linux/kernel/trace/trace_printk.c
Steven Rostedt (Red Hat) 70c8217acd 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 3debb0a9dd ("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: 3debb0a9dd ("tracing: Fix trace_printk() to print when not using bprintk()")
Cc: stable@vger.kernel.org # v3.5+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2016-06-20 09:46:12 -04:00

382 lines
8.5 KiB
C

/*
* trace binary printk
*
* Copyright (C) 2008 Lai Jiangshan <laijs@cn.fujitsu.com>
*
*/
#include <linux/seq_file.h>
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/ftrace.h>
#include <linux/string.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/ctype.h>
#include <linux/list.h>
#include <linux/slab.h>
#include "trace.h"
#ifdef CONFIG_MODULES
/*
* modules trace_printk()'s formats are autosaved in struct trace_bprintk_fmt
* which are queued on trace_bprintk_fmt_list.
*/
static LIST_HEAD(trace_bprintk_fmt_list);
/* serialize accesses to trace_bprintk_fmt_list */
static DEFINE_MUTEX(btrace_mutex);
struct trace_bprintk_fmt {
struct list_head list;
const char *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;
}
return NULL;
}
static
void hold_module_trace_bprintk_format(const char **start, const char **end)
{
const char **iter;
char *fmt;
/* allocate the trace_printk per cpu buffers */
if (start != end)
trace_printk_init_buffers();
mutex_lock(&btrace_mutex);
for (iter = start; iter < end; iter++) {
struct trace_bprintk_fmt *tb_fmt = lookup_format(*iter);
if (tb_fmt) {
if (!IS_ERR(tb_fmt))
*iter = tb_fmt->fmt;
continue;
}
fmt = NULL;
tb_fmt = kmalloc(sizeof(*tb_fmt), GFP_KERNEL);
if (tb_fmt) {
fmt = kmalloc(strlen(*iter) + 1, GFP_KERNEL);
if (fmt) {
list_add_tail(&tb_fmt->list, &trace_bprintk_fmt_list);
strcpy(fmt, *iter);
tb_fmt->fmt = fmt;
} else
kfree(tb_fmt);
}
*iter = fmt;
}
mutex_unlock(&btrace_mutex);
}
static int module_trace_bprintk_format_notify(struct notifier_block *self,
unsigned long val, void *data)
{
struct module *mod = data;
if (mod->num_trace_bprintk_fmt) {
const char **start = mod->trace_bprintk_fmt_start;
const char **end = start + mod->num_trace_bprintk_fmt;
if (val == MODULE_STATE_COMING)
hold_module_trace_bprintk_format(start, end);
}
return 0;
}
/*
* The debugfs/tracing/printk_formats file maps the addresses with
* the ASCII formats that are used in the bprintk events in the
* buffer. For userspace tools to be able to decode the events from
* the buffer, they need to be able to map the address with the format.
*
* The addresses of the bprintk formats are in their own section
* __trace_printk_fmt. But for modules we copy them into a link list.
* The code to print the formats and their addresses passes around the
* address of the fmt string. If the fmt address passed into the seq
* functions is within the kernel core __trace_printk_fmt section, then
* it simply uses the next pointer in the list.
*
* When the fmt pointer is outside the kernel core __trace_printk_fmt
* section, then we need to read the link list pointers. The trick is
* we pass the address of the string to the seq function just like
* we do for the kernel core formats. To get back the structure that
* holds the format, we simply use containerof() and then go to the
* next format in the list.
*/
static const char **
find_next_mod_format(int start_index, void *v, const char **fmt, loff_t *pos)
{
struct trace_bprintk_fmt *mod_fmt;
if (list_empty(&trace_bprintk_fmt_list))
return NULL;
/*
* v will point to the address of the fmt record from t_next
* v will be NULL from t_start.
* If this is the first pointer or called from start
* then we need to walk the list.
*/
if (!v || start_index == *pos) {
struct trace_bprintk_fmt *p;
/* search the module list */
list_for_each_entry(p, &trace_bprintk_fmt_list, list) {
if (start_index == *pos)
return &p->fmt;
start_index++;
}
/* pos > index */
return NULL;
}
/*
* v points to the address of the fmt field in the mod list
* structure that holds the module print format.
*/
mod_fmt = container_of(v, typeof(*mod_fmt), fmt);
if (mod_fmt->list.next == &trace_bprintk_fmt_list)
return NULL;
mod_fmt = container_of(mod_fmt->list.next, typeof(*mod_fmt), list);
return &mod_fmt->fmt;
}
static void format_mod_start(void)
{
mutex_lock(&btrace_mutex);
}
static void format_mod_stop(void)
{
mutex_unlock(&btrace_mutex);
}
#else /* !CONFIG_MODULES */
__init static int
module_trace_bprintk_format_notify(struct notifier_block *self,
unsigned long val, void *data)
{
return 0;
}
static inline const char **
find_next_mod_format(int start_index, void *v, const char **fmt, loff_t *pos)
{
return NULL;
}
static inline void format_mod_start(void) { }
static inline void format_mod_stop(void) { }
#endif /* CONFIG_MODULES */
static bool __read_mostly trace_printk_enabled = true;
void trace_printk_control(bool enabled)
{
trace_printk_enabled = enabled;
}
__initdata_or_module static
struct notifier_block module_trace_bprintk_format_nb = {
.notifier_call = module_trace_bprintk_format_notify,
};
int __trace_bprintk(unsigned long ip, const char *fmt, ...)
{
int ret;
va_list ap;
if (unlikely(!fmt))
return 0;
if (!trace_printk_enabled)
return 0;
va_start(ap, fmt);
ret = trace_vbprintk(ip, fmt, ap);
va_end(ap);
return ret;
}
EXPORT_SYMBOL_GPL(__trace_bprintk);
int __ftrace_vbprintk(unsigned long ip, const char *fmt, va_list ap)
{
if (unlikely(!fmt))
return 0;
if (!trace_printk_enabled)
return 0;
return trace_vbprintk(ip, fmt, ap);
}
EXPORT_SYMBOL_GPL(__ftrace_vbprintk);
int __trace_printk(unsigned long ip, const char *fmt, ...)
{
int ret;
va_list ap;
if (!trace_printk_enabled)
return 0;
va_start(ap, fmt);
ret = trace_vprintk(ip, fmt, ap);
va_end(ap);
return ret;
}
EXPORT_SYMBOL_GPL(__trace_printk);
int __ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap)
{
if (!trace_printk_enabled)
return 0;
return trace_vprintk(ip, fmt, ap);
}
EXPORT_SYMBOL_GPL(__ftrace_vprintk);
static const char **find_next(void *v, loff_t *pos)
{
const char **fmt = v;
int start_index;
int last_index;
start_index = __stop___trace_bprintk_fmt - __start___trace_bprintk_fmt;
if (*pos < start_index)
return __start___trace_bprintk_fmt + *pos;
/*
* The __tracepoint_str section is treated the same as the
* __trace_printk_fmt section. The difference is that the
* __trace_printk_fmt section should only be used by trace_printk()
* in a debugging environment, as if anything exists in that section
* the trace_prink() helper buffers are allocated, which would just
* waste space in a production environment.
*
* The __tracepoint_str sections on the other hand are used by
* tracepoints which need to map pointers to their strings to
* the ASCII text for userspace.
*/
last_index = start_index;
start_index = __stop___tracepoint_str - __start___tracepoint_str;
if (*pos < last_index + start_index)
return __start___tracepoint_str + (*pos - last_index);
start_index += last_index;
return find_next_mod_format(start_index, v, fmt, pos);
}
static void *
t_start(struct seq_file *m, loff_t *pos)
{
format_mod_start();
return find_next(NULL, pos);
}
static void *t_next(struct seq_file *m, void * v, loff_t *pos)
{
(*pos)++;
return find_next(v, pos);
}
static int t_show(struct seq_file *m, void *v)
{
const char **fmt = v;
const char *str = *fmt;
int i;
if (!*fmt)
return 0;
seq_printf(m, "0x%lx : \"", *(unsigned long *)fmt);
/*
* Tabs and new lines need to be converted.
*/
for (i = 0; str[i]; i++) {
switch (str[i]) {
case '\n':
seq_puts(m, "\\n");
break;
case '\t':
seq_puts(m, "\\t");
break;
case '\\':
seq_putc(m, '\\');
break;
case '"':
seq_puts(m, "\\\"");
break;
default:
seq_putc(m, str[i]);
}
}
seq_puts(m, "\"\n");
return 0;
}
static void t_stop(struct seq_file *m, void *p)
{
format_mod_stop();
}
static const struct seq_operations show_format_seq_ops = {
.start = t_start,
.next = t_next,
.show = t_show,
.stop = t_stop,
};
static int
ftrace_formats_open(struct inode *inode, struct file *file)
{
return seq_open(file, &show_format_seq_ops);
}
static const struct file_operations ftrace_formats_fops = {
.open = ftrace_formats_open,
.read = seq_read,
.llseek = seq_lseek,
.release = seq_release,
};
static __init int init_trace_printk_function_export(void)
{
struct dentry *d_tracer;
d_tracer = tracing_init_dentry();
if (IS_ERR(d_tracer))
return 0;
trace_create_file("printk_formats", 0444, d_tracer,
NULL, &ftrace_formats_fops);
return 0;
}
fs_initcall(init_trace_printk_function_export);
static __init int init_trace_printk(void)
{
return register_module_notifier(&module_trace_bprintk_format_nb);
}
early_initcall(init_trace_printk);