From: "Masami Hiramatsu (Google)" mhiramat@kernel.org

There is a small chance that get_kretprobe(ri) returns NULL in kretprobe_dispatcher() when another CPU unregisters the kretprobe right after __kretprobe_trampoline_handler().

To avoid this issue, kretprobe_dispatcher() checks the get_kretprobe() return value again. And if it is NULL, it returns soon because that kretprobe is under unregistering process.

This issue has been introduced when the kretprobe is decoupled from the struct kretprobe_instance by commit d741bf41d7c7 ("kprobes: Remove kretprobe hash"). Before that commit, the struct kretprob_instance::rp directly points the kretprobe and it is never be NULL.

Link: https://lkml.kernel.org/r/165366693881.797669.16926184644089588731.stgit@dev...

Reported-by: Yonghong Song yhs@fb.com Fixes: d741bf41d7c7 ("kprobes: Remove kretprobe hash") Cc: Peter Zijlstra peterz@infradead.org Cc: Ingo Molnar mingo@kernel.org Cc: bpf bpf@vger.kernel.org Cc: Kernel Team kernel-team@fb.com Cc: stable@vger.kernel.org Signed-off-by: Masami Hiramatsu (Google) mhiramat@kernel.org Acked-by: Jiri Olsa jolsa@kernel.org Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- kernel/trace/trace_kprobe.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c index 93507330462c..a245ea673715 100644 --- a/kernel/trace/trace_kprobe.c +++ b/kernel/trace/trace_kprobe.c @@ -1718,8 +1718,17 @@ static int kretprobe_dispatcher(struct kretprobe_instance *ri, struct pt_regs *regs) { struct kretprobe *rp = get_kretprobe(ri); - struct trace_kprobe *tk = container_of(rp, struct trace_kprobe, rp); + struct trace_kprobe *tk; + + /* + * There is a small chance that get_kretprobe(ri) returns NULL when + * the kretprobe is unregister on another CPU between kretprobe's + * trampoline_handler and this function. + */ + if (unlikely(!rp)) + return 0;

+ tk = container_of(rp, struct trace_kprobe, rp); raw_cpu_inc(*tk->nhit);

if (trace_probe_test_flag(&tk->tp, TP_FLAG_TRACE))