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

[JP Kobryn <inwardvessel@gmail.com>]

On 8/5/2026 9:12 AM, Luigi Rizzo 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.
> 
> Add a NULL check for rps[i]->rph before invoking rcu_assign_pointer().
> 
> Fixes: d839a656d0f3 ("kprobes: consistent rcu api usage for kretprobe holder")

The bug was not introduced in this commit. It goes further back to:

d741bf41d7c7 ("kprobes: Remove kretprobe hash")

> 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
>   	}
>