CVE-2023-52879 Information

May 23, 2024 cve

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 ile\ 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 nable\ file gets a reference to the event ile\ 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 ile\ndescriptor.

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 ile\ descriptor that is already freed. If the user does a write to or simply closes the file descriptor it will reference the event ile\ descriptor that was just freed causing a use-after-free bug.

To solve this add a ref count to the event ile\ descriptor as well as a new flag called \FREED. The ile\ 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 ile\ descriptor.

Reference

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

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