Fwd: net/ipx: null-ptr-deref in ipxrtr_route_packet

From: Andrey Konovalov
Date: Mon Oct 24 2016 - 10:23:02 EST

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+acme@xxxxxxxxxx

Hi,

I've got the following error report while running the syzkaller fuzzer:

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Modules linked in:
CPU: 0 PID: 3953 Comm: syz-executor Not tainted 4.9.0-rc1+ #228
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88006aa2ac00 task.stack: ffff880068a90000
RIP: 0010:[<ffffffff834ed8f4>] [<ffffffff834ed8f4>]
ipxrtr_route_packet+0x4e4/0xbe0 net/ipx/ipx_route.c
:213
RSP: 0018:ffff880068a97b08 EFLAGS: 00010246
RAX: ffff88006b648500 RBX: ffff880068a97e40 RCX: dffffc0000000000
RDX: 0000000000000003 RSI: 0000000000000000 RDI: ffff88006b648960
RBP: ffff880068a97bc8 R08: dffffc0000000000 R09: 1ffff1000d4ddf97
R10: dffffc0000000000 R11: 0000000000000000 R12: ffff88006b410300
R13: 0000000000000000 R14: ffff88006444b68e R15: ffff88006a6efc80
FS: 00007f28cf665700(0000) GS:ffff88006cc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000451f80 CR3: 0000000068a9a000 CR4: 00000000000006f0
Stack:
ffff88006a6efd58 ffff880068a97dc0 ffff880068a97e44 1ffff1000d152f68
000000000000001a 0000000000000000 ffff88006b648500 0000000041b58ab3
ffffffff847fb90b ffffffff834ed410 ffffffff82b7cfea ffff8800ffffff97
Call Trace:
[<ffffffff834e802e>] ipx_sendmsg+0x30e/0x550 net/ipx/af_ipx.c:1749
[< inline >] sock_sendmsg_nosec net/socket.c:606
[<ffffffff82b7075c>] sock_sendmsg+0xcc/0x110 net/socket.c:616
[<ffffffff82b718a1>] SYSC_sendto+0x211/0x340 net/socket.c:1641
[<ffffffff82b73e80>] SyS_sendto+0x40/0x50 net/socket.c:1609
[<ffffffff83fc0141>] entry_SYSCALL_64_fastpath+0x1f/0xc2
arch/x86/entry/entry_64.S:209
Code: 41 80 7c 0d 00 00 0f 85 82 06 00 00 48 8b 85 70 ff ff ff 49 b8
00 00 00 00 00 fc ff df 4c 8b a8 60 04 00 00 4c 89 ee 48 c1 ee 03 <46>
0f b6 0c 06 45 84 c9 74 0a 41 80 f9 03 0f 8e e5 05 00 00 49
RIP [<ffffffff834ed8f4>] ipxrtr_route_packet+0x4e4/0xbe0
net/ipx/ipx_route.c:213
RSP <ffff880068a97b08>
---[ end trace f5bc9a28de6b2776 ]---
==================================================================

For some reason ipxs->intrfc ends up being NULL.

The reproducer is attached, you need to run a few instances simultaneously.

In case it's relevant, this is what I have in /etc/network/interfaces:

auto eth1
iface eth1 inet static
address 192.168.1.5
netmask 255.255.255.0
post-up arp -s 192.168.1.6 aa:aa:aa:aa:aa:aa
iface eth1 ipx static
frame EtherII
netnum 0x42424242

On commit 1a1891d762d6e64daf07b5be4817e3fbb29e3c59 (Oct 18).
// autogenerated by syzkaller (http://github.com/google/syzkaller)

#ifndef __NR_sendto
#define __NR_sendto 44
#endif
#ifndef __NR_syz_fuse_mount
#define __NR_syz_fuse_mount 1000004
#endif
#ifndef __NR_syz_open_dev
#define __NR_syz_open_dev 1000002
#endif
#ifndef __NR_syz_test
#define __NR_syz_test 1000001
#endif
#ifndef __NR_mmap
#define __NR_mmap 9
#endif
#ifndef __NR_socket
#define __NR_socket 41
#endif
#ifndef __NR_bind
#define __NR_bind 49
#endif
#ifndef __NR_syz_fuseblk_mount
#define __NR_syz_fuseblk_mount 1000005
#endif
#ifndef __NR_syz_open_pts
#define __NR_syz_open_pts 1000003
#endif

#include <fcntl.h>
#include <pthread.h>
#include <setjmp.h>
#include <signal.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

__thread int skip_segv;
__thread jmp_buf segv_env;

static void segv_handler(int sig, siginfo_t* info, void* uctx)
{
if (__atomic_load_n(&skip_segv, __ATOMIC_RELAXED))
_longjmp(segv_env, 1);
exit(sig);
}

static void install_segv_handler()
{
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_sigaction = segv_handler;
sa.sa_flags = SA_NODEFER | SA_SIGINFO;
sigaction(SIGSEGV, &sa, NULL);
sigaction(SIGBUS, &sa, NULL);
}

#define NONFAILING(...) \
{ \
__atomic_fetch_add(&skip_segv, 1, __ATOMIC_SEQ_CST); \
if (_setjmp(segv_env) == 0) { \
__VA_ARGS__; \
} \
__atomic_fetch_sub(&skip_segv, 1, __ATOMIC_SEQ_CST); \
}

static uintptr_t syz_open_dev(uintptr_t a0, uintptr_t a1, uintptr_t a2)
{
if (a0 == 0xc || a0 == 0xb) {
char buf[128];
sprintf(buf, "/dev/%s/%d:%d", a0 == 0xc ? "char" : "block",
(uint8_t)a1, (uint8_t)a2);
return open(buf, O_RDWR, 0);
} else {
char buf[1024];
char* hash;
strncpy(buf, (char*)a0, sizeof(buf));
buf[sizeof(buf) - 1] = 0;
while ((hash = strchr(buf, '#'))) {
*hash = '0' + (char)(a1 % 10);
a1 /= 10;
}
return open(buf, a2, 0);
}
}

static uintptr_t syz_open_pts(uintptr_t a0, uintptr_t a1)
{
int ptyno = 0;
if (ioctl(a0, TIOCGPTN, &ptyno))
return -1;
char buf[128];
sprintf(buf, "/dev/pts/%d", ptyno);
return open(buf, a1, 0);
}

static uintptr_t syz_fuse_mount(uintptr_t a0, uintptr_t a1,
uintptr_t a2, uintptr_t a3,
uintptr_t a4, uintptr_t a5)
{
uint64_t target = a0;
uint64_t mode = a1;
uint64_t uid = a2;
uint64_t gid = a3;
uint64_t maxread = a4;
uint64_t flags = a5;

int fd = open("/dev/fuse", O_RDWR);
if (fd == -1)
return fd;
char buf[1024];
sprintf(buf, "fd=%d,user_id=%ld,group_id=%ld,rootmode=0%o", fd,
(long)uid, (long)gid, (unsigned)mode & ~3u);
if (maxread != 0)
sprintf(buf + strlen(buf), ",max_read=%ld", (long)maxread);
if (mode & 1)
strcat(buf, ",default_permissions");
if (mode & 2)
strcat(buf, ",allow_other");
syscall(SYS_mount, "", target, "fuse", flags, buf);
return fd;
}

static uintptr_t syz_fuseblk_mount(uintptr_t a0, uintptr_t a1,
uintptr_t a2, uintptr_t a3,
uintptr_t a4, uintptr_t a5,
uintptr_t a6, uintptr_t a7)
{
uint64_t target = a0;
uint64_t blkdev = a1;
uint64_t mode = a2;
uint64_t uid = a3;
uint64_t gid = a4;
uint64_t maxread = a5;
uint64_t blksize = a6;
uint64_t flags = a7;

int fd = open("/dev/fuse", O_RDWR);
if (fd == -1)
return fd;
if (syscall(SYS_mknodat, AT_FDCWD, blkdev, S_IFBLK, makedev(7, 199)))
return fd;
char buf[256];
sprintf(buf, "fd=%d,user_id=%ld,group_id=%ld,rootmode=0%o", fd,
(long)uid, (long)gid, (unsigned)mode & ~3u);
if (maxread != 0)
sprintf(buf + strlen(buf), ",max_read=%ld", (long)maxread);
if (blksize != 0)
sprintf(buf + strlen(buf), ",blksize=%ld", (long)blksize);
if (mode & 1)
strcat(buf, ",default_permissions");
if (mode & 2)
strcat(buf, ",allow_other");
syscall(SYS_mount, blkdev, target, "fuseblk", flags, buf);
return fd;
}

static uintptr_t execute_syscall(int nr, uintptr_t a0, uintptr_t a1,
uintptr_t a2, uintptr_t a3,
uintptr_t a4, uintptr_t a5,
uintptr_t a6, uintptr_t a7,
uintptr_t a8)
{
switch (nr) {
default:
return syscall(nr, a0, a1, a2, a3, a4, a5);
case __NR_syz_test:
return 0;
case __NR_syz_open_dev:
return syz_open_dev(a0, a1, a2);
case __NR_syz_open_pts:
return syz_open_pts(a0, a1);
case __NR_syz_fuse_mount:
return syz_fuse_mount(a0, a1, a2, a3, a4, a5);
case __NR_syz_fuseblk_mount:
return syz_fuseblk_mount(a0, a1, a2, a3, a4, a5, a6, a7);
}
}

long r[18];

int main()
{
install_segv_handler();
memset(r, -1, sizeof(r));
r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0xe000ul, 0x3ul,
0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
r[1] = execute_syscall(__NR_socket, 0x4ul, 0x2ul, 0x0ul, 0, 0, 0, 0,
0, 0);
r[2] = execute_syscall(__NR_mmap, 0x2000e000ul, 0x1000ul, 0x3ul,
0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
NONFAILING(*(uint16_t*)0x2000e000 = (uint16_t)0x2);
NONFAILING(*(uint16_t*)0x2000e002 = (uint16_t)0x4242);
NONFAILING(*(uint32_t*)0x2000e004 = (uint32_t)0x0);
NONFAILING(*(uint8_t*)0x2000e008 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000e009 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000e00a = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000e00b = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000e00c = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000e00d = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000e00e = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000e00f = (uint8_t)0x0);
r[14] = execute_syscall(__NR_bind, r[1], 0x2000e000ul, 0x10ul, 0, 0,
0, 0, 0, 0);
NONFAILING(memcpy((void*)0x20007fe6, "\xae\x89\xfa\x41\xd0\x29\x69"
"\xc3\xac\x79\xf0\x64\xc6\xad"
"\x6b\x27\x63\x6b\x49\x0d\x99"
"\x7b\x01\x9e\x3e\xb3",
26));
NONFAILING(memcpy(
(void*)0x2000d000,
"\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00",
128));
r[17] = execute_syscall(__NR_sendto, r[1], 0x20007fe6ul, 0x1aul,
0x0ul, 0x2000d000ul, 0x80ul, 0, 0, 0);
return 0;
}

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