path: root/kernel
diff options
authorSteven Rostedt (Red Hat) <>2016-06-17 16:10:42 -0400
committerSteven Rostedt <>2016-06-20 09:46:12 -0400
commit70c8217acd4383e069fe1898bbad36ea4fcdbdcc (patch)
tree4bf9451f8719b199f7a94d3cc7fa3b05409647ea /kernel
parent5edb56491d4812c42175980759da53388e5d86f5 (diff)
tracing: Handle NULL formats in hold_module_trace_bprintk_format()
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: Reported-by: xingzhen <> Acked-by: Namhyung Kim <> Fixes: 3debb0a9ddb ("tracing: Fix trace_printk() to print when not using bprintk()") Cc: # v3.5+ Signed-off-by: Steven Rostedt <>
Diffstat (limited to 'kernel')
1 files changed, 6 insertions, 1 deletions
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;