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.

Reported-by: syzbot+a6ffe86390c8a6afc818@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a6ffe86390c8a6afc818
Fixes: fe454dc31e84 ("RDMA/ucma: Fix use-after-free bug in ucma_create_uevent")
Cc: stable@vger.kernel.org
Signed-off-by: Quanye Yang <quanyeyang@proton.me>
Link: https://patch.msgid.link/20260831-rdma-ucma-mc-uaf-v1-1-b8eeb7046aff@proton.me
Signed-off-by: Leon Romanovsky <leon@kernel.org>

0 files changed, 0 insertions, 0 deletions