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    SubjectRe: My last word on copy_to_user
    On Sat, Jan 24, 1998 at 12:12:00AM -0600, Michael Elizabeth Chastain wrote:
    > Hi guys,
    >
    > Here is a list of places in 2.1.80 that call copy_to_user and expect
    > it to return -EFAULT, or a negative number, on error. These callers
    > are wrong.
    >
    > I think most, or all, of these places will work correctly as long
    > as the addresses are supplied are valid. In that case copy_to_user
    > returns 0 and every caller accepts 0 as a sign of success.
    >
    [-------------snip-----------------]
    > IOCTL_OUT drivers/cdrom/cdrom.c

    You are right this should be better documented. I thought I had been
    so careful... Bummer! cdrom.c thinks everything is fine only if
    copy_from_user returns 0. This is the Right Thing(tm) I believe, but
    then it directly returns whatever non-zero stuff copy_from_user returns.
    If indeed copy_to_user returns the number of bits that _didn't_ get
    copied, then I suppose I need to change this to do something like:

    #define IOCTL_IN(arg, type, in) { \
    - int ret=copy_from_user(&in, (type *) arg, sizeof in); \
    - if (ret) return ret; }
    + if ( copy_from_user(&in, (type *) arg, sizeof in) ) \
    + return -EFAULT; }

    Is this the same for copy_to_user as well? Should I change:
    #define IOCTL_OUT(arg, type, out) { \
    - int ret=copy_to_user((type *) arg, &out, sizeof out); \
    - if (ret) return ret; }
    + if ( copy_to_user((type *) arg, &out, sizeof out) ) \
    + return -EFAULT; }
    as well?


    -Erik

    --
    Erik B. Andersen Web: http://www.inconnect.com/~andersen/
    email: andersee@debian.org
    --This message was written using 73% post-consumer electrons--

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