CVE-2023-53478: In the Linux kernel, the following vulnerability has been resolved:  tracing/synthetic: Fix races on freeing last_cmd  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         ...