From: "Steven Rostedt (Red Hat)" <[email protected]>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
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/[email protected]
Reported-by: xingzhen <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Fixes: 3debb0a9ddb ("tracing: Fix trace_printk() to print when not using
bprintk()")
Signed-off-by: Steven Rostedt <[email protected]>
Signed-off-by: Jiri Slaby <[email protected]>
---
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 7b900474209d..6973eeca7d99 100644
--- 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(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;
}
--
2.9.3
