Re: [RFC PATCH 06/20] rv: Add rv_get_monitor_by_name()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] rv_is_container_monitor() fails to identify an empty container if it is the last element in the list, leading to a NULL pointer dereference when enabled.
--

commit a8e1e1f414fc69c200ed8ba3fee4d10346fe86df
Author: Gabriele Monaco <gmonaco@redhat.com>

rv: Add rv_get_monitor_by_name()
    
Add a helper function to get the rv_monitor pointer for a registered
monitor given its name and add its first user in rv_register_monitor().

> diff --git a/kernel/trace/rv/rv.c b/kernel/trace/rv/rv.c
> index f77c5865f41ab..33919c5fbd6ad 100644
> --- a/kernel/trace/rv/rv.c
> +++ b/kernel/trace/rv/rv.c
[ ... ]
> @@ -229,6 +230,18 @@ bool rv_is_container_monitor(struct rv_monitor *mon)
>  	return next->parent == mon || !mon->enable;
>  }

[Severity: High]
This isn't a bug introduced by this patch, but there is a pre-existing
issue in rv_is_container_monitor(). Does this function incorrectly classify
an empty container monitor if it happens to be the last element in
rv_monitors_list?

Looking at the rest of rv_is_container_monitor():

bool rv_is_container_monitor(struct rv_monitor *mon)
{
	...
	if (list_is_last(&mon->list, &rv_monitors_list))
		return false;

	next = list_next_entry(mon, list);
	return next->parent == mon || !mon->enable;
}

If an empty container monitor (which has a NULL enable function) is the last
element, it returns false early. This bypasses the !mon->enable check,
treating the empty container as a regular monitor.

If a user then writes to its tracefs enable file, rv_enable_single() appears
to unconditionally call the enable function:

	retval = mon->enable();

Since the empty container monitor has a NULL enable pointer, will this lead
to a kernel panic via a NULL pointer dereference when enabled?

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260831090524.106845-1-gmonaco@redhat.com?part=6