• Roopa Prabhu's avatar
    bridge: set is_local and is_static before fdb entry is added to the fdb hashtable · b7af1472
    Roopa Prabhu authored
    Problem Description:
    We can add fdbs pointing to the bridge with NULL ->dst but that has a
    few race conditions because br_fdb_insert() is used which first creates
    the fdb and then, after the fdb has been published/linked, sets
    "is_local" to 1 and in that time frame if a packet arrives for that fdb
    it may see it as non-local and either do a NULL ptr dereference in
    br_forward() or attach the fdb to the port where it arrived, and later
    br_fdb_insert() will make it local thus getting a wrong fdb entry.
    Call chain br_handle_frame_finish() -> br_forward():
    But in br_handle_frame_finish() in order to call br_forward() the dst
    should not be local i.e. skb != NULL, whenever the dst is
    found to be local skb is set to NULL so we can't forward it,
    and here comes the problem since it's running only
    with RCU when forwarding packets it can see the entry before "is_local"
    is set to 1 and actually try to dereference NULL.
    The main issue is that if someone sends a packet to the switch while
    it's adding the entry which points to the bridge device, it may
    dereference NULL ptr. This is needed now after we can add fdbs
    pointing to the bridge.  This poses a problem for
    br_fdb_update() as well, while someone's adding a bridge fdb, but
    before it has is_local == 1, it might get moved to a port if it comes
    as a source mac and then it may get its "is_local" set to 1
    
    This patch changes fdb_create to take is_local and is_static as
    arguments to set these values in the fdb entry before it is added to the
    hash. Also adds null check for port in br_forward.
    
    Fixes: 3741873b
    
     ("bridge: allow adding of fdb entries pointing to the bridge device")
    Reported-by: default avatarNikolay Aleksandrov <nikolay@cumulusnetworks.com>
    Signed-off-by: default avatarRoopa Prabhu <roopa@cumulusnetworks.com>
    Reviewed-by: default avatarNikolay Aleksandrov <nikolay@cumulusnetworks.com>
    Acked-by: default avatarStephen Hemminger <stephen@networkplumber.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    b7af1472