tracing: Fix fields of struct trace_iterator that are zeroed by mistake

commit ed5467da0e369e65b247b99eb6403cb79172bcda upstream.

tracing_read_pipe zeros all fields bellow "seq". The declaration contains
a comment about that, but it doesn't help.

The first field is "snapshot", it's true when current open file is
snapshot. Looks obvious, that it should not be zeroed.

The second field is "started". It was converted from cpumask_t to
cpumask_var_t (v2.6.28-4983-g4462344), in other words it was
converted from cpumask to pointer on cpumask.

Currently the reference on "started" memory is lost after the first read
from tracing_read_pipe and a proper object will never be freed.

The "started" is never dereferenced for trace_pipe, because trace_pipe
can't have the TRACE_FILE_ANNOTATE options.

Link: http://lkml.kernel.org/r/1375463803-3085183-1-git-send-email-avagin@openvz.org

Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 7 insertions, 4 deletions

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 4372658c73ae..44cdc11b15c2 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -78,6 +78,11 @@ struct trace_iterator {
         /* trace_seq for __print_flags() and __print_symbolic() etc. */
         struct trace_seq        tmp_seq;
 
+        cpumask_var_t           started;
+
+        /* it's true when current open file is snapshot */
+        bool                    snapshot;
+
         /* The below is zeroed out in pipe_read */
         struct trace_seq        seq;
         struct trace_entry      *ent;
@@ -90,10 +95,7 @@ struct trace_iterator {
         loff_t                  pos;
         long                    idx;
 
-        cpumask_var_t           started;
-
-        /* it's true when current open file is snapshot */
-        bool                    snapshot;
+        /* All new field here will be zeroed out in pipe_read */
 };
 
 enum trace_iter_flags {
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f7bc3ce6eaf6..2a250a2aa028 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4121,6 +4121,7 @@ waitagain:
         memset(&iter->seq, 0,
                sizeof(struct trace_iterator) -
                offsetof(struct trace_iterator, seq));
+        cpumask_clear(iter->started);
         iter->pos = -1;
 
         trace_event_read_lock();