CVE-2024-40910 ax25: Fix refcount imbalance on inbound connections
A refcount imbalance in the Linux kernel AX.25 protocol allows attackers to trigger use-after-free errors and kernel crashes, causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-40910?
CVE-2024-40910 is a high-severity use after free vulnerability in Linux kernel, published on 12 Jul 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ax25: Fix refcount imbalance on inbound connections
When releasing a socket in ax25_release(), we call netdev_put() to decrease the refcount on the associated ax.25 device. However, the execution path for accepting an incoming connection never calls netdev_hold(). This imbalance leads to refcount errors, and ultimately to kernel crashes.
A typical call trace for the above situation will start with one of the following errors:
refcount_t: decrement hit 0; leaking memory. refcount_t: underflow; use-after-free.
And will then have a trace like:
Call Trace: <TASK> ? show_regs+0x64/0x70 ? __warn+0x83/0x120 ? refcount_warn_saturate+0xb2/0x100 ? report_bug+0x158/0x190 ? prb_read_valid+0x20/0x30 ? handle_bug+0x3e/0x70 ? exc_invalid_op+0x1c/0x70 ? asm_exc_invalid_op+0x1f/0x30 ? refcount_warn_saturate+0xb2/0x100 ? refcount_warn_saturate+0xb2/0x100 ax25_release+0x2ad/0x360 __sock_release+0x35/0xa0 sock_close+0x19/0x20 [...]
On reboot (or any attempt to remove the interface), the kernel gets stuck in an infinite loop:
unregister_netdevice: waiting for ax0 to become free. Usage count = 0
This patch corrects these issues by ensuring that we call netdev_hold() and ax25_dev_hold() for new connections in ax25_accept(). This makes the logic leading to ax25_accept() match the logic for ax25_bind(): in both cases we increment the refcount, which is ultimately decremented in ax25_release().
Which versions are affected by CVE-2024-40910?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-40910?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2024-40910 being exploited?
There is no known exploitation of CVE-2024-40910 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-40910, DEBIAN-CVE-2024-40910, GHSA-37qc-prgq-xwcm, ROOT-OS-DEBIAN-11-CVE-2024-40910, UBUNTU-CVE-2024-40910.