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    Subject[PATCH] Allow /dev/{,k}mem to be disabled to prevent kernel from being modified easily

    After being gloriously rootkitted with a program coded by HTB author Martin
    Devera (lots of thanks, devik, your work is appreciated, I suggest you read
    up about Oppenheimer when disclaiming that you are 'just a coder'. The item
    to google on is: "ethics sweetness hydrogen bomb Oppenheimer"), I wrote
    a patch to disable /dev/kmem and /dev/mem, which is harmless on servers
    without X.

    It blocks attempts by rootkits, such as devik's SucKIT, to hide themselves.

    It is not a final solution but it raises the bar a lot. Please apply.

    By default, nothing is changed, but I'd turn this feature on on servers
    without X. Patch:

    --- linux-2.6.0-test1/drivers/char/Kconfig.orig Mon Jul 14 05:29:27 2003
    +++ linux-2.6.0-test1/drivers/char/Kconfig Sun Aug 3 19:55:37 2003
    @@ -1003,5 +1003,20 @@
    out to lunch past a certain margin. It can reboot the system
    or merely print a warning.

    +config MEMORY_ACCESS
    + bool "Allow userspace access to memory"
    + default y
    + help
    + Security paranoid operators may want to disable userspace
    + from accessing raw memory or kernel memory via /dev/mem and
    + /dev/kmem. Some malware hides itself from sight by manipulating
    + the kernel directly via raw memory, disabling this feature
    + gives some protection against rootkits.
    + Answering 'N' generally breaks the X Window System.
    + Answer 'Y' unless you are paranoid about security or don't
    + care about X.

    --- linux-2.6.0-test1/drivers/char/mem.c.orig Sun Aug 3 19:22:29 2003
    +++ linux-2.6.0-test1/drivers/char/mem.c Sun Aug 3 19:34:04 2003
    @@ -608,12 +608,14 @@
    static int memory_open(struct inode * inode, struct file * filp)
    switch (minor(inode->i_rdev)) {
    +#if defined(CONFIG_MEMORY_ACCESS)
    case 1:
    filp->f_op = &mem_fops;
    case 2:
    filp->f_op = &kmem_fops;
    case 3:
    filp->f_op = &null_fops;
    @@ -655,8 +657,10 @@
    umode_t mode;
    struct file_operations *fops;
    } devlist[] = { /* list of minor devices */
    +#if defined(CONFIG_MEMORY_ACCESS)
    {1, "mem", S_IRUSR | S_IWUSR | S_IRGRP, &mem_fops},
    {2, "kmem", S_IRUSR | S_IWUSR | S_IRGRP, &kmem_fops},
    {3, "null", S_IRUGO | S_IWUGO, &null_fops},
    #if defined(CONFIG_ISA) || !defined(__mc68000__)
    {4, "port", S_IRUSR | S_IWUSR | S_IRGRP, &port_fops},

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