linux-kernel - Re: [PATCHv3 bpf-next 5/8] ftrace: Add update_ftrace_direct

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Message-ID: <aSBuv8Ab0y8SeAHS@krava>
Date: Fri, 21 Nov 2025 14:53:03 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: bot+bpf-ci@...nel.org
Cc: rostedt@...nel.org, revest@...gle.com, mark.rutland@....com,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, ast@...nel.org,
	daniel@...earbox.net, andrii@...nel.org, menglong8.dong@...il.com,
	song@...nel.org, martin.lau@...nel.org, eddyz87@...il.com,
	yonghong.song@...ux.dev, clm@...a.com, ihor.solodrai@...ux.dev
Subject: Re: [PATCHv3 bpf-next 5/8] ftrace: Add update_ftrace_direct_mod
 function

On Thu, Nov 20, 2025 at 10:23:47PM +0000, bot+bpf-ci@...nel.org wrote:
> > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> > index c571deeff..4e2c0ed76 100644
> > --- a/include/linux/ftrace.h
> > +++ b/include/linux/ftrace.h
> 
> [ ... ]
> 
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index cc730a8fd..5243aefb6 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> 
> [ ... ]
> 
> > @@ -6486,6 +6486,74 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
> >  	return err;
> >  }
> >
> > +int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock)
> > +{
> > +	struct ftrace_hash *orig_hash = ops->func_hash->filter_hash;
>                                              ^^^^^^^^^^^^^^^^
> 
> Can this crash if ops->func_hash is NULL?  In update_ftrace_direct_add()
> and update_ftrace_direct_del(), there's a defensive check:
> 
>     old_filter_hash = ops->func_hash ? ops->func_hash->filter_hash : NULL;
> 
> But update_ftrace_direct_mod() dereferences ops->func_hash before any
> validation checks occur. The check_direct_multi(ops) validation happens
> later, but the dereference occurs first at function entry.

update_ftrace_direct_add is called before update_ftrace_direct_mod which
ensures the existence of the filter_hash, but same as for the update_ftrace_direct_del
case in the other reply, it's probably better to add the check for future

thanks,
jirka


> 
> > +	struct ftrace_func_entry *entry, *tmp;
> > +	static struct ftrace_ops tmp_ops = {
> > +		.func		= ftrace_stub,
> > +		.flags		= FTRACE_OPS_FL_STUB,
> > +	};
> > +	unsigned long size, i;
> > +	int err;
> > +
> > +	if (!hash_count(hash))
> > +		return -EINVAL;
> > +	if (check_direct_multi(ops))
> > +		return -EINVAL;
> 
> [ ... ]
> 
> 
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
> 
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/19552032346