linux-hardening - Re: splat in ikheaders

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Date:   Thu, 2 Mar 2023 14:12:31 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Kees Cook <kees@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>, linux-hardening@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: splat in ikheaders_read (bpftrace)

On Thu, 2 Mar 2023 14:08:14 -0800 Jakub Kicinski wrote:
> > static ssize_t
> > ikheaders_read(struct file *file,  struct kobject *kobj,
> > 	       struct bin_attribute *bin_attr,
> > 	       char *buf, loff_t off, size_t len)
> > {
> > 	memcpy(buf, &kernel_headers_data + off, len);
> > 	return len;
> > }
> > 
> > I will take a look at the caller's allocation of "buf" and kernel_headers_data.  
> 
> Mm. Actually stopping to look at the code - I don't see it bound
> checking against kernel_headers_data_end :| Maybe we need:
> 
> @@ -34,6 +35,7 @@ ikheaders_read(struct file *file,  struct kobject *kobj,
>                struct bin_attribute *bin_attr,
>                char *buf, loff_t off, size_t len)
>  {
> +       len = min_t(size_t, kernel_headers_data_end - kernel_headers_data, len);
>         memcpy(buf, &kernel_headers_data + off, len);
>         return len;
>  }

Scratch that, the size is set at init time.
My guess was memcpy() thinks the size of kernel_headers_data
is 1 since it's declared as char?