• Eric W. Biederman's avatar
    [NET]: Fix race when opening a proc file while a network namespace is exiting. · 077130c0
    Eric W. Biederman authored
    The problem:  proc_net files remember which network namespace the are
    against but do not remember hold a reference count (as that would pin
    the network namespace).   So we currently have a small window where
    the reference count on a network namespace may be incremented when opening
    a /proc file when it has already gone to zero.
    
    To fix this introduce maybe_get_net and get_proc_net.
    
    maybe_get_net increments the network namespace reference count only if it is
    greater then zero, ensuring we don't increment a reference count after it
    has gone to zero.
    
    get_proc_net handles all of the magic to go from a proc inode to the network
    namespace instance and call maybe_get_net on it.
    
    PROC_NET the old accessor is removed so that we don't get confused and use
    the wrong helper function.
    
    Then I fix up the callers to use get_proc_net and handle the case case
    where get_proc_net returns NULL.  In that case I return -ENXIO because
    effectively the network namespace has already gone away so the files
    we are trying to access don't exist anymore.
    Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
    Acked-by: default avatarPaul E. McKenney <paulmck@us.ibm.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    077130c0
af_netlink.c 44.7 KB