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.

Link: https://lkml.kernel.org/r/20210202072326.120557-1-aik@ozlabs.ru
Cc: stable@vger.kernel.org
Fixes: d25e37d89dd2f ("tracepoint: Optimize using static_call()")
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 0f21617..966ed89 100644 (file)
--- 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);