[PATCH] module: fix refptr allocation and release order

[PATCH] module: fix refptr allocation and release order

[Rusty Russell]

From: Masami Hiramatsu <mhiramat@redhat.com>

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
--- 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:

Re: [PATCH] module: fix refptr allocation and release order

[Eric Dumazet]

Rusty Russell a écrit :
> From: Masami Hiramatsu <mhiramat@redhat.com>
> 
> 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>


My original patch did not have this problem, because I used a local variable
to hold refptr.

http://www.archivum.info/linux-kernel@vger.kernel.org/2008-05/msg07400.html

A simpler patch could just use a local variable again, since we are very
late in rc phase ?


From: Masami Hiramatsu <mhiramat@redhat.com>

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

Fix refptr bug: Change refptr release 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>
Signed-off-by: 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..4dd1228 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1874,6 +1874,9 @@ static noinline struct module *load_module(void __user *umod,
 	struct kernel_param *kp;
 	struct module *mod;
 	long err = 0;
+#if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
+	void *refptr = NULL;
+#endif
 	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
 	unsigned long *mseg;
 	mm_segment_t old_fs;
@@ -2018,6 +2021,7 @@ static noinline struct module *load_module(void __user *umod,
 #if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
 	mod->refptr = percpu_modalloc(sizeof(local_t), __alignof__(local_t),
 				      mod->name);
+	refptr = mod->refptr;
 	if (!mod->refptr) {
 		err = -ENOMEM;
 		goto free_mod;
@@ -2292,10 +2296,14 @@ static noinline struct module *load_module(void __user *umod,
  free_core:
 	module_free(mod, mod->module_core);
  free_percpu:
+	/*
+	 * Do not access to mod anymore, it's now freed
+	 */
 	if (percpu)
 		percpu_modfree(percpu);
 #if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
-	percpu_modfree(mod->refptr);
+	if (refptr)
+		percpu_modfree(refptr);
 #endif
  free_mod:
 	kfree(args);

Re: [PATCH] module: fix refptr allocation and release order

[Rusty Russell]

On Tuesday 17 March 2009 13:54:36 Eric Dumazet wrote:
> Rusty Russell a écrit :
> > From: Masami Hiramatsu <mhiramat@redhat.com>
> > 
> > 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>
> 
> 
> My original patch did not have this problem, because I used a local variable
> to hold refptr.
> 
> http://www.archivum.info/linux-kernel@vger.kernel.org/2008-05/msg07400.html
> 
> A simpler patch could just use a local variable again, since we are very
> late in rc phase ?

Right, it was my mistake.  But the extra #ifdef is still ugly: moving the code
is a larger patch, but it's not complicated.

Thanks,
Rusty.