Re: [PATCH v5 00/11] vsprintf: Prevent silent crashes and consolidate error handling

From: Petr Mladek
Date: Fri Apr 27 2018 - 10:11:05 EST

On Wed 2018-04-25 13:12:40, Petr Mladek wrote:
> Crash in vsprintf() might be silent when it happens under logbuf_lock
> in vprintk_emit(). This patch set prevents most of the crashes by probing
> the address. The check is done only by %s and some %p* specifiers that need
> to dereference the address.
> Only the first byte of the address is checked to keep it simple. It should
> be enough to catch most problems.
> The check is explicitly done in each function that does the dereference.
> It helps to avoid the questionable strchr() of affected specifiers. This
> change motivated me to do some preparation patches that consolidated
> the error handling and cleaned the code a bit.
> I did my best to address the feedback. Note that there is still the
> (efault) error message. But it is accompanied with WARN() when
> panic_on_warn is not enabled. I hope that it makes it more acceptable.
> Changes against v4:
> + rebased on top of
> git:// for-4.18
> + Added missing conts into ptr_to_ind() in a separate patch
> + Renamed __string to valid_string()
> + Avoid WARN() for invalid poimter specifiers
> + Removed noinline_for_stack where it was not really useful
> + WARN() when accessing invalid non-NULL address

Thanks a lot everyone for feedback. I'll incorporate it into v6. It
might take some time.

BTW: I also got report from 0day robot about that the size of vmlinux
increased by 545 bytes in i386-tinyconfig. I guess that it is mainly
because all the copies of

if (!valid_pointer_access(&buf, end, bdev, spec))
return buf;

got inlined. I guess that I would need to address it somehow
as well.

Best Regards,