Messages in this thread | | | Subject | Re: [PATCH 0/2] tracing: Fix NULL pointer bug in hist key expressions | From | Tom Zanussi <> | Date | Thu, 08 Nov 2018 13:12:33 -0600 |
| |
Hi Steve,
On Thu, 2018-11-08 at 13:45 -0500, Steven Rostedt wrote: > On Thu, 8 Nov 2018 08:41:47 -0600 > Tom Zanussi <zanussi@kernel.org> wrote: > > > From: Tom Zanussi <tom.zanussi@linux.intel.com> > > > > 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? >
Sure, here's the example that showed the problem, and which the patch fixes:
echo 'r:fib_table_lookup_ret fib_table_lookup $retval' > /sys/kernel/debug/tracing/kprobe_events
echo 'hist:keys=cpu:ts0=common_timestamp' > /sys/kernel/debug/tracing/events/fib/fib_table_lookup/trigger echo 'hist:keys=cpu,common_timestamp-$ts0' > /sys/kernel/debug/tracing/events/kprobes/fib_table_lookup_ret/trigger
The following is also a variable reference in an expression, but in this case the expression is the variable reference alone, which the existing code handles properly and returns -EINVAL.
echo 'hist:keys=cpu,$ts0' > /sys/kernel/debug/tracing/events/kprobes/fib_table_lookup_ret/trigger
Tom
> -- 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(-) > > > >
| |