netdev - [PATCH bpf-next v2 3/4] xsk: avoid store-tearing when assigning umem

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Message-Id: <20190826061053.15996-4-bjorn.topel@gmail.com>
Date:   Mon, 26 Aug 2019 08:10:52 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com, magnus.karlsson@...il.com,
        bpf@...r.kernel.org, jonathan.lemon@...il.com,
        syzbot+c82697e3043781e08802@...kaller.appspotmail.com,
        hdanton@...a.com, i.maximets@...sung.com
Subject: [PATCH bpf-next v2 3/4] xsk: avoid store-tearing when assigning umem

From: Björn Töpel <bjorn.topel@...el.com>

The umem member of struct xdp_sock is read outside of the control
mutex, in the mmap implementation, and needs a WRITE_ONCE to avoid
potentional store-tearing.

Acked-by: Jonathan Lemon <jonathan.lemon@...il.com>
Fixes: 423f38329d26 ("xsk: add umem fill queue support and mmap")
Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
---
 net/xdp/xsk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 8fafa3ce3ae6..e3e99ee5631b 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -716,7 +716,7 @@ static int xsk_setsockopt(struct socket *sock, int level, int optname,
 
 		/* Make sure umem is ready before it can be seen by others */
 		smp_wmb();
-		xs->umem = umem;
+		WRITE_ONCE(xs->umem, umem);
 		mutex_unlock(&xs->mutex);
 		return 0;
 	}
-- 
2.20.1