Commit c0f3bb40 authored Jun 08, 2022 by Masami Hiramatsu (Google) Committed by Daniel Borkmann Jun 17, 2022

rethook: Reject getting a rethook if RCU is not watching



Since the rethook_recycle() will involve the call_rcu() for reclaiming
the rethook_instance, the rethook must be set up at the RCU available
context (non idle). This rethook_recycle() in the rethook trampoline
handler is inevitable, thus the RCU available check must be done before
setting the rethook trampoline.

This adds a rcu_is_watching() check in the rethook_try_get() so that
it will return NULL if it is called when !rcu_is_watching().

Fixes: 54ecbe6f ("rethook: Add a generic return hook")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/165461827269.280167.7379263615545598958.stgit@devnote2

parent c88dbbcd

kernel/trace/rethook.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -154,6 +154,15 @@ struct rethook_node rethook_try_get(struct rethook rh)
		if (unlikely(!handler))
		return NULL;

		/*
		* This expects the caller will set up a rethook on a function entry.
		* When the function returns, the rethook will eventually be reclaimed
		* or released in the rethook_recycle() with call_rcu().
		* This means the caller must be run in the RCU-availabe context.
		*/
		if (unlikely(!rcu_is_watching()))
		return NULL;

		fn = freelist_try_get(&rh->pool);
		if (!fn)
		return NULL;