Re: [PATCH 0/2] tracing: Fix NULL pointer bug in hist key expressions

[Steven Rostedt]

On Thu,  8 Nov 2018 08:41:47 -0600
Tom Zanussi <zanussi@xxxxxxxxxx> wrote:

> From: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
> 
> Hi Steve,
> 
> This is a fix for a user-reported bug in the hist triggers, where if a
> variable reference is used in an expression in a histogram key, it
> results in a NULL pointer dereference and subsequent Oops.

How does one add a variable reference as an expression in a
histogram key?

Can you show an example?

-- Steve

> 
> I separated the fix into two small patches, the first preventing the
> immediate problem bu disallowing a var_ref from ever accessing a NULL
> element, and the second disallowing a user from ever constructing such
> a key.
> 
> Thanks,
> 
> Tom
> 
> The following changes since commit ee474b81fe5aa5dc0faae920bf66240fbf55f891:
> 
>   tracing/kprobes: Fix strpbrk() argument order (2018-11-05 09:47:14 -0500)
> 
> are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/zanussi/linux-trace.git ftrace/key-ref-fix
> 
> Tom Zanussi (2):
>   tracing: Prevent hist_field_var_ref() from accessing NULL
>     tracing_map_elts
>   tracing: Check keys for variable references in expressions too
> 
>  kernel/trace/trace_events_hist.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>