• David Howells's avatar
    rxrpc: Limit the listening backlog · 0e119b41
    David Howells authored
    Limit the socket incoming call backlog queue size so that a remote client
    can't pump in sufficient new calls that the server runs out of memory.  Note
    that this is partially theoretical at the moment since whilst the number of
    calls is limited, the number of packets trying to set up new calls is not.
    This will be addressed in a later patch.
    If the caller of listen() specifies a backlog INT_MAX, then they get the
    current maximum; anything else greater than max_backlog or anything
    negative incurs EINVAL.
    The limit on the maximum queue size can be set by:
    	echo N >/proc/sys/net/rxrpc/max_backlog
    where 4<=N<=32.
    Further, set the default backlog to 0, requiring listen() to be called
    before we start actually queueing new calls.  Whilst this kind of is a
    change in the UAPI, the caller can't actually *accept* new calls anyway
    unless they've first called listen() to put the socket into the LISTENING
    state - thus the aforementioned new calls would otherwise just sit there,
    eating up kernel memory.  (Note that sockets that don't have a non-zero
    service ID bound don't get incoming calls anyway.)
    Given that the default backlog is now 0, make the AFS filesystem call
    kernel_listen() to set the maximum backlog for itself.
    Possible improvements include:
     (1) Trimming a too-large backlog to max_backlog when listen is called.
     (2) Trimming the backlog value whenever the value is used so that changes
         to max_backlog are applied to an open socket automatically.  Note that
         the AFS filesystem opens one socket and keeps it open for extended
         periods, so would miss out on changes to max_backlog.
     (3) Having a separate setting for the AFS filesystem.
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
misc.c 2.79 KB