linux-kernel - Re: [PATCH] kprobes: Limit max data

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Message-Id: <20211202091344.f9725841b0cf704b9342b5f2@kernel.org>
Date:   Thu, 2 Dec 2021 09:13:44 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        zhangyue <zhangyue1@...inos.cn>, naveen.n.rao@...ux.ibm.com,
        anil.s.keshavamurthy@...el.com, davem@...emloft.net
Subject: Re: [PATCH] kprobes: Limit max data_size of the kretprobe instances

On Wed, 1 Dec 2021 11:19:22 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed,  1 Dec 2021 23:45:50 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > The kretprobe::data_size is unsigned (size_t) but it is
> > used as 'data_size + sizeof(struct kretprobe_instance)'.
> > Thus, it can be smaller than sizeof(struct kretprobe_instance)
> > while allocating memory for the kretprobe_instance.
> 
> The above doesn't make sense.
> 
> data_size is unsigned but it is used as
>  'data_size + sizeof(struct kretprobe_instance)'. 
> 
> What does that mean?
> 
> What can be smaller than sizeof(struct kretprobe_instance) and why does it
> matter?

OK, what about this ?

The 'kprobe::data_size' is unsigned, thus it can not be negative.
But if user sets it enough big number (e.g. (size_t)-8), the result
of 'data_size + sizeof(struct kretprobe_instance)' becomes smaller than
sizeof(struct kretprobe_instance) or zero. In result, the kretprobe_instance
are allocated without enough memory, and kretprobe accesses outside of
allocated memory.

Thank you,

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