tracing: fix memory leak in trace_stat

If the function profiler does not have any items recorded and one were
to cat the function stat file, the kernel would take a BUG with a NULL
pointer dereference.

Looking further into this, I found that returning NULL from stat_start
did not stop the stat logic, and would later call stat_next. This breaks
from the way seq_file works, so I looked into fixing the stat code.

This is where I noticed that the last next_entry is never freed.
It is allocated, and if the stat_next returns NULL, the code breaks out
of the loop, unlocks the mutex and exits. We never link the next_entry
nor do we free it. Thus it is a real memory leak.

This patch rearranges the code a bit to not only fix the memory leak,
but also to act more like seq_file where nothing is printed if there
is nothing to print. That is, stat_start returns NULL.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

1 files changed, 13 insertions, 10 deletions

diff --git a/kernel/trace/trace_stat.c b/kernel/trace/trace_stat.c
index 39310e3434ee..f71b85b22cfe 100644
--- a/kernel/trace/trace_stat.c
+++ b/kernel/trace/trace_stat.c
@@ -75,7 +75,7 @@ static int stat_seq_init(struct tracer_stat_session *session)
 {
         struct trace_stat_list *iter_entry, *new_entry;
         struct tracer_stat *ts = session->ts;
-        void *prev_stat;
+        void *stat;
         int ret = 0;
         int i;
 
@@ -85,6 +85,10 @@ static int stat_seq_init(struct tracer_stat_session *session)
         if (!ts->stat_cmp)
                 ts->stat_cmp = dummy_cmp;
 
+        stat = ts->stat_start();
+        if (!stat)
+                goto exit;
+
         /*
          * The first entry. Actually this is the second, but the first
          * one (the stat_list head) is pointless.
@@ -99,14 +103,19 @@ static int stat_seq_init(struct tracer_stat_session *session)
 
         list_add(&new_entry->list, &session->stat_list);
 
-        new_entry->stat = ts->stat_start();
-        prev_stat = new_entry->stat;
+        new_entry->stat = stat;
 
         /*
          * Iterate over the tracer stat entries and store them in a sorted
          * list.
          */
         for (i = 1; ; i++) {
+                stat = ts->stat_next(stat, i);
+
+                /* End of insertion */
+                if (!stat)
+                        break;
+
                 new_entry = kmalloc(sizeof(struct trace_stat_list), GFP_KERNEL);
                 if (!new_entry) {
                         ret = -ENOMEM;
@@ -114,11 +123,7 @@ static int stat_seq_init(struct tracer_stat_session *session)
                 }
 
                 INIT_LIST_HEAD(&new_entry->list);
-                new_entry->stat = ts->stat_next(prev_stat, i);
-
-                /* End of insertion */
-                if (!new_entry->stat)
-                        break;
+                new_entry->stat = stat;
 
                 list_for_each_entry(iter_entry, &session->stat_list, list) {
 
@@ -137,8 +142,6 @@ static int stat_seq_init(struct tracer_stat_session *session)
                                 break;
                         }
                 }
-
-                prev_stat = new_entry->stat;
         }
 exit:
         mutex_unlock(&session->stat_mutex);