CVE-2026-98253RDMA/ucma: Serialize join and leave on copy_to_user failure

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/29b9ed83d8bfab5c6e11fcbf1aa836aa4ae26cb9
• https://git.kernel.org/stable/c/52172e11bd074ccaded21740ffeb67123f01dd00
• https://git.kernel.org/stable/c/01e29d0d78a8f66f221625720a04939eef5ec1f6
• https://git.kernel.org/stable/c/ae805d204cf1f15b87d1bf3529b4c649f3519420
• https://git.kernel.org/stable/c/43c4e24bd10370fc976f6220518049ce71419399
• https://git.kernel.org/stable/c/01cbdb724c584d7772fd25af2e4dfdf8527ce0d5
• https://git.kernel.org/stable/c/83610ee5e498fa5bfcb80031d2b959baea276bf6
• https://git.kernel.org/stable/c/662ade4de9ff5eceb0820a9f8e9fac70ba6a815b