CVE-2022-48848

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 tracepointprobeunregister+0x280/0x370 [...] CPU: 0 PID: 1217 Comm: trace-cmd Not tainted 5.17.0-rc6-next-20220307-nico+ #19 RIP: 0010:tracepointprobeunregister+0x280/0x370 [...] CR2: 00007ff919b29497 CR3: 0000000109da4005 CR4: 0000000000170ef0 Call Trace: <TASK> osnoiseworkloadstop+0x36/0x90 tracingsettracer+0x108/0x260 tracingsettracewrite+0x94/0xd0 ? _checkobjectsize.part.0+0x10a/0x150 ? selinuxfilepermission+0x104/0x150 vfswrite+0xb5/0x290 ksyswrite+0x5f/0xe0 dosyscall64+0x3b/0x90 entrySYSCALL64afterhwframe+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 > currenttracer # echo 0 > tracingon # 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 traceosnoisecallback_enabled variable to check if the events (and the workload) are actually active before trying to deactivate them.