Intruducer

The intruder introducer!

A Rust crate to load a shared library into a Linux process without using ptrace. This is a portable rewrite of dlinject.

Compatibility

It should work for x86, x86-64, arm and aarch64, for both Linux and Android.

Example

# Build binary
cargo build --example intruducer
# Build victim
cargo build --example victim
# Build library
rustc ./examples/evil.rs --crate-type cdylib --out-dir ./target/debug/examples

# Execute the victim
cd ./target/debug/examples
./victim

# Within a new shell
cd ./target/debug/examples
./intruducer -l ./libevil.so `pidof victim`

How it works

1. Retrieve the instruction pointer (ip) of the target process reading /proc/<pid>/syscall;
2. Open /proc/<pid>/mem and backs up the content at ip;
3. Generate the two payloads, and saves the last one to a file.
4. Write the first payload to the target process memory at ip - the execution flow is now altered.
5. The first payload loads and executes the second payload.
6. The second payload restores the original code, calls dlopen and branches to ip - the original execution flow is resumed.

Caveats

• It makes large applications crash when a lot of computing is going on - this happens when a thread is executing the first payload and another one is executing the second payload, which restores the original code. A possible solution consists in freezing every thread but one using /sys/fs/cgroup/freezer, let this one perform the whole task and then thawing all the others. However, this only seemed to reduce the chance of crashes.
• A register (x28) will be clobbered on aarch64 - I found no way to branch to an absolute virtual address without using a register.
• When targeting an Android application, both library and second payload binary blob will be copied to its native library directory - changing the security context to u:object_r:apk_data_file:s0 is not enough for the library file.