net/netlink: null-ptr-deref in netlink_dump/lock_acquire

From: Andrey Konovalov
Date: Wed Oct 19 2016 - 12:26:38 EST

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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: 1 PID: 3933 Comm: syz-executor Not tainted 4.9.0-rc1+ #230
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88006b79d800 task.stack: ffff88006bbc0000
RIP: 0010:[<ffffffff8120872d>] [<ffffffff8120872d>]
__lock_acquire+0x12d/0x3450 kernel/locking/lockdep.c:3221
RSP: 0018:ffff88006bbc7420 EFLAGS: 00010006
RAX: 0000000000000046 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: 000000000000000c RSI: 0000000000000000 RDI: 0000000000000003
RBP: ffff88006bbc75c0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff85f42240 R12: ffff88006b79d800
R13: ffffffff84bfe4e0 R14: 0000000000000001 R15: 0000000000000060
FS: 00007fd9c41cc700(0000) GS:ffff88006cd00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000451f80 CR3: 00000000638f0000 CR4: 00000000000006e0
Stack:
0000000000000000 ffff88006bbc0000 ffff88006bbc8000 0000000000000000
0000000000000002 ffff88006b79d800 0000000000000000 ffff88006bbc7f48
ffffffff852adc60 0000000000000000 ffffffff852adc64 1ffffffff0b40135
Call Trace:
[<ffffffff8120c5ae>] lock_acquire+0x17e/0x340 kernel/locking/lockdep.c:3746
[< inline >] __mutex_lock_common kernel/locking/mutex.c:521
[<ffffffff83fb6fe1>] mutex_lock_nested+0xb1/0x890 kernel/locking/mutex.c:621
[<ffffffff82db6fd0>] netlink_dump+0x50/0xac0 net/netlink/af_netlink.c:2067
[<ffffffff82dba381>] __netlink_dump_start+0x501/0x770
net/netlink/af_netlink.c:2200
[<ffffffff82dc35b2>] genl_family_rcv_msg+0xa02/0xc80
net/netlink/genetlink.c:595
[<ffffffff82dc39e6>] genl_rcv_msg+0x1b6/0x270 net/netlink/genetlink.c:658
[<ffffffff82dc1a70>] netlink_rcv_skb+0x2c0/0x3b0 net/netlink/af_netlink.c:2281
[<ffffffff82dc2b98>] genl_rcv+0x28/0x40 net/netlink/genetlink.c:669
[< inline >] netlink_unicast_kernel net/netlink/af_netlink.c:1214
[<ffffffff82dc0329>] netlink_unicast+0x5a9/0x880 net/netlink/af_netlink.c:1240
[<ffffffff82dc0fb7>] netlink_sendmsg+0x9b7/0xce0 net/netlink/af_netlink.c:1786
[< inline >] sock_sendmsg_nosec net/socket.c:606
[<ffffffff82b7075c>] sock_sendmsg+0xcc/0x110 net/socket.c:616
[<ffffffff82b709c1>] sock_write_iter+0x221/0x3b0 net/socket.c:814
[< inline >] new_sync_write fs/read_write.c:499
[<ffffffff8151c944>] __vfs_write+0x334/0x570 fs/read_write.c:512
[<ffffffff8152045b>] vfs_write+0x17b/0x500 fs/read_write.c:560
[< inline >] SYSC_write fs/read_write.c:607
[<ffffffff81523d84>] SyS_write+0xd4/0x1a0 fs/read_write.c:599
[<ffffffff83fc0141>] entry_SYSCALL_64_fastpath+0x1f/0xc2
arch/x86/entry/entry_64.S:209
Code: 0f 1f 44 00 00 f6 c4 02 0f 85 24 0a 00 00 44 8b 35 c9 61 8b 03
45 85 f6 74 2c 4c 89 fa 48 bb 00 00 00 00 00 fc ff df 48 c1 ea 03 <80>
3c 1a 00 0f 85 04 2f 00 00 49 81 3f a0 dc 2a 85 41 be 00 00
RIP [<ffffffff8120872d>] __lock_acquire+0x12d/0x3450
kernel/locking/lockdep.c:3221
RSP <ffff88006bbc7420>
---[ end trace 685b3c182bf7f25c ]---

The reproducer is attached.

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

#ifndef __NR_syz_test
#define __NR_syz_test 1000001
#endif
#ifndef __NR_socket
#define __NR_socket 41
#endif
#ifndef __NR_write
#define __NR_write 1
#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_mmap
#define __NR_mmap 9
#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[4];

int main()
{
install_segv_handler();
memset(r, -1, sizeof(r));
r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0x9bc000ul, 0x3ul,
0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
r[1] = execute_syscall(__NR_socket, 0x10ul, 0x3ul, 0x10ul, 0, 0, 0, 0,
0, 0);
NONFAILING(memcpy((void*)0x2061a000,
"\x1f\x00\x00\x00\x24\x00\x07\x83\xf9\xff\xff\xff"
"\xff\xff\xff\xff\x03\x00\x09\x0a\x45\x58\xe2\x93"
"\x3e\x00\x03\x92\x04\x00\x1c\x18\x08\x00\xf3\x01"
"\x97\x68\x1a",
39));
r[3] = execute_syscall(__NR_write, r[1], 0x2061a000ul, 0x27ul, 0, 0,
0, 0, 0, 0);
return 0;
}

Next message: Michal Hocko: "Re: [PATCH] proc: fix NULL dereference when reading /proc/<pid>/auxv"
Previous message: SF Markus Elfring: "Re: [media] winbond-cir: Move a variable assignment in wbcir_tx()"
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