CVE-2026-74394: RDMA/srpt: fix integer overflow in immediate data length check

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

RDMA/srpt: fix integer overflow in immediate data length check

immbuf->len is a user-controlled uint32t received from the network. Adding it to immdataoffset without overflow checking allows a malicious initiator to send len=0xFFFFFFFF, causing reqsize to wrap around to a small value, bypassing the bounds check, and subsequently passing a ~4GB length to sginitone().

Use checkaddoverflow() to detect wrapping before the comparison.