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

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@kernel.org>
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@kernel.org

Fixes: 0c8916c34203 ("tracing: Add rmdir to remove multibuffer instances")
Cc: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

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 */
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