I agree with you. You can also add me to the "Signed-off-by". Best Regards, Zhengjun -----Original Message----- From: Steven Rostedt [mailto:rostedt@xxxxxxxxxxx] Sent: Monday, June 20, 2016 9:53 PM To: linux-kernel@xxxxxxxxxxxxxxx Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>; Ingo Molnar <mingo@xxxxxxxxxx>; Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>; Xing, Zhengjun <zhengjun.xing@xxxxxxxxx>; Namhyung Kim <namhyung@xxxxxxxxxx>; stable@xxxxxxxxxxxxxxx Subject: [PATCH 1/2] tracing: Handle NULL formats in hold_module_trace_bprintk_format() From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx> 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()") Cc: stable@xxxxxxxxxxxxxxx # v3.5+ Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> --- kernel/trace/trace_printk.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c index f96f0383f6c6..ad1d6164e946 100644 --- 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(const char **start, const char **end) 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; } -- 2.8.0.rc3 -- 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