tracing: Add paranoid size check in trace_printk_seq()

To be really paranoid about writing out of bound data in
trace_printk_seq(), add another check of len compared to size.

Link: http://lkml.kernel.org/r/20141119144004.GB2332@dhcp128.suse.cz

Suggested-by: Petr Mladek <pmladek@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9023446b2c2b..26facec4625e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6656,6 +6656,14 @@ trace_printk_seq(struct trace_seq *s)
         if (s->seq.len >= TRACE_MAX_PRINT)
                 s->seq.len = TRACE_MAX_PRINT;
 
+        /*
+         * More paranoid code. Although the buffer size is set to
+         * PAGE_SIZE, and TRACE_MAX_PRINT is 1000, this is just
+         * an extra layer of protection.
+         */
+        if (WARN_ON_ONCE(s->seq.len >= s->seq.size))
+                s->seq.len = s->seq.size - 1;
+
         /* should be zero ended, but we are paranoid. */
         s->buffer[s->seq.len] = 0;