CVE-2025-37920

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

xsk: Fix race condition in AF_XDP generic RX path

Move rx_lock from xsk_socket to xsk_buff_pool. Fix synchronization for shared umem mode in generic RX path where multiple sockets share single xsk_buff_pool.

RX queue is exclusive to xsk_socket, while FILL queue can be shared between multiple sockets. This could result in race condition where two CPU cores access RX path of two different sockets sharing the same umem.

Protect both queues by acquiring spinlock in shared xsk_buff_pool.

Lock contention may be minimized in the future by some per-thread FQ buffering.

Its safe and necessary to move spin_lock_bh(rx_lock) after xsk_rcv_check():

• xs->pool and spinlock_init is synchronized by xsk_bind() -> xsk_is_bound() memory barriers.
• xsk_rcv_check() may return true at the moment of xsk_release() or xsk_unbind_dev(), however this will not cause any data races or race conditions. xsk_unbind_dev() removes xdp socket from all maps and waits for completion of all outstanding rx operations. Packets in RX path will either complete safely or drop.

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/65d3c570614b892257dc58a1b202908242ecf8fd
• https://git.kernel.org/stable/c/75a240a3e8abf17b9e00b0ef0492b1bbaa932251
• https://git.kernel.org/stable/c/a1356ac7749cafc4e27aa62c0c4604b5dca4983e
• https://git.kernel.org/stable/c/b6978c565ce33658543c637060852434b4248d30