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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.

+ 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)) {
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 */
{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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