CVE-2022-49006 Information

Description

In the Linux kernel the following vulnerability has been resolved:

tracing: Free buffers when a used dynamic event is removed

After 65536 dynamic events have been added and removed the ype\ field of the event then uses the first type number that is available (not currently used by other events). A type number is the identifier of the binary blobs in the tracing ring buffer (known as events) to map them to logic that can parse the binary blob.

The issue is that if a dynamic event (like a kprobe event) is traced and is in the ring buffer and then that event is removed (because it is dynamic which means it can be created and destroyed) if another dynamic event is created that has the same number that new event’s logic on parsing the binary blob will be used.

To show how this can be an issue the following can crash the kernel:

cd /sys/kernel/tracing for i in seq 65536; do echo ‘p:kprobes/foo do_sys_openat2 $arg1:u32’ > kprobe_events done

For every iteration of the above the writing to the kprobe_events will remove the old event and create a new one (with the same format) and increase the type number to the next available on until the type number reaches over 65535 which is the max number for the 16 bit type. After it reaches that number the logic to allocate a new number simply looks for the next available number. When an dynamic event is removed that number is then available to be reused by the next dynamic event created. That is once the above reaches the max number the number assigned to the event in that loop will remain the same.

Now that means deleting one dynamic event and created another will reuse the previous events type number. This is where bad things can happen. After the above loop finishes the kprobes/foo event which reads the do_sys_openat2 function call’s first parameter as an integer.

echo 1 > kprobes/foo/enable cat /etc/passwd > /dev/null cat trace cat-2211 [005] …. 2007.849603: foo: (do_sys_openat2+0x0/0x130) arg1=4294967196 cat-2211 [005] …. 2007.849620: foo: (do_sys_openat2+0x0/0x130) arg1=4294967196 cat-2211 [005] …. 2007.849838: foo: (do_sys_openat2+0x0/0x130) arg1=4294967196 cat-2211 [005] …. 2007.849880: foo: (do_sys_openat2+0x0/0x130) arg1=4294967196 echo 0 > kprobes/foo/enable

Now if we delete the kprobe and create a new one that reads a string:

echo ‘p:kprobes/foo do_sys_openat2 +0($arg2):string’ > kprobe_events

And now we can the trace:

cat trace sendmail-1942 [002] ….. 530.136320: foo: (do_sys_openat2+0x0/0x240) arg1= cat-2046 [004] ….. 530.930817: foo: (do_sys_openat2+0x0/0x240) arg1=????????????????????????????????????????????????????????????????????????????????????????????????\n cat-2046 [004] ….. 530.930961: foo: (do_sys_openat2+0x0/0x240) arg1=????????????????????????????????????????????????????????????????????????????????????????????????\n cat-2046 [004] ….. 530.934278: foo: (do_sys_openat2+0x0/0x240) arg1=????????????????????????????????????????????????????????????????????????????????????????????????\n cat-2046 [004] ….. 530.934563: foo: (do_sys_openat2+0x0/0x240) arg1=???????????????????????????????????????

truncated—

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Reference

https://git.kernel.org/stable/c/1603feac154ff38514e8354e3079a455eb4801e2 https://git.kernel.org/stable/c/be111ebd8868d4b7c041cb3c6102e1ae27d6dc1d https://git.kernel.org/stable/c/417d5ea6e735e5d88ffb6c436cf2938f3f476dd1 https://git.kernel.org/stable/c/c52d0c8c4f38f7580cff61c4dfe1034c580cedfd https://git.kernel.org/stable/c/4313e5a613049dfc1819a6dfb5f94cf2caff9452

Attack Complexity

LOW

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

HIGH

Availability Impact

HIGH

Base Score

HIGH

Base Severity

7.8