From: "Tze-nan Wu" Tze-nan.Wu@mediatek.com
Currently, the "last_cmd" variable can be accessed by multiple processes asynchronously when multiple users manipulate synthetic_events node at the same time, it could lead to use-after-free or double-free.
This patch add "lastcmd_mutex" to prevent "last_cmd" from being accessed asynchronously.
================================================================
It's easy to reproduce in the KASAN environment by running the two scripts below in different shells.
script 1: while : do echo -n -e '\x88' > /sys/kernel/tracing/synthetic_events done
script 2: while : do echo -n -e '\xb0' > /sys/kernel/tracing/synthetic_events done
================================================================ double-free scenario:
process A process B ------------------- --------------- 1.kstrdup last_cmd 2.free last_cmd 3.free last_cmd(double-free)
================================================================ use-after-free scenario:
process A process B ------------------- --------------- 1.kstrdup last_cmd 2.free last_cmd 3.tracing_log_err(use-after-free)
================================================================
Appendix 1. KASAN report double-free:
BUG: KASAN: double-free in kfree+0xdc/0x1d4 Free of addr ***** by task sh/4879 Call trace: ... kfree+0xdc/0x1d4 create_or_delete_synth_event+0x60/0x1e8 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ...
Allocated by task 4879: ... kstrdup+0x5c/0x98 create_or_delete_synth_event+0x6c/0x1e8 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ...
Freed by task 5464: ... kfree+0xdc/0x1d4 create_or_delete_synth_event+0x60/0x1e8 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ...
================================================================ Appendix 2. KASAN report use-after-free:
BUG: KASAN: use-after-free in strlen+0x5c/0x7c Read of size 1 at addr ***** by task sh/5483 sh: CPU: 7 PID: 5483 Comm: sh ... __asan_report_load1_noabort+0x34/0x44 strlen+0x5c/0x7c tracing_log_err+0x60/0x444 create_or_delete_synth_event+0xc4/0x204 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ...
Allocated by task 5483: ... kstrdup+0x5c/0x98 create_or_delete_synth_event+0x80/0x204 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ...
Freed by task 5480: ... kfree+0xdc/0x1d4 create_or_delete_synth_event+0x74/0x204 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ...
Fixes: 27c888da9867 ("tracing: Remove size restriction on synthetic event cmd error logging") Cc: stable@vger.kernel.org Signed-off-by: Tze-nan Wu Tze-nan.Wu@mediatek.com --- kernel/trace/trace_events_synth.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c index 46d0abb32d0f..f0ff730125bf 100644 --- a/kernel/trace/trace_events_synth.c +++ b/kernel/trace/trace_events_synth.c @@ -44,14 +44,21 @@ enum { ERRORS };
static const char *err_text[] = { ERRORS };
+DEFINE_MUTEX(lastcmd_mutex); static char *last_cmd;
static int errpos(const char *str) { + int ret = 0; + + mutex_lock(&lastcmd_mutex); if (!str || !last_cmd) - return 0; + goto out;
- return err_pos(last_cmd, str); + ret = err_pos(last_cmd, str); + out: + mutex_unlock(&lastcmd_mutex); + return ret; }
static void last_cmd_set(const char *str) @@ -59,18 +66,22 @@ static void last_cmd_set(const char *str) if (!str) return;
+ mutex_lock(&lastcmd_mutex); kfree(last_cmd); - last_cmd = kstrdup(str, GFP_KERNEL); + mutex_unlock(&lastcmd_mutex); }
static void synth_err(u8 err_type, u16 err_pos) { + mutex_lock(&lastcmd_mutex); if (!last_cmd) - return; + goto out;
tracing_log_err(NULL, "synthetic_events", last_cmd, err_text, err_type, err_pos); + out: + mutex_unlock(&lastcmd_mutex); }
static int create_synth_event(const char *raw_command);