Headline
CVE-2022-1205: security - CVE-2022-1205 kernel: Null pointer dereference and use-after-free in net/ax25/ax25_timer.c
A NULL pointer dereference flaw was found in the Linux kernel’s Amateur Radio AX.25 protocol functionality in the way a user connects with the protocol. This flaw allows a local user to crash the system.
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Date: Sat, 2 Apr 2022 16:14:37 +0800 (GMT+08:00) From: 周多明 <duoming@…edu.cn> To: oss-security@…ts.openwall.com Subject: CVE-2022-1205 kernel: Null pointer dereference and use-after-free in net/ax25/ax25_timer.c
Hello there,
There are NPD and use-after-free vulnerabilities in net/ax25/ax25_timer.c of linux that allow attacker to crash linux kernel by simulating ax25 device from user space.
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There are race conditions that may lead to null pointer dereferences in ax25_heartbeat_expiry(), ax25_t1timer_expiry(), ax25_t2timer_expiry(), ax25_t3timer_expiry() and ax25_idletimer_expiry(), when we use ax25_kill_by_device() to detach the ax25 device.
One of the race conditions that cause null pointer dereferences can be shown as below:
(Thread 1) | (Thread 2)
ax25_connect() | ax25_std_establish_data_link() | ax25_start_t1timer() | mod_timer(&ax25->t1timer,…) | | ax25_kill_by_device() (wait a time) | … | s->ax25_dev = NULL; //(1) ax25_t1timer_expiry() | ax25->ax25_dev->values[…] //(2)| … … |
We set null to ax25_cb->ax25_dev in position (1) and dereference the null pointer in position (2).
There are also race conditions that may lead to UAF bugs in ax25_heartbeat_expiry(), ax25_t1timer_expiry(), ax25_t2timer_expiry(), ax25_t3timer_expiry() and ax25_idletimer_expiry(), when we call ax25_release() to deallocate ax25_dev.
(Thread 1) | (Thread 2)
ax25_dev_device_up() //(1) | … | ax25_kill_by_device() ax25_bind() //(2) | ax25_connect() | … ax25_std_establish_data_link() | ax25_start_t1timer() | ax25_dev_device_down() //(3) mod_timer(&ax25->t1timer,…) | | ax25_release() (wait a time) | … | ax25_dev_put(ax25_dev) //(4)FREE ax25_t1timer_expiry() | ax25->ax25_dev->values[…] //USE| … … |
We increase the refcount of ax25_dev in position (1) and (2), and decrease the refcount of ax25_dev in position (3) and (4). The ax25_dev will be freed in position (4) and be used in ax25_t1timer_expiry().
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We can successfully trigger the NPD and UAF vulnerabilities to crash the linux kernel.
BUG: kernel NULL pointer dereference, address: 0000000000000050 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.17.0-rc6-00794-g45690b7d0 RIP: 0010:ax25_t1timer_expiry+0x12/0x40 … Call Trace: call_timer_fn+0x21/0x120 __run_timers.part.0+0x1ca/0x250 run_timer_softirq+0x2c/0x60 __do_softirq+0xef/0x2f3 irq_exit_rcu+0xb6/0x100 sysvec_apic_timer_interrupt+0xa2/0xd0 …
==============================================================
[ 106.116942] BUG: KASAN: use-after-free in ax25_t1timer_expiry+0x1c/0x60 [ 106.116942] Read of size 8 at addr ffff88800bda9028 by task swapper/0/0 [ 106.116942] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.17.0-06123-g0905eec574 [ 106.116942] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-14 [ 106.116942] Call Trace: … [ 106.116942] ax25_t1timer_expiry+0x1c/0x60 [ 106.116942] call_timer_fn+0x122/0x3d0 [ 106.116942] __run_timers.part.0+0x3f6/0x520 [ 106.116942] run_timer_softirq+0x4f/0xb0 [ 106.116942] __do_softirq+0x1c2/0x651 …
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The patch that have been applied to mainline Linux kernel is shown below. https://github.com/torvalds/linux/commit/fc6d01ff9ef03b66d4a3a23b46fc3c3d8cf92009 https://github.com/torvalds/linux/commit/82e31755e55fbcea6a9dfaae5fe4860ade17cbc0
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2022-03-21: commit fc6d01ff9ef0 accepted to mainline kernel 2022-03-29: commit 82e31755e55f accepted to mainline kernel 2022-04-01: CVE-2022-1205 is assigned
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Duoming Zhou <duoming@…edu.cn>
Best Regards, Duoming Zhou
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