tracepoint: Fix use of tracepoint funcs after rcu free

Commit de7b2973903c "tracepoint: Use struct pointer instead of name hash
for reg/unreg tracepoints" introduces a use after free by calling
release_probes on the old struct tracepoint array before the newly
allocated array is published with rcu_assign_pointer. There is a race
window where tracepoints (RCU readers) can perform a
"use-after-grace-period-after-free", which shows up as a GPF in
stress-tests.

Link: http://lkml.kernel.org/r/53698021.5020108@oracle.com
Link: http://lkml.kernel.org/p/1399549669-25465-1-git-send-email-mathieu.desnoyers@efficios.com
Reported-by: Sasha Levin <sasha.levin@oracle.com>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Dave Jones <davej@redhat.com>
Fixes: de7b2973903c "tracepoint: Use struct pointer instead of name hash for reg/unreg tracepoints"
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index ac5b23c..6620e58 100644 (file)
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -188,7 +188,6 @@ static int tracepoint_add_func(struct tracepoint *tp,
                WARN_ON_ONCE(1);
                return PTR_ERR(old);
        }
-       release_probes(old);
 
        /*
         * rcu_assign_pointer has a smp_wmb() which makes sure that the new
@@ -200,6 +199,7 @@ static int tracepoint_add_func(struct tracepoint *tp,
        rcu_assign_pointer(tp->funcs, tp_funcs);
        if (!static_key_enabled(&tp->key))
                static_key_slow_inc(&tp->key);
+       release_probes(old);
        return 0;
 }
 
@@ -221,7 +221,6 @@ static int tracepoint_remove_func(struct tracepoint *tp,
                WARN_ON_ONCE(1);
                return PTR_ERR(old);
        }
-       release_probes(old);
 
        if (!tp_funcs) {
                /* Removed last function */
@@ -232,6 +231,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
                        static_key_slow_dec(&tp->key);
        }
        rcu_assign_pointer(tp->funcs, tp_funcs);
+       release_probes(old);
        return 0;
 }