tracing: t_start: reset FTRACE_ITER_HASH in case of seek/pread

commit df09162550fbb53354f0c88e85b5d0e6129ee9cc upstream.

Be sure to avoid entering t_show() with FTRACE_ITER_HASH set without
having properly started the iterator to iterate the hash.  This case is
degenerate and, as discovered by Robert Swiecki, can cause t_hash_show()
to misuse a pointer.  This causes a NULL ptr deref with possible security
implications.  Tracked as CVE-2010-3079.

Cc: Robert Swiecki <swiecki@google.com>
Cc: Eugene Teo <eugene@redhat.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 67b9a3a43a20f20e426a40453480d7e7061861b4..6b316b3928a3168b41faa4b02615d05e08f56323 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1510,6 +1510,8 @@ static void *t_start(struct seq_file *m, loff_t *pos)
                if (*pos > 0)
                        return t_hash_start(m, pos);
                iter->flags |= FTRACE_ITER_PRINTALL;
+               /* reset in case of seek/pread */
+               iter->flags &= ~FTRACE_ITER_HASH;
                return iter;
        }