Re: [PATCH] x86/kprobes: Fix KRETPROBES when CONFIG_KRETPROBE_ON_RETHOOK is set

[Masami Hiramatsu <mhiramat@kernel.org>]

On Fri, 15 Apr 2022 20:10:06 +0200
Adam Zabrocki <pi3@pi3.com.pl> wrote:

> [PATCH] x86/kprobes: Fix KRETPROBES when CONFIG_KRETPROBE_ON_RETHOOK is set
> 
> The recent kernel change "kprobes: Use rethook for kretprobe if possible",
> introduced a potential NULL pointer dereference bug in the KRETPROBE
> mechanism. The official Kprobes documentation defines that "Any or all
> handlers can be NULL". Unfortunately, there is a missing return handler
> verification to fulfill these requirements and can result in a NULL pointer
> dereference bug.
> 
> This patch adds such verification in kretprobe_rethook_handler() function.
> 

Good catch! I forgot that user can register kretprobe without handler...

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thank you!

> Fixes: 73f9b911faa7 ("kprobes: Use rethook for kretprobe if possible")
> Signed-off-by: Adam Zabrocki <pi3@pi3.com.pl>
> ---
>  kernel/kprobes.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index dbe57df2e199..dd58c0be9ce2 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2126,7 +2126,7 @@ static void kretprobe_rethook_handler(struct rethook_node *rh, void *data,
>  	struct kprobe_ctlblk *kcb;
>  
>  	/* The data must NOT be null. This means rethook data structure is broken. */
> -	if (WARN_ON_ONCE(!data))
> +	if (WARN_ON_ONCE(!data) || !rp->handler)
>  		return;
>  
>  	__this_cpu_write(current_kprobe, &rp->kp);
> 
> -- 
> pi3 (pi3ki31ny) - pi3 (at) itsec pl
> http://pi3.com.pl
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>