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>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index f2b7c28a4708..af8c85664882 100644
--- 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);