Description

In the Linux kernel, the following vulnerability has been resolved: RDMA/rxe: Reject non-8-byte ATOMIC_WRITE payloads atomic_write_reply() at drivers/infiniband/sw/rxe/rxe_resp.c unconditionally dereferences 8 bytes at payload_addr(pkt): value = *(u64 *)payload_addr(pkt); check_rkey() previously accepted an ATOMIC_WRITE request with pktlen == resid == 0 because the length validation only compared pktlen against resid. A remote initiator that sets the RETH length to 0 therefore reaches atomic_write_reply() with a zero-byte logical payload, and the responder reads sizeof(u64) bytes from past the logical end of the packet into skb->head tailroom, then writes those 8 bytes into the attacker's MR via rxe_mr_do_atomic_write(). That is a remote disclosure of 4 bytes of kernel tailroom per probe (the other 4 bytes are the packet's own trailing ICRC). IBA oA19-28 defines ATOMIC_WRITE as exactly 8 bytes. Anything else is protocol-invalid. Hoist a strict length check into check_rkey() so the responder never reaches the unchecked dereference, and keep the existing WRITE-family length logic for the normal RDMA WRITE path. Reproduced on mainline with an unmodified rxe driver: a sustained zero-length ATOMIC_WRITE probe repeatedly leaks adjacent skb head-buffer bytes into the attacker's MR, including recognisable kernel strings and partial kernel-direct-map pointer words. With this patch applied the responder rejects the PDU and the MR stays all-zero.

References 5

• git.kernel.org https://git.kernel.org/stable/c/105bf79a23b85cf3a761d18a4f3e10ce88526bc1
• git.kernel.org https://git.kernel.org/stable/c/1114c87aa6f195cf07da55a27b2122ae26557b26
• git.kernel.org https://git.kernel.org/stable/c/539cabb7b2d8ba70f55bba91db55faef11c2a6d7
• git.kernel.org https://git.kernel.org/stable/c/7ec1ed4747f5f99f8b797bb438c5efd36079fad5
• git.kernel.org https://git.kernel.org/stable/c/d415fce3fcde6d7aeea6c25362a395b905811452

Remediation