tracepoint: check if the probe has been registered

Impact: fix kernel crash that can trigger during tracing

If we try to remove a probe that has not been already registered,
the tracepoint_entry_remove_probe() function will dereference a NULL
pointer.

Check the probe before removing it to avoid crashes.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index f2b7c28..af8c856 100644 (file)
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -131,6 +131,9 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe)
 
        old = entry->funcs;
 
+       if (!old)
+               return NULL;
+
        debug_print_probes(entry);
        /* (N -> M), (N > 1, M >= 0) probes */
        for (nr_probes = 0; old[nr_probes]; nr_probes++) {
@@ -388,6 +391,11 @@ int tracepoint_probe_unregister(const char *name, void *probe)
        if (entry->rcu_pending)
                rcu_barrier_sched();
        old = tracepoint_entry_remove_probe(entry, probe);
+       if (!old) {
+               printk(KERN_WARNING "Warning: Trying to unregister a probe"
+                                   "that doesn't exist\n");
+               goto end;
+       }
        mutex_unlock(&tracepoints_mutex);
        tracepoint_update_probes();             /* may update entry */
        mutex_lock(&tracepoints_mutex);