[PATCH 5.10 144/145] xsk: Fix memory leak for failed bind

[Greg Kroah-Hartman]

From: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>

commit 8bee683384087a6275c9183a483435225f7bb209 upstream.

Fix a possible memory leak when a bind of an AF_XDP socket fails. When
the fill and completion rings are created, they are tied to the
socket. But when the buffer pool is later created at bind time, the
ownership of these two rings are transferred to the buffer pool as
they might be shared between sockets (and the buffer pool cannot be
created until we know what we are binding to). So, before the buffer
pool is created, these two rings are cleaned up with the socket, and
after they have been transferred they are cleaned up together with
the buffer pool.

The problem is that ownership was transferred before it was absolutely
certain that the buffer pool could be created and initialized
correctly and when one of these errors occurred, the fill and
completion rings did neither belong to the socket nor the pool and
where therefore leaked. Solve this by moving the ownership transfer
to the point where the buffer pool has been completely set up and
there is no way it can fail.

Fixes: 7361f9c3d719 ("xsk: Move fill and completion rings to buffer pool")
Reported-by: syzbot+cfa88ddd0655afa88763@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Björn Töpel <bjorn.topel@xxxxxxxxx>
Link: https://lore.kernel.org/bpf/20201214085127.3960-1-magnus.karlsson@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/xdp/xsk.c           |    4 ++++
 net/xdp/xsk_buff_pool.c |    2 --
 2 files changed, 4 insertions(+), 2 deletions(-)

--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -772,6 +772,10 @@ static int xsk_bind(struct socket *sock,
 		}
 	}
 
+	/* FQ and CQ are now owned by the buffer pool and cleaned up with it. */
+	xs->fq_tmp = NULL;
+	xs->cq_tmp = NULL;
+
 	xs->dev = dev;
 	xs->zc = xs->umem->zc;
 	xs->queue_id = qid;
--- a/net/xdp/xsk_buff_pool.c
+++ b/net/xdp/xsk_buff_pool.c
@@ -75,8 +75,6 @@ struct xsk_buff_pool *xp_create_and_assi
 
 	pool->fq = xs->fq_tmp;
 	pool->cq = xs->cq_tmp;
-	xs->fq_tmp = NULL;
-	xs->cq_tmp = NULL;
 
 	for (i = 0; i < pool->free_heads_cnt; i++) {
 		xskb = &pool->heads[i];