Re: [PATCH] kprobes: Limit max data_size of the kretprobe instances

[Masami Hiramatsu]

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

> On Wed,  1 Dec 2021 23:45:50 +0900
> Masami Hiramatsu <mhiramat@xxxxxxxxxx> 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@xxxxxxxxxx>