linux-kernel - Re: [PATCH] kprobes: fix out-of-bounds in register

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Date:   Wed, 1 Dec 2021 22:06:11 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     zhangyue <zhangyue1@...inos.cn>
Cc:     naveen.n.rao@...ux.ibm.com, anil.s.keshavamurthy@...el.com,
        davem@...emloft.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kprobes: fix out-of-bounds in register_kretprobe

On Wed,  1 Dec 2021 13:48:55 +0800
zhangyue <zhangyue1@...inos.cn> wrote:

> When the data 'rp->data_size' is negative, the code
> 'sizeof(struct kretprobe_instance)+rp->data_size'
> is less than 'sizeof(struct kretprobe_instance)'

Hmm, rp->data_size is size_t, which is unsigned value.
Of course we still need some kind of maximum limitation
because if we pass enough bigger size, the 
sizeof(struct kretprobe_instance) + rp->data_size
can be negative or smaller than sizeof(struct kretprobe_instance).

Thank you,

> 
> At this time, the pointer 'inst' may be out of
> bound when it is in use.
> 
> Signed-off-by: zhangyue <zhangyue1@...inos.cn>
> ---
>  kernel/kprobes.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 1cf8bca1ea86..71cf6bde299f 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1983,7 +1983,7 @@ int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long o
>  int register_kretprobe(struct kretprobe *rp)
>  {
>  	int ret;
> -	struct kretprobe_instance *inst;
> +	struct kretprobe_instance *inst = NULL;
>  	int i;
>  	void *addr;
>  
> @@ -2024,7 +2024,8 @@ int register_kretprobe(struct kretprobe *rp)
>  
>  	rp->rph->rp = rp;
>  	for (i = 0; i < rp->maxactive; i++) {
> -		inst = kzalloc(sizeof(struct kretprobe_instance) +
> +		if (rp->data_size >= 0)
> +			inst = kzalloc(sizeof(struct kretprobe_instance) +
>  			       rp->data_size, GFP_KERNEL);
>  		if (inst == NULL) {
>  			refcount_set(&rp->rph->ref, i);
> -- 
> 2.30.0
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>