3.16.37-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx> 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@xxxxxxxxx Reported-by: xingzhen <zhengjun.xing@xxxxxxxxx> Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx> Fixes: 3debb0a9ddb ("tracing: Fix trace_printk() to print when not using bprintk()") Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- 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 @@ -38,6 +38,10 @@ 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; @@ -59,7 +63,8 @@ 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; } -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html