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Date:   Thu, 26 Oct 2017 20:15:55 +0800
From:   Jason Wang <>
Cc:, Jason Wang <>,
        Eric Dumazet <>,
        Willem de Bruijn <>,
        Dmitry Vyukov <>,
        Mark Rutland <>
Subject: [PATCH net] tuntap: properly align skb->head before building skb

An unaligned alloc_frag->offset caused by previous allocation will
result an unaligned skb->head. This will lead unaligned
skb_shared_info and then unaligned dataref which requires to be
aligned for accessing on some architecture. Fix this by aligning
alloc_frag->offset before the frag refilling.

Fixes: 0bbd7dad34f8 ("tun: make tun_build_skb() thread safe")
Cc: Eric Dumazet <>
Cc: Willem de Bruijn <>
Cc: Wei Wei <>
Cc: Dmitry Vyukov <>
Cc: Mark Rutland <>
Reported-by: Wei Wei <>
Signed-off-by: Jason Wang <>
- The patch is needed for -stable.
- Wei, can you try this patch to see if it solves your issue?
 drivers/net/tun.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index b9973fb..60e44f2 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1286,6 +1286,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	buflen += SKB_DATA_ALIGN(len + pad);
+	alloc_frag->offset = ALIGN((u64)alloc_frag->offset, TUN_RX_PAD);
 	if (unlikely(!skb_page_frag_refill(buflen, alloc_frag, GFP_KERNEL)))
 		return ERR_PTR(-ENOMEM);

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