.3.1.1.1.2.2 644)
@@ -345,10 +345,10 @@ err0:
asmlinkage long
sys_init_module(const char *name_user, struct module *mod_user)
{
- struct module mod_tmp, *mod;
+ struct module mod_tmp, *mod, *mod2 = NULL;
char *name, *n_name, *name_tmp = NULL;
long namelen, n_namelen, i, error;
- unsigned long mod_user_size;
+ unsigned long mod_user_size, flags;
struct module_ref *dep;
if (!capable(CAP_SYS_MODULE))
@@ -387,11 +387,23 @@ sys_init_module(const char *name_user, s
}
strcpy(name_tmp, mod->name);
- error = copy_from_user(mod, mod_user, mod_user_size);
+ /* Copying mod_user directly over mod breaks the module_list chain and
+ * races against search_exception_table. copy_from_user may sleep so it
+ * cannot be under modlist_lock, do the copy in two stages.
+ */
+ if (!(mod2 = vmalloc(mod_user_size))) {
+ error = -ENOMEM;
+ goto err2;
+ }
+ error = copy_from_user(mod2, mod_user, mod_user_size);
if (error) {
error = -EFAULT;
goto err2;
}
+ spin_lock_irqsave(&modlist_lock, flags);
+ memcpy(mod, mod2, mod_user_size);
+ mod->next = mod_tmp.next;
+ spin_unlock_irqrestore(&modlist_lock, flags);
/* Sanity check the size of the module. */
error = -EINVAL;
@@ -505,7 +517,6 @@ sys_init_module(const char *name_user, s
to make the I and D caches consistent. */
flush_icache_range((unsigned long)mod, (unsigned long)mod + mod->size);
- mod->next = mod_tmp.next;
mod->refs = NULL;
/* Sanity check the module's dependents */
@@ -566,6 +577,8 @@ sys_init_module(const char *name_user, s
err3:
put_mod_name(n_name);
err2:
+ if (mod2)
+ vfree(mod2);
*mod = mod_tmp;
strcpy((char *)mod->name, name_tmp); /* We know there is room for this */
err1: