On Wed, Jul 27, 2022 at 6:17 PM Alexey Khoroshilov
<khoroshilov@xxxxxxxxx> wrote:
> On 01.10.2021 22:59, Linus Torvalds wrote:
> Coming back to the discussion of WARN_ON()/pr_warn("WARNING:") semantics.
>
> We see a number of cases where WARNING is used to inform userspace that
> it is doing something wrong, e.g.
> https://elixir.bootlin.com/linux/v5.19-rc8/source/net/can/j1939/socket.c#L181
> https://elixir.bootlin.com/linux/v5.19-rc8/source/drivers/video/fbdev/core/fbmem.c#L1023
>
> It is definitely useful, but it does not make sense in case of fuzzing
> when the userspace should do wrong things and check if kernel behaves
> correctly.
>
> As a result we have warnings with two different intentions:
> - warn that something wrong happens in kernel, but we are able to continue;
> - warn userspace that it is doing something wrong.
>
> During fuzzing we would like to report the former and to ignore the
> latter. Are any ideas how these intentions can be recognized automatically?
https://elixir.bootlin.com/linux/v5.19-rc8/source/include/asm-generic/bug.h#L74
says:
* WARN(), WARN_ON(), WARN_ON_ONCE, and so on can be used to report
* significant kernel issues that need prompt attention if they should ever
* appear at runtime.
*
* Do not use these macros when checking for invalid external inputs
* (e.g. invalid system call arguments, or invalid data coming from
* network/devices), and on transient conditions like ENOMEM or EAGAIN.
* These macros should be used for recoverable kernel issues only.
* For invalid external inputs, transient conditions, etc use
* pr_err[_once/_ratelimited]() followed by dump_stack(), if necessary.
* Do not include "BUG"/"WARNING" in format strings manually to make these
* conditions distinguishable from kernel issues.
So if you see drivers intentionally using WARN() or printing
"WARNING:" on codepaths that are reachable with bogus inputs from
userspace, those codepaths should be fixed to log warnings in a
different format.
