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.
================================================================
Its 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 …