CVE-2023-52879

In the Linux kernel, the following vulnerability has been resolved:
tracing: Have trace_event_file have ref counters The following can crash
the kernel: # cd /sys/kernel/tracing # echo ‘p:sched schedule’ >
kprobe_events # exec 5>>events/kprobes/sched/enable # > kprobe_events #
exec 5>&- The above commands: 1. Change directory to the tracefs directory
2. Create a kprobe event (doesn’t matter what one) 3. Open bash file
descriptor 5 on the enable file of the kprobe event 4. Delete the kprobe
event (removes the files too) 5. Close the bash file descriptor 5 The above
causes a crash! BUG: kernel NULL pointer dereference, address:
0000000000000028 #PF: supervisor read access in kernel mode #PF:
error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT
SMP PTI CPU: 6 PID: 877 Comm: bash Not tainted
6.5.0-rc4-test-00008-g2c6b6b1029d4-dirty #186 Hardware name: QEMU Standard
PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 RIP:
0010:tracing_release_file_tr+0xc/0x50 What happens here is that the kprobe
event creates a trace_event_file “file” descriptor that represents the file
in tracefs to the event. It maintains state of the event (is it enabled for
the given instance?). Opening the “enable” file gets a reference to the
event “file” descriptor via the open file descriptor. When the kprobe event
is deleted, the file is also deleted from the tracefs system which also
frees the event “file” descriptor. But as the tracefs file is still opened
by user space, it will not be totally removed until the final dput() is
called on it. But this is not true with the event “file” descriptor that is
already freed. If the user does a write to or simply closes the file
descriptor it will reference the event “file” descriptor that was just
freed, causing a use-after-free bug. To solve this, add a ref count to the
event “file” descriptor as well as a new flag called “FREED”. The “file”
will not be freed until the last reference is released. But the FREE flag
will be set when the event is removed to prevent any more modifications to
that event from happening, even if there’s still a reference to the event
“file” descriptor.