Re: [PATCH] static_call: fix null-ptr-deref in static_call_del_module

[wanghai (M)]

在 2021/10/9 18:00, Peter Zijlstra 写道:
> On Sat, Oct 09, 2021 at 03:44:28PM +0800, Wang Hai wrote:
> > I got a NULL pointer dereference report when doing fault injection test:
> >
> > BUG: kernel NULL pointer dereference, address: 0000000000000009
> > ...
> > RIP: 0010:static_call_del_module+0x7a/0x100
> > ...
> > Call Trace:
> >   static_call_module_notify+0x1e1/0x200
> >   notifier_call_chain_robust+0x6f/0xe0
> >   blocking_notifier_call_chain_robust+0x4e/0x70
> >   load_module+0x21f7/0x2b60
> >   __do_sys_finit_module+0xb0/0xf0
> >   ? __do_sys_finit_module+0xb0/0xf0
> >   __x64_sys_finit_module+0x1a/0x20
> >   do_syscall_64+0x34/0xb0
> >   entry_SYSCALL_64_after_hwframe+0x44/0xae
> >
> > When loading a module, if it fails to allocate memory for static
> > calls, it will delete the non-existent mods (mods == 1) in the
> > static_call_module_notify()'s error path.
> >
> > static_call_module_notify
> > 	static_call_add_module
> > 		__static_call_init
> > 			site_mod = kzalloc() // fault injection
> > 	static_call_del_module // access non-existent mods
> >
> > This patch fixes the bug by skipping the operation when the key
> > has no mods.
> >
> > Fixes: a945c8345ec0 ("static_call: Allow early init")
> > Signed-off-by: Wang Hai <wanghai38@xxxxxxxxxx>
> > ---
> >   kernel/static_call.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/static_call.c b/kernel/static_call.c
> > index 43ba0b1e0edb..c3f8ffc5a52f 100644
> > --- a/kernel/static_call.c
> > +++ b/kernel/static_call.c
> > @@ -400,7 +400,7 @@ static void static_call_del_module(struct module *mod)
> >   
> >   	for (site = start; site < stop; site++) {
> >   		key = static_call_key(site);
> > -		if (key == prev_key)
> > +		if (key == prev_key || !static_call_key_has_mods(key))
> >   			continue;
> >   
> >   		prev_key = key;
> Should you not update prev_key in that case? Also have you looked at
> jump_label_del_module() which is very similar in construction?
> .
Thanks for your guidance, as with jump_label_del_module(),
the prev_key needs to be updated, can it be fixed like this?

--- a/kernel/static_call.c
+++ b/kernel/static_call.c
@@ -404,9 +404,9 @@ static void static_call_del_module(struct module *mod)
                        continue;

                prev_key = key;
+               site_mod = static_call_key_next(key);

-               for (prev = &key->mods, site_mod = key->mods;
-                    site_mod && site_mod->mod != mod;
+               for (prev = &key->mods; site_mod && site_mod->mod != mod;
                     prev = &site_mod->next, site_mod = site_mod->next)
                        ;

--
Wang Hai