6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Quanye Yang commit 662ade4de9ff5eceb0820a9f8e9fac70ba6a815b upstream. 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 Link: https://patch.msgid.link/20260831-rdma-ucma-mc-uaf-v1-1-b8eeb7046aff@proton.me Signed-off-by: Leon Romanovsky Signed-off-by: Greg Kroah-Hartman --- drivers/infiniband/core/ucma.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --- a/drivers/infiniband/core/ucma.c +++ b/drivers/infiniband/core/ucma.c @@ -1488,9 +1488,10 @@ static ssize_t ucma_process_join(struct mutex_lock(&ctx->mutex); ret = rdma_join_multicast(ctx->cm_id, (struct sockaddr *)&mc->addr, join_state, mc); - mutex_unlock(&ctx->mutex); - if (ret) + if (ret) { + mutex_unlock(&ctx->mutex); goto err_xa_erase; + } resp.id = mc->id; if (copy_to_user(u64_to_user_ptr(cmd->response), @@ -1498,6 +1499,7 @@ static ssize_t ucma_process_join(struct ret = -EFAULT; goto err_leave_multicast; } + mutex_unlock(&ctx->mutex); xa_store(&multicast_table, mc->id, mc, 0); @@ -1505,7 +1507,6 @@ static ssize_t ucma_process_join(struct return 0; err_leave_multicast: - mutex_lock(&ctx->mutex); rdma_leave_multicast(ctx->cm_id, (struct sockaddr *) &mc->addr); mutex_unlock(&ctx->mutex); ucma_cleanup_mc_events(mc);