[GIT PULL] ftrace: Fix function pid filter on instances

[Steven Rostedt]

Linus,

Namhyung Kim discovered a use after free bug. It has to do with adding
a pid filter to function tracing in an instance, and then freeing
the instance.


Please pull the latest trace-v4.11-rc5-3 tree, which can be found at:


  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v4.11-rc5-3

Tag SHA1: 0d943074a6344fc4beb35bc995c83d27f43c25e2
Head SHA1: d879d0b8c183aabeb9a65eba91f3f9e3c7e7b905


Namhyung Kim (1):
      ftrace: Fix function pid filter on instances

----
 kernel/trace/ftrace.c | 9 +++++++++
 kernel/trace/trace.c  | 1 +
 kernel/trace/trace.h  | 2 ++
 3 files changed, 12 insertions(+)
---------------------------
commit d879d0b8c183aabeb9a65eba91f3f9e3c7e7b905
Author: Namhyung Kim <namhyung@xxxxxxxxxx>
Date:   Mon Apr 17 11:44:27 2017 +0900

    ftrace: Fix function pid filter on instances
    
    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_clear_pids() to unregister the probe.  As
    instance_rmdir() already updated ftrace codes, it can just free the
    filter safely.
    
    Link: http://lkml.kernel.org/r/20170417024430.21194-2-namhyung@xxxxxxxxxx
    
    Fixes: 0c8916c34203 ("tracing: Add rmdir to remove multibuffer instances")
    Cc: Ingo Molnar <mingo@xxxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx
    Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
    Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 27bb2e61276e..dd3e91d68dc7 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5566,6 +5566,15 @@ static void clear_ftrace_pids(struct trace_array *tr)
 	trace_free_pid_list(pid_list);
 }
 
+void ftrace_clear_pids(struct trace_array *tr)
+{
+	mutex_lock(&ftrace_lock);
+
+	clear_ftrace_pids(tr);
+
+	mutex_unlock(&ftrace_lock);
+}
+
 static void ftrace_pid_reset(struct trace_array *tr)
 {
 	mutex_lock(&ftrace_lock);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f35109514a01..d484452ae648 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7402,6 +7402,7 @@ static int instance_rmdir(const char *name)
 
 	tracing_set_nop(tr);
 	event_trace_del_tracer(tr);
+	ftrace_clear_pids(tr);
 	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 ae1cce91fead..d19d52d600d6 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -896,6 +896,7 @@ int using_ftrace_ops_list_func(void);
 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);
+void ftrace_clear_pids(struct trace_array *tr);
 #else
 static inline int ftrace_trace_task(struct trace_array *tr)
 {
@@ -914,6 +915,7 @@ ftrace_init_global_array_ops(struct trace_array *tr) { }
 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 void ftrace_clear_pids(struct trace_array *tr) { }
 /* 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 */