Commit 2e8a12b8 authored Oct 31, 2024 by Mathieu Desnoyers Committed by Steven Rostedt (Google) Nov 01, 2024

tracing: Fix syscall tracepoint use-after-free



The grace period used internally within tracepoint.c:release_probes()
uses call_rcu() to batch waiting for quiescence of old probe arrays,
rather than using the tracepoint_synchronize_unregister() which blocks
while waiting for quiescence.

With the introduction of faultable syscall tracepoints, this causes
use-after-free issues reproduced with syzkaller.

Fix this by using the appropriate call_rcu() or call_rcu_tasks_trace()
before invoking the rcu_free_old_probes callback. This can be chosen
using the tracepoint_is_faultable() API.

A similar issue exists in bpf use of call_rcu(). Fixing this is left to
a separate change.

Reported-by:  <syzbot+b390c8062d8387b6272a@syzkaller.appspotmail.com>
Fixes: a363d27c ("tracing: Allow system call tracepoints to handle page faults")
Tested-by: Jordan Rife <jrife@google.com>
Cc: Michael Jeanson <mjeanson@efficios.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: bpf@vger.kernel.org
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Jordan Rife <jrife@google.com>
Cc: linux-trace-kernel@vger.kernel.org
Link: https://lore.kernel.org/20241031152056.744137-4-mathieu.desnoyers@efficios.com


Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

parent 654ced4a

kernel/tracepoint.c

+7 −4

Original line number	Diff line number	Diff line
		@@ -106,12 +106,15 @@ static void rcu_free_old_probes(struct rcu_head *head)
		kfree(container_of(head, struct tp_probes, rcu));
		}

		static inline void release_probes(struct tracepoint_func *old)
		static inline void release_probes(struct tracepoint tp, struct tracepoint_func old)
		{
		if (old) {
		struct tp_probes *tp_probes = container_of(old,
		struct tp_probes, probes[0]);

		if (tracepoint_is_faultable(tp))
		call_rcu_tasks_trace(&tp_probes->rcu, rcu_free_old_probes);
		else
		call_rcu(&tp_probes->rcu, rcu_free_old_probes);
		}
		}
		@@ -334,7 +337,7 @@ static int tracepoint_add_func(struct tracepoint *tp,
		break;
		}

		release_probes(old);
		release_probes(tp, old);
		return 0;
		}

		@@ -405,7 +408,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
		WARN_ON_ONCE(1);
		break;
		}
		release_probes(old);
		release_probes(tp, old);
		return 0;
		}