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

...