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    SubjectRe: [PATCH IPV6 1/1] ipv6: allocate enough headroom in ip6_finish_output2()
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    On 7/7/21 6:42 PM, Jakub Kicinski wrote:
    > On Wed, 7 Jul 2021 08:45:13 -0600 David Ahern wrote:
    >> On 7/7/21 8:04 AM, Vasily Averin wrote:
    >>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
    >>> index ff4f9eb..e5af740 100644
    >>> --- a/net/ipv6/ip6_output.c
    >>> +++ b/net/ipv6/ip6_output.c
    >>> @@ -61,9 +61,24 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
    >>> struct dst_entry *dst = skb_dst(skb);
    >>> struct net_device *dev = dst->dev;
    >>> const struct in6_addr *nexthop;
    >>> + unsigned int hh_len = LL_RESERVED_SPACE(dev);
    >>> struct neighbour *neigh;
    >>> int ret;
    >>>
    >>> + /* Be paranoid, rather than too clever. */
    >>> + if (unlikely(skb_headroom(skb) < hh_len && dev->header_ops)) {
    >>> + struct sk_buff *skb2;
    >>> +
    >>> + skb2 = skb_realloc_headroom(skb, LL_RESERVED_SPACE(dev));
    >>
    >> why not use hh_len here?
    >
    > Is there a reason for the new skb? Why not pskb_expand_head()?


    pskb_expand_head() might crash, if skb is shared.

    We possibly can add a helper, factorizing all this,
    and eventually use pskb_expand_head() if safe.

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