From 7e967fd0b84a843b2475acc67a5a8df138c5f5c0 Mon Sep 17 00:00:00 2001 From: Jason Gunthorpe Date: Tue, 4 Aug 2015 17:13:32 -0600 Subject: [PATCH] IB/ucma: Fix theoretical user triggered use-after-free Something like this: CPU A CPU B Acked-by: Sean Hefty ======================== ================================ ucma_destroy_id() wait_for_completion() .. anything ucma_put_ctx() complete() .. continues ... ucma_leave_multicast() mutex_lock(mut) atomic_inc(ctx->ref) mutex_unlock(mut) ucma_free_ctx() ucma_cleanup_multicast() mutex_lock(mut) kfree(mc) rdma_leave_multicast(mc->ctx->cm_id,.. Fix it by latching the ref at 0. Once it goes to 0 mc and ctx cannot leave the mutex(mut) protection. The other atomic_inc in ucma_get_ctx is OK because mutex(mut) protects it from racing with ucma_destroy_id. Signed-off-by: Jason Gunthorpe Acked-by: Sean Hefty Signed-off-by: Doug Ledford --- drivers/infiniband/core/ucma.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c index 29b21213ea75..acac9eafdbf6 100644 --- a/drivers/infiniband/core/ucma.c +++ b/drivers/infiniband/core/ucma.c @@ -1321,10 +1321,10 @@ static ssize_t ucma_leave_multicast(struct ucma_file *file, mc = ERR_PTR(-ENOENT); else if (mc->ctx->file != file) mc = ERR_PTR(-EINVAL); - else { + else if (!atomic_inc_not_zero(&mc->ctx->ref)) + mc = ERR_PTR(-ENXIO); + else idr_remove(&multicast_idr, mc->id); - atomic_inc(&mc->ctx->ref); - } mutex_unlock(&mut); if (IS_ERR(mc)) { -- 2.20.1