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    From
    SubjectRe: [PATCH] new syscall: flink
    Date
    Followup to:  <1049663559.1602.46.camel@dhcp22.swansea.linux.org.uk>
    By author: Alan Cox <alan@lxorguk.ukuu.org.uk>
    In newsgroup: linux.dev.kernel
    >
    > It is actually rather more complicated. Suppose I give you a pipe
    > pair handle. You can flink what was a private object and has no
    > meaning as a name.
    >
    > Suppose I give you a socket what does the call man ?
    >
    > Suppose I give you a handle to an anonymous mapping ?
    >

    -EXDEV

    > Suppose I give you a handle to data, how do you know what disk
    > it belongs to ?

    f_ino->i_sb should give you that information.

    > Suppose I give you an O_RDONLY handle to a file which you then
    > flink and gain write access too ?

    This, I believe, is the real issue. However, we already have that
    problem:

    #include <unistd.h>
    #include <stdlib.h>
    #include <stdio.h>
    #include <fcntl.h>
    #include <limits.h>

    int main(int argc, char *argv[])
    {
    int rfd, wfd;
    char filebuf[PATH_MAX];

    rfd = open("testfile", O_RDONLY|O_CREAT, 0666);
    /* Now rfd is a read-only file descriptor */

    sprintf(filebuf, "/proc/self/fd/%d", rfd);
    wfd = open(filebuf, O_RDWR);
    /* Now wfd is a read-write file descriptor */

    write(wfd, "Tjo fidelittan hatt!\n", 21);

    return 0;
    }


    -hpa
    --
    <hpa@transmeta.com> at work, <hpa@zytor.com> in private!
    "Unix gives you enough rope to shoot yourself in the foot."
    Architectures needed: ia64 m68k mips64 ppc ppc64 s390 s390x sh v850 x86-64
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