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>

1 files changed, 14 insertions, 12 deletions

diff --git a/kernel/module.c b/kernel/module.c
index ba22484a987e..1196f5d11700 100644
--- 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: