• Guillaume Nault's avatar
    l2tp: pass tunnel pointer to ->session_create() · f026bc29
    Guillaume Nault authored
    Using l2tp_tunnel_find() in pppol2tp_session_create() and
    l2tp_eth_create() is racy, because no reference is held on the
    returned session. These functions are only used to implement the
    ->session_create callback which is run by l2tp_nl_cmd_session_create().
    Therefore searching for the parent tunnel isn't necessary because
    l2tp_nl_cmd_session_create() already has a pointer to it and holds a
    reference.
    
    This patch modifies ->session_create()'s prototype to directly pass the
    the parent tunnel as parameter, thus avoiding searching for it in
    pppol2tp_session_create() and l2tp_eth_create().
    
    Since we have to touch the ->session_create() call in
    l2tp_nl_cmd_session_create(), let's also remove the useless conditional:
    we know that ->session_create isn't NULL at this point because it's
    already been checked earlier in this same function.
    
    Finally, one might be tempted to think that the removed
    l2tp_tunnel_find() calls were harmless because they would return the
    same tunnel as the one held by l2tp_nl_cmd_session_create() anyway.
    But that tunnel might be removed and a new one created with same tunnel
    Id before the l2tp_tunnel_find() call. In this case l2tp_tunnel_find()
    would return the new tunnel which wouldn't be protected by the
    reference held by l2tp_nl_cmd_session_create().
    
    Fixes: 309795f4 ("l2tp: Add netlink control API for L2TP")
    Fixes: d9e31d17 ("l2tp: Add L2TP ethernet pseudowire support")
    Signed-off-by: 's avatarGuillaume Nault <g.nault@alphalink.fr>
    Signed-off-by: 's avatarDavid S. Miller <davem@davemloft.net>
    f026bc29
l2tp_netlink.c 26.8 KB