module: fix refptr allocation and release order

Impact: fix ref-after-free crash on failed module load

Fix refptr bug: Change refptr allocation and release order not to access a module
data structure pointed by 'mod' after freeing mod->module_core.
This bug will cause kernel panic(e.g. failed to find undefined symbols).

This bug was reported on systemtap bugzilla.
http://sources.redhat.com/bugzilla/show_bug.cgi?id=9927

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/kernel/module.c b/kernel/module.c
index ba22484..1196f5d 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2015,14 +2015,6 @@ static noinline struct module *load_module(void __user *umod,
        if (err < 0)
                goto free_mod;
 
-#if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
-       mod->refptr = percpu_modalloc(sizeof(local_t), __alignof__(local_t),
-                                     mod->name);
-       if (!mod->refptr) {
-               err = -ENOMEM;
-               goto free_mod;
-       }
-#endif
        if (pcpuindex) {
                /* We have a special allocation for this section. */
                percpu = percpu_modalloc(sechdrs[pcpuindex].sh_size,
@@ -2030,7 +2022,7 @@ static noinline struct module *load_module(void __user *umod,
                                         mod->name);
                if (!percpu) {
                        err = -ENOMEM;
-                       goto free_percpu;
+                       goto free_mod;
                }
                sechdrs[pcpuindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
                mod->percpu = percpu;
@@ -2082,6 +2074,14 @@ static noinline struct module *load_module(void __user *umod,
        /* Module has been moved. */
        mod = (void *)sechdrs[modindex].sh_addr;
 
+#if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
+       mod->refptr = percpu_modalloc(sizeof(local_t), __alignof__(local_t),
+                                     mod->name);
+       if (!mod->refptr) {
+               err = -ENOMEM;
+               goto free_init;
+       }
+#endif
        /* Now we've moved module, initialize linked lists, etc. */
        module_unload_init(mod);
 
@@ -2288,15 +2288,17 @@ static noinline struct module *load_module(void __user *umod,
        ftrace_release(mod->module_core, mod->core_size);
  free_unload:
        module_unload_free(mod);
+ free_init:
+#if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
+       percpu_modfree(mod->refptr);
+#endif
        module_free(mod, mod->module_init);
  free_core:
        module_free(mod, mod->module_core);
+       /* mod will be freed with core. Don't access it beyond this line! */
  free_percpu:
        if (percpu)
                percpu_modfree(percpu);
-#if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
-       percpu_modfree(mod->refptr);
-#endif
  free_mod:
        kfree(args);
  free_hdr: