skbuff: in skb_copy_ubufs unclone before releasing zerocopy
skb_copy_ubufs must unclone before it is safe to modify its skb_shared_info with skb_zcopy_clear. Commitb90ddd5687
("skbuff: skb_copy_ubufs must release uarg even without user frags") ensures that all skbs release their zerocopy state, even those without frags. But I forgot an edge case where such an skb arrives that is cloned. The stack does not build such packets. Vhost/tun skbs have their frags orphaned before cloning. TCP skbs only attach zerocopy state when a frag is added. But if TCP packets can be trimmed or linearized, this might occur. Tracing the code I found no instance so far (e.g., skb_linearize ends up calling skb_zcopy_clear if !skb->data_len). Still, it is non-obvious that no path exists. And it is fragile to rely on this. Fixes:b90ddd5687
("skbuff: skb_copy_ubufs must release uarg even without user frags") Signed-off-by: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -1177,12 +1177,12 @@ int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
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int i, new_frags;
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u32 d_off;
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if (!num_frags)
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goto release;
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if (skb_shared(skb) || skb_unclone(skb, gfp_mask))
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return -EINVAL;
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if (!num_frags)
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goto release;
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new_frags = (__skb_pagelen(skb) + PAGE_SIZE - 1) >> PAGE_SHIFT;
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for (i = 0; i < new_frags; i++) {
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page = alloc_page(gfp_mask);
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