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  • David S. Miller's avatar
    [NDISC]: Fix race in generic address resolution · 69cc64d8
    David S. Miller authored
    Frank Blaschka provided the bug report and the initial suggested fix
    for this bug.  He also validated this version of this fix.
    The problem is that the access to neigh->arp_queue is inconsistent, we
    grab references when dropping the lock lock to call
    neigh->ops->solicit() but this does not prevent other threads of
    control from trying to send out that packet at the same time causing
    corruptions because both code paths believe they have exclusive access
    to the skb.
    The best option seems to be to hold the write lock on neigh->lock
    during the ->solicit() call.  I looked at all of the ndisc_ops
    implementations and this seems workable.  The only case that needs
    special care is the IPV4 ARP implementation of arp_solicit().  It
    wants to take neigh->lock as a reader to protect the header entry in
    neigh->ha during the emission of the soliciation.  We can simply
    remove the read lock calls to take care of that since holding the lock
    as a writer at the caller providers a superset of the protection
    afforded by the existing read locking.
    The rest of the ->solicit() implementations don't care whether the
    neigh is locked or not.
    Signed-off-by: default avatarDavid S. Miller <>