2.4.21-rc4 close race between sys_init_module and search_exception_table
PATCH 1/1 2.4.21-rc4 close race between sys_init_module and search_exception_table
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
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) renamed from 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) +17 -4
@@ -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: