Fix: enable event error path memory corruption

The call to

  kmem_cache_free(event_cache, event);

after setting event to ERR_PTR() value is causing memory corruption
(kernel oops). This bug has been introduced very recently by commit:

  Fix: provide more precise error report for enable event

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/lttng-events.c b/lttng-events.c
index 09729bcff20f0ca1dd1c4d9ff9eaa8035ec15dcb..c1b3b44d4af7be7270e98929fb72688eab3073df 100644 (file)
--- a/lttng-events.c
+++ b/lttng-events.c
@@ -368,7 +368,7 @@ struct lttng_event *lttng_event_create(struct lttng_channel *chan,
 
        mutex_lock(&sessions_mutex);
        if (chan->free_event_id == -1U) {
-               event = ERR_PTR(-EMFILE);
+               ret = -EMFILE;
                goto full;
        }
        /*
@@ -377,13 +377,13 @@ struct lttng_event *lttng_event_create(struct lttng_channel *chan,
         */
        list_for_each_entry(event, &chan->session->events, list) {
                if (!strcmp(event->desc->name, event_param->name)) {
-                       event = ERR_PTR(-EEXIST);
+                       ret = -EEXIST;
                        goto exist;
                }
        }
        event = kmem_cache_zalloc(event_cache, GFP_KERNEL);
        if (!event) {
-               event = ERR_PTR(-ENOMEM);
+               ret = -ENOMEM;
                goto cache_error;
        }
        event->chan = chan;
@@ -397,14 +397,14 @@ struct lttng_event *lttng_event_create(struct lttng_channel *chan,
        case LTTNG_KERNEL_TRACEPOINT:
                event->desc = lttng_event_get(event_param->name);
                if (!event->desc) {
-                       event = ERR_PTR(-ENOENT);
+                       ret = -ENOENT;
                        goto register_error;
                }
                ret = kabi_2635_tracepoint_probe_register(event_param->name,
                                event->desc->probe_callback,
                                event);
                if (ret) {
-                       event = ERR_PTR(-EINVAL);
+                       ret = -EINVAL;
                        goto register_error;
                }
                break;
@@ -415,7 +415,7 @@ struct lttng_event *lttng_event_create(struct lttng_channel *chan,
                                event_param->u.kprobe.addr,
                                event);
                if (ret) {
-                       event = ERR_PTR(-EINVAL);
+                       ret = -EINVAL;
                        goto register_error;
                }
                ret = try_module_get(event->desc->owner);
@@ -429,7 +429,7 @@ struct lttng_event *lttng_event_create(struct lttng_channel *chan,
                event_return =
                        kmem_cache_zalloc(event_cache, GFP_KERNEL);
                if (!event_return) {
-                       event = ERR_PTR(-ENOMEM);
+                       ret = -ENOMEM;
                        goto register_error;
                }
                event_return->chan = chan;
@@ -448,7 +448,7 @@ struct lttng_event *lttng_event_create(struct lttng_channel *chan,
                                event, event_return);
                if (ret) {
                        kmem_cache_free(event_cache, event_return);
-                       event = ERR_PTR(-EINVAL);
+                       ret = -EINVAL;
                        goto register_error;
                }
                /* Take 2 refs on the module: one per event. */
@@ -463,7 +463,6 @@ struct lttng_event *lttng_event_create(struct lttng_channel *chan,
                        kmem_cache_free(event_cache, event_return);
                        module_put(event->desc->owner);
                        module_put(event->desc->owner);
-                       event = ERR_PTR(ret);
                        goto statedump_error;
                }
                list_add(&event_return->list, &chan->session->events);
@@ -474,7 +473,6 @@ struct lttng_event *lttng_event_create(struct lttng_channel *chan,
                                event_param->u.ftrace.symbol_name,
                                event);
                if (ret) {
-                       event = ERR_PTR(ret);
                        goto register_error;
                }
                ret = try_module_get(event->desc->owner);
@@ -483,19 +481,18 @@ struct lttng_event *lttng_event_create(struct lttng_channel *chan,
        case LTTNG_KERNEL_NOOP:
                event->desc = internal_desc;
                if (!event->desc) {
-                       event = ERR_PTR(-EINVAL);
+                       ret = -EINVAL;
                        goto register_error;
                }
                break;
        default:
                WARN_ON_ONCE(1);
-               event = ERR_PTR(-EINVAL);
+               ret = -EINVAL;
                goto register_error;
        }
        ret = _lttng_event_metadata_statedump(chan->session, chan, event);
        WARN_ON_ONCE(ret > 0);
        if (ret) {
-               event = ERR_PTR(ret);
                goto statedump_error;
        }
        list_add(&event->list, &chan->session->events);
@@ -510,7 +507,7 @@ cache_error:
 exist:
 full:
        mutex_unlock(&sessions_mutex);
-       return event;
+       return ERR_PTR(ret);
 }
 
 /*