Subject: Re: [PATCH] kallsyms: don't leak address when printing symbol

From: Steven Rostedt <[email-masked]>
Date: Wed, 8 Nov 2017 22:35:55 -0500

On Thu,  9 Nov 2017 12:50:29 +1100
"Tobin C. Harding" <[email-masked]> wrote:

> Currently if a pointer is printed using %p[ssB] and the symbol is not
> found (kallsyms_lookup() fails) then we print the actual address. This
> leaks kernel addresses. We should instead print something _safe_.
> 
> Print "<no-symbol>" instead of kernel address.

Ug, ftrace requires this to work as is, as it uses it to print some
addresses that may or may not be a symbol.

If anything, can this return a success or failure if it were to find a
symbol or not, and then something like ftrace could decide to use %x if
it does not.

And yes, ftrace leaks kernel addresses all over the place, that's just
the nature of tracing the kernel.

-- Steve

> 
> Signed-off-by: Tobin C. Harding <[email-masked]>
> ---
>  kernel/kallsyms.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 127e7cfafa55..182e7592be9c 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -390,7 +390,7 @@ static int __sprint_symbol(char *buffer, unsigned long address,
>  	address += symbol_offset;
>  	name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
>  	if (!name)
> -		return sprintf(buffer, "0x%lx", address - symbol_offset);
> +		return sprintf(buffer, "<no-symbol>");
>  
>  	if (name != buffer)
>  		strcpy(buffer, name);