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| author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2016-06-17 16:10:42 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-07-27 09:55:50 -0700 |
| commit | ef691797ae109d1305e5c6bc5da41609f7dfc35f (patch) | |
| tree | 88659bea9ba0d8f2e48ba47ca8a48f30e35afd5f /kernel | |
| parent | 22e658d19a1a64512d49de2632ad2124e6f9e429 (diff) | |
| download | lwn-ef691797ae109d1305e5c6bc5da41609f7dfc35f.tar.gz lwn-ef691797ae109d1305e5c6bc5da41609f7dfc35f.zip | |
tracing: Handle NULL formats in hold_module_trace_bprintk_format()
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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/trace/trace_printk.c | 7 |
1 files changed, 6 insertions, 1 deletions
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; } |