From: Qing Wang <wangqing7171@gmail.com>
To: Song Liu <song@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
peterz@infradead.org, acme@kernel.org,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@fomichev.me>, Hao Luo <haoluo@google.com>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-perf-users@vger.kernel.org,
Qing Wang <wangqing7171@gmail.com>,
syzbot+72a43cdb78469f7fbad1@syzkaller.appspotmail.com
Subject: [PATCH] bpf/perf: Fix suspicious RCU usage in get_callchain_entry()
Date: Wed, 28 Jan 2026 14:17:53 +0800 [thread overview]
Message-ID: <20260128061753.1857803-1-wangqing7171@gmail.com> (raw)
There is a patch intended to fix suspicious RCU usage in get_callchain_entry(),
but it is incorrect. Specifically, rcu_read_lock()/rcu_read_unlock() is not
called when may_fault == false.
Previous discussion:
https://lore.kernel.org/all/CAEf4BzaYL9zZN8TZyRHW3_O3vbHc7On+NSunrkDvDQx2=wwyRw@mail.gmail.com/#R
For perf's callchain, rcu_read_lock()/rcu_read_unlock() should be called when
trace_in == false.
Fixes: d4dd9775ec24 ("bpf: wire up sleepable bpf_get_stack() and bpf_get_task_stack() helpers")
Reported-by: syzbot+72a43cdb78469f7fbad1@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=72a43cdb78469f7fbad1
Tested-by: syzbot+72a43cdb78469f7fbad1@syzkaller.appspotmail.com
Signed-off-by: Qing Wang <wangqing7171@gmail.com>
---
kernel/bpf/stackmap.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index da3d328f5c15..f97d4aa9d038 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -460,7 +460,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
max_depth = stack_map_calculate_max_depth(size, elem_size, flags);
- if (may_fault)
+ if (!trace_in)
rcu_read_lock(); /* need RCU for perf's callchain below */
if (trace_in) {
@@ -474,7 +474,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
}
if (unlikely(!trace) || trace->nr < skip) {
- if (may_fault)
+ if (!trace_in)
rcu_read_unlock();
goto err_fault;
}
@@ -494,7 +494,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
}
/* trace/ips should not be dereferenced after this point */
- if (may_fault)
+ if (!trace_in)
rcu_read_unlock();
if (user_build_id)
--
2.34.1
next reply other threads:[~2026-01-28 6:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-28 6:17 Qing Wang [this message]
2026-02-04 0:04 ` [PATCH] bpf/perf: Fix suspicious RCU usage in get_callchain_entry() Andrii Nakryiko
2026-02-04 9:14 ` Qing Wang
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