When function tracer has a pid filter, it adds a probe to sched_switch
to track if current task can be ignored. The probe checks the
ftrace_ignore_pid from current tr to filter tasks. But it misses to
delete the probe when removing an instance so that it can cause a crash
due to the invalid tr pointer (use-after-free).
This is easily reproducible with the following:
# cd /sys/kernel/debug/tracing
# mkdir instances/buggy
# echo $$ > instances/buggy/set_ftrace_pid
# rmdir instances/buggy
============================================================================
BUG: KASAN: use-after-free in ftrace_filter_pid_sched_switch_probe+0x3d/0x90
Read of size 8 by task kworker/0:1/17
CPU: 0 PID: 17 Comm: kworker/0:1 Tainted: G B 4.11.0-rc3 #198
Call Trace:
dump_stack+0x68/0x9f
kasan_object_err+0x21/0x70
kasan_report.part.1+0x22b/0x500
? ftrace_filter_pid_sched_switch_probe+0x3d/0x90
kasan_report+0x25/0x30
__asan_load8+0x5e/0x70
ftrace_filter_pid_sched_switch_probe+0x3d/0x90
? fpid_start+0x130/0x130
__schedule+0x571/0xce0
...
To fix it, use ftrace_pid_reset() to unregister the probe. As
instance_rmdir() already updated ftrace codes, it can just free the
filter safely.
Fixes: 0c8916c34203 ("tracing: Add rmdir to remove multibuffer instances")
Signed-off-by: Namhyung Kim <[email protected]>
---
kernel/trace/ftrace.c | 10 ++++++----
kernel/trace/trace.c | 1 +
kernel/trace/trace.h | 2 ++
3 files changed, 9 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 0556a202c055..b451a860e885 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5598,13 +5598,15 @@ static void clear_ftrace_pids(struct trace_array *tr)
trace_free_pid_list(pid_list);
}
-static void ftrace_pid_reset(struct trace_array *tr)
+void ftrace_pid_reset(struct trace_array *tr, bool update)
{
mutex_lock(&ftrace_lock);
clear_ftrace_pids(tr);
- ftrace_update_pid_func();
- ftrace_startup_all(0);
+ if (update) {
+ ftrace_update_pid_func();
+ ftrace_startup_all(0);
+ }
mutex_unlock(&ftrace_lock);
}
@@ -5676,7 +5678,7 @@ ftrace_pid_open(struct inode *inode, struct file *file)
if ((file->f_mode & FMODE_WRITE) &&
(file->f_flags & O_TRUNC))
- ftrace_pid_reset(tr);
+ ftrace_pid_reset(tr, true);
ret = seq_open(file, &ftrace_pid_sops);
if (ret < 0) {
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b5d4b80f2d45..b92489dfa829 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7485,6 +7485,7 @@ static int instance_rmdir(const char *name)
tracing_set_nop(tr);
event_trace_del_tracer(tr);
+ ftrace_pid_reset(tr, false);
ftrace_destroy_function_files(tr);
tracefs_remove_recursive(tr->dir);
free_trace_buffers(tr);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 571acee52a32..4d9804fd9a2d 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -897,6 +897,7 @@ void ftrace_init_tracefs(struct trace_array *tr, struct
dentry *d_tracer);
void ftrace_init_tracefs_toplevel(struct trace_array *tr,
struct dentry *d_tracer);
int init_function_trace(void);
+void ftrace_pid_reset(struct trace_array *tr, bool update);
#else
static inline int ftrace_trace_task(struct trace_array *tr)
{
@@ -916,6 +917,7 @@ static inline void ftrace_reset_array_ops(struct
trace_array *tr) { }
static inline void ftrace_init_tracefs(struct trace_array *tr, struct dentry
*d) { }
static inline void ftrace_init_tracefs_toplevel(struct trace_array *tr, struct
dentry *d) { }
static inline int init_function_trace(void) { return 0; }
+static inline void ftrace_pid_reset(struct trace_array *tr, bool update) { }
/* ftace_func_t type is not defined, use macro instead of static inline */
#define ftrace_init_array_ops(tr, func) do { } while (0)
#endif /* CONFIG_FUNCTION_TRACER */
--
2.12.0
