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Reptile kernel rootkit details

https://github.com/f0rb1dd3n/Reptile

Not able to tamper file contents while reading byte-by-byte (❗)
Not able to hide all threads and children of hidden (parent) process (❗)

Environment

Linux kernel 2.6.x/3.x/4.x
x86 (sys_call_table search method is x86-only)

Persistency

Boot-time module loading using OS-specific startup files:

/etc/modules (debian/ubuntu)
/etc/rc.modules (redhat/centos/fedora)

Detection evasion

Rootkit is trying to evade from detection by:

hiding files by name
tampering contents of startup files while reading
hiding kernel module by unlinking from module_list

Management interface

Implemented via kill(2) by hooking sys_call_table[__NR_kill] entry. Supported commands are:

hiding/unhiding processes
hiding/unhiding rootkit's module
enabling/disabling of tampering file content function
gaining root priveleges to calling process

Altering system behaviour

Hooking of system calls by patching syscall-handlers in sys_call_table[]:

to write to read-only page CR0/WP technique used (x86-only)
netfilter hook (NF_IP_PRI_FIRST)

Hiding (tampering) of file contents

Filtering of file content while reading by hooking:

sys_call_table[__NR_read]

Hiding of files and directories

Filtering of directory entries by hoocking:

sys_call_table[__NR_getdents]
sys_call_table[__NR_getdents64]

Hiding of processes and process trees

Filtering PID-like numeric entries while listing /proc:

getdents/getdents64 hook used
hidden tasks are marked using task->flags (bit 0x10000000)

Backdoor/shell

Reverse shell spawning by port-knocking-like technique:

ICMP/UDP/TCP port-knocking
spawning root-shell connection to remote host