CVE-2024-35982 batman-adv: Avoid infinite loop trying to resize local TT
An attacker can cause a denial of service in the Linux kernel by triggering an infinite loop in the batman-adv module when MTU constraints prevent translation table resizing.
- 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-2024-35982?
CVE-2024-35982 is a medium-severity denial of service vulnerability in Linux kernel, published on 20 May 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:
batman-adv: Avoid infinite loop trying to resize local TT
If the MTU of one of an attached interface becomes too small to transmit the local translation table then it must be resized to fit inside all fragments (when enabled) or a single packet.
But if the MTU becomes too low to transmit even the header + the VLAN specific part then the resizing of the local TT will never succeed. This can for example happen when the usable space is 110 bytes and 11 VLANs are on top of batman-adv. In this case, at least 116 byte would be needed. There will just be an endless spam of
batman_adv: batadv0: Forced to purge local tt entries to fit new maximum fragment MTU (110)
in the log but the function will never finish. Problem here is that the timeout will be halved all the time and will then stagnate at 0 and therefore never be able to reduce the table even more.
There are other scenarios possible with a similar result. The number of BATADV_TT_CLIENT_NOPURGE entries in the local TT can for example be too high to fit inside a packet. Such a scenario can therefore happen also with only a single VLAN + 7 non-purgable addresses - requiring at least 120 bytes.
While this should be handled proactively when:
* interface with too low MTU is added * VLAN is added * non-purgeable local mac is added * MTU of an attached interface is reduced * fragmentation setting gets disabled (which most likely requires dropping attached interfaces)
not all of these scenarios can be prevented because batman-adv is only consuming events without the the possibility to prevent these actions (non-purgable MAC address added, MTU of an attached interface is reduced). It is therefore necessary to also make sure that the code is able to handle also the situations when there were already incompatible system configuration are present.
Weakness: CWE-835
Which versions are affected by CVE-2024-35982?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-35982?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2024-35982 being exploited?
There is no known exploitation of CVE-2024-35982 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-42223, BELL-CVE-2024-35982, DEBIAN-CVE-2024-35982, GHSA-pmcq-c5h6-mv64, UBUNTU-CVE-2024-35982.