TLDRVuln - Cybersecurity Vulnerabilities Made Simple

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

tracing/osnoise: Do not unregister events twice

Nicolas reported that using:

# trace-cmd record -e all -M 10 -p osnoise --poll

Resulted in the following kernel warning:

------------[ cut here ]------------

WARNING: CPU: 0 PID: 1217 at kernel/tracepoint.c:404 tracepoint_probe_unregister+0x280/0x370

[...]

CPU: 0 PID: 1217 Comm: trace-cmd Not tainted 5.17.0-rc6-next-20220307-nico+ #19

RIP: 0010:tracepoint_probe_unregister+0x280/0x370

[...]

CR2: 00007ff919b29497 CR3: 0000000109da4005 CR4: 0000000000170ef0

Call Trace:

<TASK>

osnoise_workload_stop+0x36/0x90

tracing_set_tracer+0x108/0x260

tracing_set_trace_write+0x94/0xd0

? __check_object_size.part.0+0x10a/0x150

? selinux_file_permission+0x104/0x150

vfs_write+0xb5/0x290

ksys_write+0x5f/0xe0

do_syscall_64+0x3b/0x90

entry_SYSCALL_64_after_hwframe+0x44/0xae

RIP: 0033:0x7ff919a18127

[...]

---[ end trace 0000000000000000 ]---

The warning complains about an attempt to unregister an

unregistered tracepoint.

This happens on trace-cmd because it first stops tracing, and

then switches the tracer to nop. Which is equivalent to:

# cd /sys/kernel/tracing/

# echo osnoise > current_tracer

# echo 0 > tracing_on

# echo nop > current_tracer

The osnoise tracer stops the workload when no trace instance

is actually collecting data. This can be caused both by

disabling tracing or disabling the tracer itself.

To avoid unregistering events twice, use the existing

trace_osnoise_callback_enabled variable to check if the events

(and the workload) are actually active before trying to

deactivate them.