Re: [PATCH] Kconfig: Make config Filter access to /dev/mem default y

[Xiaotian Feng <xtfeng@gmail.com>]

On Thu, Apr 15, 2010 at 2:17 PM, wzt wzt <wzt.wzt@gmail.com> wrote:
> On Thu, Apr 15, 2010 at 2:12 PM, Xiaotian Feng <xtfeng@gmail.com> wrote:
>> On Tue, Apr 13, 2010 at 10:52 AM,  <wzt.wzt@gmail.com> wrote:
>>> Recently, most company start use >=2.6.31 kernels to replace redhat kernels.
>>> But the config "Filter access to /dev/mem" is "default n", that allows kernel
>>> rootkit using /dev/mem again. it could access all kernel memory default. Most
>>> administrator don't known the "Filter access to /dev/mem" is "defult N", when
>>> he compiles the kernel, it's easily to be attacked by rootkit.
>>
>> Have you ever successfully attack by this way?
>
> [root@localhost zealot]# ./zealot

so you're running rootkit as a root user?

> [+] Found HISTSIZE.                             [SAFE]
> [+] Check md5 values.                           [SAFE]
> [+] eth0 was not set promsic.                   [SAFE]
> [+] Not found raw socket.                       [SAFE]
> system_call addr changed to 0xc04028a0,sys_call_table addr changed to
> 0xc0675130,Found dr rootkit!,system call sys_execve addr changed to
> 0xc0401582,system call sys_olduname addr changed to 0xc0405989,system
> call sys_fork addr changed to 0xc0407bbb
>
> It's a host ids i wrote,  it could search all kernel memory using /dev/mem. ok?
>
> some of the code here:
> static void *kmap(unsigned long off, unsigned long count)
> {
>        int fd;
>        void *p;
>
>        fd = open(DEV_MEM, O_RDWR);
>        if (fd < 3) {
>                DbgPrint("open %s failed.\n", DEV_MEM);
>                dup2(fd, 3);
>                close(fd);
>                fd = 3;
>        }
>
>        p = mmap(NULL, ALIGNUP(count + 4097), PROT_READ | PROT_WRITE,
>                MAP_SHARED, fd, ALIGNDOWN(off) & 0x0fffffff);
>        if (p == MAP_FAILED)
>        {
>                mem_support_flag = 1;
>                fprintf(stdout, "[-] /dev/mem cannot be read or write.\n");
>
>                DbgPrint("mmap failture, errno %d\n", errno);
>                close(fd);
>                return NULL;
>        }
>
>        close(fd);
>        return p;
> }
>
>>If CONFIG_STRICT_DEVMEM
>> is not set, the /dev/mem access is filtered in pat code.
> please point it, thanks.
>

Years ago, someone sent the same patch.
check http://lkml.org/lkml/2008/11/7/361

>>>
>>> Signed-off-by: Zhitong Wang <zhitong.wangzt@alibaba-inc.com>
>>>
>>> ---
>>>  arch/x86/Kconfig.debug            |    3 ++-
>>>  arch/x86/configs/i386_defconfig   |    2 +-
>>>  arch/x86/configs/x86_64_defconfig |    2 +-
>>>  3 files changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
>>> index bc01e3e..733aea6 100644
>>> --- a/arch/x86/Kconfig.debug
>>> +++ b/arch/x86/Kconfig.debug
>>> @@ -7,6 +7,7 @@ source "lib/Kconfig.debug"
>>>
>>>  config STRICT_DEVMEM
>>>        bool "Filter access to /dev/mem"
>>> +       default y
>>>        ---help---
>>>          If this option is disabled, you allow userspace (root) access to all
>>>          of memory, including kernel and userspace memory. Accidental
>>> @@ -20,7 +21,7 @@ config STRICT_DEVMEM
>>>          This is sufficient for dosemu and X and all common users of
>>>          /dev/mem.
>>>
>>> -         If in doubt, say Y.
>>> +         If in doubt, say N.
>>>
>>>  config X86_VERBOSE_BOOTUP
>>>        bool "Enable verbose x86 bootup info messages"
>>> diff --git a/arch/x86/configs/i386_defconfig b/arch/x86/configs/i386_defconfig
>>> index d28fad1..95c85a8 100644
>>> --- a/arch/x86/configs/i386_defconfig
>>> +++ b/arch/x86/configs/i386_defconfig
>>> @@ -2386,7 +2386,7 @@ CONFIG_PROVIDE_OHCI1394_DMA_INIT=y
>>>  # CONFIG_SAMPLES is not set
>>>  CONFIG_HAVE_ARCH_KGDB=y
>>>  # CONFIG_KGDB is not set
>>> -# CONFIG_STRICT_DEVMEM is not set
>>> +CONFIG_STRICT_DEVMEM=y
>>>  CONFIG_X86_VERBOSE_BOOTUP=y
>>>  CONFIG_EARLY_PRINTK=y
>>>  CONFIG_EARLY_PRINTK_DBGP=y
>>> diff --git a/arch/x86/configs/x86_64_defconfig b/arch/x86/configs/x86_64_defconfig
>>> index 6c86acd..659bfe7 100644
>>> --- a/arch/x86/configs/x86_64_defconfig
>>> +++ b/arch/x86/configs/x86_64_defconfig
>>> @@ -2360,7 +2360,7 @@ CONFIG_PROVIDE_OHCI1394_DMA_INIT=y
>>>  # CONFIG_SAMPLES is not set
>>>  CONFIG_HAVE_ARCH_KGDB=y
>>>  # CONFIG_KGDB is not set
>>> -# CONFIG_STRICT_DEVMEM is not set
>>> +CONFIG_STRICT_DEVMEM=y
>>>  CONFIG_X86_VERBOSE_BOOTUP=y
>>>  CONFIG_EARLY_PRINTK=y
>>>  CONFIG_EARLY_PRINTK_DBGP=y
>>> --
>>> 1.6.5.3
>>>
>>> --
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>>
>