CVE-2026-98253

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

RDMA/ucma: Serialize join and leave on copy_to_user failure

rdma_join_multicast() queues RoCE work that later reads the ucma_multicast

through event->param.ud.private_data, then list_add()s the CMA multicast

at the head of id_priv->mc_list. rdma_leave_multicast() matches only by

sockaddr and destroys the first hit.

ucma_process_join() used to drop ctx->mutex after a successful join and

retake it only if copy_to_user() failed. Two concurrent JOIN_MCAST calls

with the same address can therefore insert a second CMA entry before the

first thread's leave. leave then cancels the newer work and the older

worker still dereferences the ucma_multicast that the first thread frees.

Keep ctx->mutex held from rdma_join_multicast() through copy_to_user() and,

on -EFAULT, through rdma_leave_multicast() so leave cannot miss this join.

Do not leave if join itself failed: that path never published this address

on mc_list, and a leave-by-addr would destroy an earlier successful join.