linux-kernel - [RFC PATCH v3 3/3] tracing: Fix syscall tracepoint use-after-free

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Message-Id: <20241026154629.593041-3-mathieu.desnoyers@efficios.com>
Date: Sat, 26 Oct 2024 11:46:29 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Michael Jeanson <mjeanson@...icios.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Yonghong Song <yhs@...com>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	bpf@...r.kernel.org,
	Joel Fernandes <joel@...lfernandes.org>,
	Jordan Rife <jrife@...gle.com>,
	syzbot+b390c8062d8387b6272a@...kaller.appspotmail.com
Subject: [RFC PATCH v3 3/3] 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_syscall() API.

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

Reported-by: syzbot+b390c8062d8387b6272a@...kaller.appspotmail.com
Fixes: a363d27cdbc2 ("tracing: Allow system call tracepoints to handle page faults")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Michael Jeanson <mjeanson@...icios.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Yonghong Song <yhs@...com>
Cc: Paul E. McKenney <paulmck@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: bpf@...r.kernel.org
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Jordan Rife <jrife@...gle.com>
---
Changes since v0:
- Introduce tracepoint_call_rcu(),
- Fix bpf_link_free() use of call_rcu as well.

Changes since v1:
- Use tracepoint_call_rcu() for bpf_prog_put as well.

Changes since v2:
- Do not cover bpf changes in the same commit, let bpf developers
  implement it.
---
 kernel/tracepoint.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 5658dc92f5b5..47569fb06596 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -106,13 +106,16 @@ 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]);
 
-		call_rcu(&tp_probes->rcu, rcu_free_old_probes);
+		if (tracepoint_is_syscall(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;
 }
 
-- 
2.39.5