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    SubjectRe: AUDIT: copy_from_user is a deathtrap.
    Date
    In message <Pine.LNX.4.44.0205191125120.3104-100000@home.transmeta.com> you wri
    te:
    >
    >
    > On Sat, 18 May 2002, Benjamin Herrenschmidt wrote:
    > >
    > > Looking at generic_file_write(), it ignore the count returned by
    > > copy_from_user and always commit a write for the whole requested
    > > count, regardless of how much could actually be read from userland.
    > > The result of copy_from_user is only used as an error condition.
    >
    > And this is exactly what makes it re-startable.

    If read always returns the amount read (ignoring any copy_to_user
    errors), then you can repeat it by seeking backwards[1] and redoing the
    read.

    So copy_to_user can simply deliver a SIGSEGV and return "success", and
    everything will work (except sockets, pipes, etc).

    Is this satisfactory? I'd really like to get rid of 5,500 code paths
    in the kernel...

    BTW, SuSv3/POSIX.1.2001 says it's OK,
    Rusty.
    [1] No, this won't work on pipes & sockets, but the whole idea won't
    work on many devices anyway...
    --
    Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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