Re: [PATCH v2] module: print version for external modules in print_modules()

[Sami Tolvanen <samitolvanen@google.com>]

On Wed, Dec 31, 2025 at 05:40:04PM +0800, Yafang Shao wrote:
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -3901,7 +3901,11 @@ void print_modules(void)
>  	list_for_each_entry_rcu(mod, &modules, list) {
>  		if (mod->state == MODULE_STATE_UNFORMED)
>  			continue;
> -		pr_cont(" %s%s", mod->name, module_flags(mod, buf, true));
> +		pr_cont(" %s", mod->name);
> +		/* Only append version for out-of-tree modules */
> +		if (mod->version && test_bit(TAINT_OOT_MODULE, &mod->taints))
> +			pr_cont("-%s", mod->version);
> +		pr_cont("%s", module_flags(mod, buf, true));

On second thought, is using mod->version here safe? We release the
memory for mod->version in:

  free_module
    -> mod_sysfs_teardown
    -> module_remove_modinfo_attrs
    -> attr->free = free_modinfo_version

And this happens before the module is removed from the
list. Couldn't there be a race condition where we read a non-NULL
mod->version here, but the buffer is being concurrently released
by another core that's unloading the module, resulting in a
use-after-free in the pr_cont call?

In order to do this safely, we should presumably drop the attr->free
call from module_remove_modinfo_attrs and release the attributes
only after the synchronize_rcu call in free_module (there's already
free_modinfo we can use), so mod->version is valid for the entire
time the module is on the list.

Thoughts?

Sami