fl/main.c

#include <stdint.h>
#include <sys/syscall.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

extern void cat(int fd, long sz);

#ifndef __FreeBSD__
#include <sys/prctl.h>
#define SYSCT_FBSD 588

uint8_t sel = SYSCALL_DISPATCH_FILTER_ALLOW;

uint16_t scmap[SYSCT_FBSD] = {
	-1, // SYS_syscall needs args shifted
	SYS_exit,
	-1, // SYS_fork needs sud reset
	SYS_read,
	SYS_write,
	SYS_open,
	SYS_close,
	-1, // wait4
	-1, // [old] creat
	SYS_link,
	SYS_unlink,
	-1, // [obsolete] execv
	SYS_chdir,
	SYS_fchdir,
	-1, // [freebsd11] mknod
	SYS_chmod,
	SYS_chown,
	-1, // break (no manual)
	-1, // [freebsd4] getfsstat
	-1, // [old] lseek
	SYS_getpid,
};

// TODO also create trampoline for freebsd native signals
void systrap(int n, siginfo_t* s, ucontext_t* c) {
	sel = SYSCALL_DISPATCH_FILTER_ALLOW;
	if(s->si_code != /* SYS_USER_DISPATCH - value from <asm-generic/siginfo.h> */ 2) {
		// TODO chain old syscall handler
	} else if(s->si_syscall > SYSCT_FBSD-1) {
		// TODO fail - check how freebsd does this, esp. with nosys entries
	} else if(scmap[s->si_syscall] == -1) {
		switch(s->si_syscall) {
			default:
				abort();
				break;
		}
	}
	// TODO find max arg ct. and check stack if needed
	c->uc_mcontext.gregs[13] = syscall(
		scmap[s->si_syscall],
		c->uc_mcontext.gregs[8],	
		c->uc_mcontext.gregs[9],	
		c->uc_mcontext.gregs[12]	
	);
	//for(int i = 0; i < 23; i++) printf("%i: %lX\n", i, c->uc_mcontext.gregs[i]);
	sel = SYSCALL_DISPATCH_FILTER_BLOCK;
}
#endif

typedef struct {
	uint8_t magic[4];
	uint8_t bits;
	uint8_t endian;
	uint8_t hdrver;
	uint8_t abi;
	uint8_t pad[8];
	uint16_t type;
	uint16_t isa;
	uint32_t ver;
	uint64_t ep;
	uint64_t phtable;
	uint64_t shtable;
	uint32_t flags;
	uint16_t hsz;
	uint16_t phtesz;
	uint16_t phtct;
	uint16_t shtesz;
	uint16_t shtct;
	uint16_t nameind;
} __attribute__((packed)) elf;

#ifndef __FreeBSD__
char** getmaps(int* tsz) {
	int fd = open("/proc/self/maps", O_RDONLY);
	char c;
	*tsz = 0;
	int p = 0, s = 128;
	char** t = malloc(sizeof(char*));
	t[0] = malloc(s);
	while(read(fd, &c, 1)) {
		if(c == '\n') c = 0;
		t[*tsz][p++] = c;
		if(p >= s) t[*tsz] = realloc(t[*tsz], s += 8);
		if(!c) {
			t = realloc(t, ((++(*tsz)) + 1) * sizeof(char*));
			t[*tsz] = malloc(s = 128);
			p = 0;
		}
	}
	(*tsz)++;
	close(fd);
	return t;
}

typedef struct {
	uint64_t start;
	uint64_t len;
	uint8_t rwx;
	char* name;
} map;

void stomap(char* s, map* m) {
	m->start = 0;
	m->len = 0;
	m->rwx = 0;
	while(*s != '-') {
		m->start <<= 4;
		if(*s >= '0' && *s <= '9') m->start |= *s - '0';
		else m->start |= *s - 'a' + 10;
		s++;
	}
	s++;
	while(*s != ' ') {
		m->len <<= 4;
		if(*s >= '0' && *s <= '9') m->len |= *s - '0';
		else m->len |= *s - 'a' + 10;
		s++;
	}
	s++;
	for(int i = 0; i < 3; i++) {
		m->rwx <<= 1;
		m->rwx |= (*(s++) != '-');
	}
	s += 2;
	while(*(s++) != ':');
	while(*(s++) != ' ');
	while(*s >= '0' && *s <= '9') s++;
	while(*(++s) == ' ');
	int d = strlen(s) + 1;
	m->name = memcpy(malloc(d), s, d);
	m->len -= m->start;
}
#endif

int main(int argc, char** argv) {
#ifndef __FreeBSD__
	struct sigaction a, oa;
	sigemptyset(&a.sa_mask);
	a.sa_flags = SA_SIGINFO;
	a.sa_sigaction = (void(*)(int, siginfo_t*, void*))systrap;

	int nm;
	char** smaps = getmaps(&nm);

	for(int i = 0; i < nm-1; i++) if(strstr(smaps[i], "libc")) {
		map rmap;
		stomap(smaps[i], &rmap);
		if(rmap.rwx & 1) prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, rmap.start, rmap.len, &sel);
	}
	for(int i = 0; i < nm; i++) free(smaps[i]);
	free(smaps);
#endif

	if(argc < 2) return printf("no file provided\n");
	int fd = open(argv[1], O_RDONLY);
	struct stat s;
	fstat(fd, &s);
#ifndef __FreeBSD__
	sigaction(SIGSYS, &a, &oa);
	sel = SYSCALL_DISPATCH_FILTER_BLOCK;
#endif
	cat(fd, s.st_size);
}