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Use of NullPointerException Catch to Detect NULL Pointer Dereference Affecting kernel-debug package, versions *

Severity

 Recommended
low

Based on CentOS security rating.

Threat Intelligence

EPSS
0.04% (12th percentile)

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  • Snyk IDSNYK-CENTOS6-KERNELDEBUG-7051546
  • published23 May 2024
  • disclosed21 May 2024
Report a new vulnerability Found a mistake?

Introduced: 21 May 2024

CVE-2023-52879  (opens in a new tab)
CWE-395  (opens in a new tab)

How to fix?

There is no fixed version for Centos:6 kernel-debug.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-debug package and not the kernel-debug package as distributed by Centos. See How to fix? for Centos:6 relevant fixed versions and status.

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.

CVSS Scores

version 3.1