CVE-2024-39296

In the Linux kernel, the following vulnerability has been resolved:

bonding: fix oops during rmmod

rmmod bonding causes an oops ever since commit cc317ea3d927 (bonding: remove redundant NULL check in debugfs function). Here are the relevant functions being called:

bonding_exit() bond_destroy_debugfs() debugfs_remove_recursive(bonding_debug_root); bonding_debug_root = NULL; <——— SET TO NULL HERE bond_netlink_fini() rtnl_link_unregister() __rtnl_link_unregister() unregister_netdevice_many_notify() bond_uninit() bond_debug_unregister() (commit removed check for bonding_debug_root == NULL) debugfs_remove() simple_recursive_removal() down_write() -> OOPS

However, reverting the bad commit does not solve the problem completely because the original code contains a race that could cause the same oops, although it was much less likely to be triggered unintentionally:

CPU1 rmmod bonding bonding_exit() bond_destroy_debugfs() debugfs_remove_recursive(bonding_debug_root);

CPU2 echo -bond0 > /sys/class/net/bonding_masters bond_uninit() bond_debug_unregister() if (!bonding_debug_root)

CPU1 bonding_debug_root = NULL;

So do NOT revert the bad commit (since the removed checks were racy anyway), and instead change the order of actions taken during module removal. The same oops can also happen if there is an error during module init, so apply the same fix there.

Weakness

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/a45835a0bb6ef7d5ddbc0714dd760de979cb6ece
• https://git.kernel.org/stable/c/cf48aee81103ca06d09d73d33fb72f1191069aa6
• https://git.kernel.org/stable/c/f07224c16678a8af54ddc059b3d2d51885d7f35e
• https://git.kernel.org/stable/c/a45835a0bb6ef7d5ddbc0714dd760de979cb6ece
• https://git.kernel.org/stable/c/cf48aee81103ca06d09d73d33fb72f1191069aa6
• https://git.kernel.org/stable/c/f07224c16678a8af54ddc059b3d2d51885d7f35e