ptrace_do is a ptrace library designed to simplify syscall injection in Linux.
What is ptrace?
ptrace is the debugging interface provided by the Linux kernel. It allows you to connect to a running process, examine and alter its memory, and change it's runtime state. Unfortunately, it's quite complex and requires a solid understanding of the underlying architecture and OS. ptrace_do was written to allow pentesters access to a simplified interface for injecting syscalls into a target process.
The best introduction to ptrace that I've seen comes in the form of two articles by Pradeep Padala dating back to 2002:
That's awesome! 1337 h4X0rZ rUL3!!
Sorry, no. This isn't an "exploit". This code only uses standard, though not commonly understood, interfaces for process interaction and control. In order to affect a process you don't already own, you will need to have the CAP_SYS_PTRACE capability (i.e. root).
Can I use this on any Linux host?
Currently, ptrace_do will only work on x86_64 Linux. Because it uses the Linux ptrace interface to inject assembly language syscalls into a target process, nothing here is portable. I did try to keep it as modular as possible, and I would consider porting it to another architecture if it became popular enough.
Example: Injecting "exit(42);"
struct ptrace_do *target;
target = ptrace_do_init(TARGET_PID);
ptrace_do_syscall(target, _NR_exit, 42, 0, 0, 0, 0, 0);
Example: Injecting open / dup2 / close calls to hijack stdin / stdout / stderr.
char *buffer;
struct ptrace_do *target;
void *remote_addr;
int fd;
target = ptrace_do_init(TARGET_PID);
buffer = (char *) ptrace_do_malloc(target, BUFF_SIZE);
memset(buffer, 0, BUFF_SIZE);
snprintf(buffer, BUFF_SIZE, "/dev/pts/4");
remote_addr = ptrace_do_push_mem(target, buffer);
fd = ptrace_do_syscall(target, __NR_open, remote_addr, O_RDWR, 0, 0, 0, 0);
ptrace_do_syscall(target, __NR_dup2, fd, 0, 0, 0, 0, 0);
ptrace_do_syscall(target, __NR_dup2, fd, 1, 0, 0, 0, 0);
ptrace_do_syscall(target, __NR_dup2, fd, 2, 0, 0, 0, 0);
ptrace_do_syscall(target, __NR_close, fd, 0, 0, 0, 0, 0);
ptrace_do_cleanup(target);
For a more advanced usage, please examine my shelljack code, for which this library was written to accomidate.
Here is the brief list of function interfaces. These functions are documented in greater detail within the source.
/* ptrace_do_init() hooks the target and prepares it to run our commands. */
struct ptrace_do *ptrace_do_init(int pid);
/* ptrace_do_malloc() allocates memory in the remote process for our use, without worry of upsetting the remote memory state. */
void *ptrace_do_malloc(struct ptrace_do *target, size_t size);
/* ptrace_do_free() frees a joint memory object. "operation" refers to the FREE_* modes above. */
void ptrace_do_free(struct ptrace_do *target, void *local_address, int operation);
/* ptrace_do_push_mem() and ptrace_do_pull_mem() synchronize the memory states between local and remote buffers. */
void *ptrace_do_push_mem(struct ptrace_do *target, void *local_address);
void *ptrace_do_pull_mem(struct ptrace_do *target, void *local_address);
/* Short helper function to translate your local address to the remote one. */
void *ptrace_do_get_remote_addr(struct ptrace_do *target, void *local_addr);
/* ptrace_do_sig_ignore() sets the signal mask for the remote process. */
/* This is simple enough, we only need a macro. */
/* Note, this is for *our* handling of remote signals. This won't persist once we detatch. */
#define ptrace_do_sig_ignore(TARGET, SIGNAL) TARGET->sig_ignore |= 1<<SIGNAL
/* ptrace_do_syscall() will execute the given syscall inside the remote process. */
unsigned long ptrace_do_syscall(struct ptrace_do *target, unsigned long rax, \
unsigned long rdi, unsigned long rsi, unsigned long rdx, unsigned long r10, unsigned long r8, unsigned long r9);
/* ptrace_do_cleanup() will detatch and do it's best to clean up the data structures. */
void ptrace_do_cleanup(struct ptrace_do *target);
/* get_proc_pid_maps() processes the maps file and returns the created object.*/
struct parse_maps *get_proc_pid_maps(pid_t target);
/* free_parse_maps_list() destroys a parse_maps object chain. */
void free_parse_maps_list(struct parse_maps *head);
/* Mostly for debugging, but in case it comes in handy, this function prints the parse_maps object members. */
void dump_parse_maps_list(struct parse_maps *head);
git clone https://github.com/emptymonkey/ptrace_do.git
cd ptrace_do
make
I write and release these tools with the intention of educating the larger IT community and empowering legitimate pentesters. If I can write these tools in my spare time, then rest assured that the dedicated malicious actors have already developed versions of their own.
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