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Date: Tue, 2 Feb 2021 18:23:26 +1100
From: Alexey Kardashevskiy <aik@...abs.ru>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Alexey Kardashevskiy <aik@...abs.ru>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Ingo Molnar <mingo@...hat.com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
linux-kernel@...r.kernel.org
Subject: [PATCH kernel] tracepoint: Fix race between tracing and removing tracepoint
When executing a tracepoint, the tracepoint's func is dereferenced twice -
in __DO_TRACE() (where the returned pointer is checked) and later on in
__traceiter_##_name where the returned pointer is dereferenced without
checking which leads to races against tracepoint_removal_sync() and
crashes.
This adds a check before referencing the pointer in tracepoint_ptr_deref.
Fixes: d25e37d89dd2f ("tracepoint: Optimize using static_call()")
Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
---
This is in reply to https://lkml.org/lkml/2021/2/1/868
Feel free to change the commit log. Thanks!
Fixing it properly is rather scary :)
I tried passing it_func_ptr to it_func but this change triggered way too
many prototypes changes such as __bpf_trace_##call().
---
include/linux/tracepoint.h | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 0f21617f1a66..966ed8980327 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -307,11 +307,13 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
\
it_func_ptr = \
rcu_dereference_raw((&__tracepoint_##_name)->funcs); \
- do { \
- it_func = (it_func_ptr)->func; \
- __data = (it_func_ptr)->data; \
- ((void(*)(void *, proto))(it_func))(__data, args); \
- } while ((++it_func_ptr)->func); \
+ if (it_func_ptr) { \
+ do { \
+ it_func = (it_func_ptr)->func; \
+ __data = (it_func_ptr)->data; \
+ ((void(*)(void *, proto))(it_func))(__data, args); \
+ } while ((++it_func_ptr)->func); \
+ } \
return 0; \
} \
DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);
--
2.17.1
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