CVE-2023-53478

In the Linux kernel, the following vulnerability has been resolved:

tracing/synthetic: Fix races on freeing last_cmd

Currently, the "lastcmd" variable can be accessed by multiple processes asynchronously when multiple users manipulate syntheticevents node at the same time, it could lead to use-after-free or double-free.

This patch add "lastcmdmutex" to prevent "lastcmd" 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 lastcmd 2.free lastcmd 3.free last_cmd(double-free)

================================================================ use-after-free scenario:

process A                       process B

------------------- --------------- 1.kstrdup lastcmd 2.free lastcmd 3.tracinglogerr(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 createordeletesynthevent+0x60/0x1e8 traceparseruncommand+0x2bc/0x4b8 syntheventswrite+0x20/0x30 vfswrite+0x200/0x830 ...

Allocated by task 4879: ... kstrdup+0x5c/0x98 createordeletesynthevent+0x6c/0x1e8 traceparseruncommand+0x2bc/0x4b8 syntheventswrite+0x20/0x30 vfswrite+0x200/0x830 ...

Freed by task 5464: ... kfree+0xdc/0x1d4 createordeletesynthevent+0x60/0x1e8 traceparseruncommand+0x2bc/0x4b8 syntheventswrite+0x20/0x30 vfswrite+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 ... _asanreportload1noabort+0x34/0x44 strlen+0x5c/0x7c tracinglogerr+0x60/0x444 createordeletesynthevent+0xc4/0x204 traceparseruncommand+0x2bc/0x4b8 syntheventswrite+0x20/0x30 vfswrite+0x200/0x830 ...

Allocated by task 5483: ... kstrdup+0x5c/0x98 createordeletesynthevent+0x80/0x204 traceparseruncommand+0x2bc/0x4b8 syntheventswrite+0x20/0x30 vfswrite+0x200/0x830 ...

Freed by task 5480: ... kfree+0xdc/0x1d4 createordeletesynthevent+0x74/0x204 traceparseruncommand+0x2bc/0x4b8 syntheventswrite+0x20/0x30 vfswrite+0x200/0x830 ...