Re: [PATCH] kprobes: Fix NULL pointer dereference in unregister_kretprobes()

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Wed,  5 Aug 2026 16:12:21 +0000
Luigi Rizzo <lrizzo@google.com> wrote:

> In unregister_kretprobes(), rps[i]->rph can be NULL e.g. when called
> after kretprobe failed registration. Under !CONFIG_KRETPROBE_ON_RETHOOK,
> the unconditional access to rps[i]->rph->rp, causes a kernel panic due
> to NULL pointer dereference.

This is not a bug, since if register_kretprobe(rp) fails, rp must NOT be
passed to unregister_kretprobe(rp). Or, do you find any cases where
register_kretprobe() fails, preventing proper cleanup, and requiring
unregister_kretprobe()? If so, we have to fix that case.

> 
> Add a NULL check for rps[i]->rph before invoking rcu_assign_pointer().
> 

But this could be a kind of protective improvemet for someone
misunderstand that.

Thank you,

> Fixes: d839a656d0f3 ("kprobes: consistent rcu api usage for kretprobe holder")
> Signed-off-by: Luigi Rizzo <lrizzo@google.com>
> ---
>  kernel/kprobes.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index bfc89083daa93..5dd4786c455de 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2359,7 +2359,8 @@ void unregister_kretprobes(struct kretprobe **rps, int num)
>  #ifdef CONFIG_KRETPROBE_ON_RETHOOK
>  		rethook_free(rps[i]->rh);
>  #else
> -		rcu_assign_pointer(rps[i]->rph->rp, NULL);
> +		if (rps[i]->rph)
> +			rcu_assign_pointer(rps[i]->rph->rp, NULL);
>  #endif
>  	}
>  
> -- 
> 2.48.1.500.g5897711438-goog
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>