Subject: CVE-2023-52879: tracing: Have trace_event_file have ref counters

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2023-52879 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.4.258 with commit e6807c873d87 and fixed in 5.4.262 with commit 961c4511c757
	Issue introduced in 5.10.198 with commit 407bf1c140f0 and fixed in 5.10.202 with commit a98172e36e5f
	Issue introduced in 5.15.134 with commit fa6d449e4d02 and fixed in 5.15.140 with commit cbc7c29dff0f
	Issue introduced in 6.1.55 with commit a46bf337a20f and fixed in 6.1.64 with commit 2fa74d29fc18
	Issue introduced in 6.5.5 with commit 9beec0437013 and fixed in 6.5.13 with commit 2c9de867ca28
	Issue introduced in 6.6 with commit f5ca233e2e66 and fixed in 6.6.1 with commit 9034c87d61be
	Issue introduced in 6.6 with commit f5ca233e2e66 and fixed in 6.7 with commit bb32500fb9b7

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2023-52879
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	include/linux/trace_events.h
	kernel/trace/trace.c
	kernel/trace/trace.h
	kernel/trace/trace_events.c
	kernel/trace/trace_events_filter.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/961c4511c7578d6b8f39118be919016ec3db1c1e
	https://git.kernel.org/stable/c/a98172e36e5f1b3d29ad71fade2d611cfcc2fe6f
	https://git.kernel.org/stable/c/cbc7c29dff0fa18162f2a3889d82eeefd67305e0
	https://git.kernel.org/stable/c/2fa74d29fc1899c237d51bf9a6e132ea5c488976
	https://git.kernel.org/stable/c/2c9de867ca285c397cd71af703763fe416265706
	https://git.kernel.org/stable/c/9034c87d61be8cff989017740a91701ac8195a1d
	https://git.kernel.org/stable/c/bb32500fb9b78215e4ef6ee8b4345c5f5d7eafb4