Re: [RFC][PATCH] printf: Harden accessing pointer dereference in vsprintf()

[Kees Cook]

On Mon, Jan 06, 2025 at 05:27:22PM -0500, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@xxxxxxxxxxx>
> 
> For extra safety from crashing the kernel, add a
> copy_from_kernel_nofault() in check_pointer_msg(). If it fails to read the
> memory, then return "(efault)".
> 
> This isn't full proof, as the length of the pointer being read could
> possibly go into bad memory, but this should catch the majority of errors.
> 
> Linus had suggested adding this kind of check[1]. This is a bit different
> than Linus's solution as it utilizes copy_from_kernel_nofault() and doesn't
> require calls to pagefault_disable() and extra labels.
> 
> [1] https://lore.kernel.org/all/CAHk-=wh3cUC2a=yJv42HTjDLCp6VM+GTky+q65vV_Q33BeoxAg@xxxxxxxxxxxxxx/
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>

Seems reasonable to me.

Reviewed-by: Kees Cook <kees@xxxxxxxxxx>

-Kees

-- 
Kees Cook