CVE-2022-49814

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

kcm: close race conditions on sk_receive_queue

sk->sk_receive_queue is protected by skb queue lock, but for KCM sockets its RX path takes mux->rx_lock to protect more than just skb queue. However, kcm_recvmsg() still only grabs the skb queue lock, so race conditions still exist.

We can teach kcm_recvmsg() to grab mux->rx_lock too but this would introduce a potential performance regression as struct kcm_mux can be shared by multiple KCM sockets.

So we have to enforce skb queue lock in requeue_rx_msgs() and handle skb peek case carefully in kcm_wait_data(). Fortunately, skb_recv_datagram() already handles it nicely and is widely used by other sockets, we can just switch to skb_recv_datagram() after getting rid of the unnecessary sock lock in kcm_recvmsg() and kcm_splice_read(). Side note: SOCK_DONE is not used by KCM sockets, so it is safe to get rid of this check too.

I ran the original syzbot reproducer for 30 min without seeing any issue.

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/22f6b5d47396b4287662668ee3f5c1f766cb4259
• https://git.kernel.org/stable/c/4154b6afa2bd639214ff259d912faad984f7413a
• https://git.kernel.org/stable/c/5121197ecc5db58c07da95eb1ff82b98b121a221
• https://git.kernel.org/stable/c/bf92e54597d842da127c59833b365d6faeeaf020
• https://git.kernel.org/stable/c/ce57d6474ae999a3b2d442314087473a646a65c7
• https://git.kernel.org/stable/c/d9ad4de92e184b19bcae4da10dac0275abf83931
• https://git.kernel.org/stable/c/f7b0e95071bb4be4b811af3f0bfc3e200eedeaa3