| From 70c8217acd4383e069fe1898bbad36ea4fcdbdcc Mon Sep 17 00:00:00 2001 |
| From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org> |
| Date: Fri, 17 Jun 2016 16:10:42 -0400 |
| Subject: tracing: Handle NULL formats in hold_module_trace_bprintk_format() |
| |
| From: Steven Rostedt (Red Hat) <rostedt@goodmis.org> |
| |
| commit 70c8217acd4383e069fe1898bbad36ea4fcdbdcc upstream. |
| |
| If a task uses a non constant string for the format parameter in |
| trace_printk(), then the trace_printk_fmt variable is set to NULL. This |
| variable is then saved in the __trace_printk_fmt section. |
| |
| The function hold_module_trace_bprintk_format() checks to see if duplicate |
| formats are used by modules, and reuses them if so (saves them to the list |
| if it is new). But this function calls lookup_format() that does a strcmp() |
| to the value (which is now NULL) and can cause a kernel oops. |
| |
| This wasn't an issue till 3debb0a9ddb ("tracing: Fix trace_printk() to print |
| when not using bprintk()") which added "__used" to the trace_printk_fmt |
| variable, and before that, the kernel simply optimized it out (no NULL value |
| was saved). |
| |
| The fix is simply to handle the NULL pointer in lookup_format() and have the |
| caller ignore the value if it was NULL. |
| |
| Link: http://lkml.kernel.org/r/1464769870-18344-1-git-send-email-zhengjun.xing@intel.com |
| |
| Reported-by: xingzhen <zhengjun.xing@intel.com> |
| Acked-by: Namhyung Kim <namhyung@kernel.org> |
| Fixes: 3debb0a9ddb ("tracing: Fix trace_printk() to print when not using bprintk()") |
| Signed-off-by: Steven Rostedt <rostedt@goodmis.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| kernel/trace/trace_printk.c | 7 ++++++- |
| 1 file changed, 6 insertions(+), 1 deletion(-) |
| |
| --- a/kernel/trace/trace_printk.c |
| +++ b/kernel/trace/trace_printk.c |
| @@ -36,6 +36,10 @@ struct trace_bprintk_fmt { |
| static inline struct trace_bprintk_fmt *lookup_format(const char *fmt) |
| { |
| struct trace_bprintk_fmt *pos; |
| + |
| + if (!fmt) |
| + return ERR_PTR(-EINVAL); |
| + |
| list_for_each_entry(pos, &trace_bprintk_fmt_list, list) { |
| if (!strcmp(pos->fmt, fmt)) |
| return pos; |
| @@ -57,7 +61,8 @@ void hold_module_trace_bprintk_format(co |
| for (iter = start; iter < end; iter++) { |
| struct trace_bprintk_fmt *tb_fmt = lookup_format(*iter); |
| if (tb_fmt) { |
| - *iter = tb_fmt->fmt; |
| + if (!IS_ERR(tb_fmt)) |
| + *iter = tb_fmt->fmt; |
| continue; |
| } |
| |