infiniband: fix a possible use-after-free bug

ucma_process_join() will free the new allocated "mc" struct,
if there is any error after that, especially the copy_to_user().

But in parallel, ucma_leave_multicast() could find this "mc"
through idr_find() before ucma_process_join() frees it, since it
is already published.

So "mc" could be used in ucma_leave_multicast() after it is been
allocated and freed in ucma_process_join(), since we don't refcnt
it.

Fix this by separating "publish" from ID allocation, so that we
can get an ID first and publish it later after copy_to_user().

Fixes: c8f6a362bf3e ("RDMA/cma: Add multicast communication support")
Reported-by: Noam Rathaus <noamr@beyondsecurity.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
index eab43b17e9cf24f6f2bd1152dbc3cb2f188757a3..ec8fb289621fb7590dd3e3f4000967fa2b6c9aae 100644 (file)
--- a/drivers/infiniband/core/ucma.c
+++ b/drivers/infiniband/core/ucma.c
@@ -235,7 +235,7 @@ static struct ucma_multicast* ucma_alloc_multicast(struct ucma_context *ctx)
                return NULL;
 
        mutex_lock(&mut);
-       mc->id = idr_alloc(&multicast_idr, mc, 0, 0, GFP_KERNEL);
+       mc->id = idr_alloc(&multicast_idr, NULL, 0, 0, GFP_KERNEL);
        mutex_unlock(&mut);
        if (mc->id < 0)
                goto error;
@@ -1421,6 +1421,10 @@ static ssize_t ucma_process_join(struct ucma_file *file,
                goto err3;
        }
 
+       mutex_lock(&mut);
+       idr_replace(&multicast_idr, mc, mc->id);
+       mutex_unlock(&mut);
+
        mutex_unlock(&file->mut);
        ucma_put_ctx(ctx);
        return 0;