On Fri, 23 May 2025 16:39:44 +0800
Ye Bin <ye...@huaweicloud.com> wrote:
> Above issue may happens as follow:
> (1) Add kprobe trace point;
> (2) insmod test.ko;
> (3) Trigger ftrace disabled;
This is the bug. How was ftrace_disabled triggered? That should never
happen. Was test.ko buggy?
> (4) rmmod test.ko;
> (5) cat /proc/kallsyms; --> Will trigger UAF as test.ko already removed;
> ftrace_mod_get_kallsym()
> ...
> strscpy(module_name, mod_map->mod->name, MODULE_NAME_LEN);
> ...
>
> As ftrace_release_mod() judge 'ftrace_disabled' is true will return, and
> 'mod_map' will remaining in ftrace_mod_maps. 'mod_map' has no chance to
> release. Therefore, this also causes residual resources to accumulate.
> To solve above issue, unconditionally clean up'mod_map'.
>
> Fixes: aba4b5c22cba ("ftrace: Save module init functions kallsyms symbols for
> tracing")
This is *not* a fix. ftrace_disabled gets set when a bug is triggered. If
this prevents ftrace_disabled from getting set, then it would be a fix. But
if something else happens when ftrace_disabled is set, it just fixes a
symptom and not the bug itself.
> Signed-off-by: Ye Bin <yebi...@huawei.com>
> ---
> kernel/trace/ftrace.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index a3d4dfad0cbc..ff5d9d73a4a7 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -7438,9 +7438,6 @@ void ftrace_release_mod(struct module *mod)
>
> mutex_lock(&ftrace_lock);
>
> - if (ftrace_disabled)
> - goto out_unlock;
> -
Here you delete the check, and the next patch you have:
+ if (ftrace_disabled || (mod && !mod->num_ftrace_callsites)) {
+ mutex_unlock(&ftrace_lock);
+ return;
+ }
+
Why the two patches where the second patch just adds back the check and
then adds some more stuff around it. This should be a single patch.
Also, why not just keep the goto unlock, that has:
out_unlock:
mutex_unlock(&ftrace_lock);
/* Need to synchronize with ftrace_location_range() */
if (tmp_page)
synchronize_rcu();
for (pg = tmp_page; pg; pg = tmp_page) {
/* Needs to be called outside of ftrace_lock */
clear_mod_from_hashes(pg);
if (pg->records) {
free_pages((unsigned long)pg->records, pg->order);
ftrace_number_of_pages -= 1 << pg->order;
}
tmp_page = pg->next;
kfree(pg);
ftrace_number_of_groups--;
}
}
And tmp_page is set to NULL before that jump, so the if and for loop will
both be nops.
Why all this extra churn?
-- Steve
> list_for_each_entry_safe(mod_map, n, &ftrace_mod_maps, list) {
> if (mod_map->mod == mod) {
> list_del_rcu(&mod_map->list);
