net/udp: bug in skb_pull_rcsum

From: Andrey Konovalov
Date: Tue Nov 22 2016 - 06:58:58 EST

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Hi,

I've got the following error report while fuzzing the kernel with syzkaller.

A reproducer is attached.

On commit 9c763584b7c8911106bb77af7e648bef09af9d80 (4.9-rc6, Nov 20).

------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:3029!
invalid opcode: 0000 [#1] SMP KASAN
Modules linked in:
CPU: 1 PID: 3854 Comm: a.out Not tainted 4.9.0-rc6+ #431
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff880068472c00 task.stack: ffff880063ec8000
RIP: 0010:[<ffffffff82b8fd85>] [<ffffffff82b8fd85>]
skb_pull_rcsum+0x255/0x350 net/core/skbuff.c:3029
RSP: 0018:ffff880063ecf660 EFLAGS: 00010297
RAX: ffff880068472c00 RBX: ffff880065a2da00 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 000000000000000d RDI: ffffed000c7d9ec0
RBP: ffff880063ecf690 R08: 1ffff1000d08e67e R09: 1ffff1000cb45b50
R10: dffffc0000000000 R11: 0000000000000000 R12: ffff880065a2da80
R13: 0000000000000008 R14: ffff880065a2dad8 R15: 0000000000000001
FS: 00007fbb006497c0(0000) GS:ffff88006cd00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020032fe0 CR3: 00000000636d9000 CR4: 00000000000006e0
Stack:
ffff88006bfbb948 ffff880065a2da00 ffff880064160000 1ffff1000cb45b52
0000000000000000 1ffff1000d4d3933 ffff880063ecf6f8 ffffffff83354ced
00000000fffffe00 ffff880065a2da90 ffff880063ecf6c0 ffffffff00000001
Call Trace:
[< inline >] udp_csum_pull_header ./include/net/udp.h:166
[<ffffffff83354ced>] udpv6_queue_rcv_skb+0x37d/0x17b0 net/ipv6/udp.c:625
[< inline >] sk_backlog_rcv ./include/net/sock.h:874
[<ffffffff82b7eec6>] __release_sock+0x126/0x3a0 net/core/sock.c:2046
[<ffffffff82b7f199>] release_sock+0x59/0x1c0 net/core/sock.c:2504
[<ffffffff8334fc50>] udpv6_sendmsg+0x1310/0x24a0 net/ipv6/udp.c:1273
[<ffffffff83174fa7>] inet_sendmsg+0x317/0x4e0 net/ipv4/af_inet.c:734
[< inline >] sock_sendmsg_nosec net/socket.c:621
[<ffffffff82b7176c>] sock_sendmsg+0xcc/0x110 net/socket.c:631
[<ffffffff82b719d1>] sock_write_iter+0x221/0x3b0 net/socket.c:829
[<ffffffff8151e69b>] do_iter_readv_writev+0x2bb/0x3f0 fs/read_write.c:695
[<ffffffff81520501>] do_readv_writev+0x431/0x730 fs/read_write.c:872
[<ffffffff81520d2f>] vfs_writev+0x8f/0xc0 fs/read_write.c:911
[<ffffffff81520e41>] do_writev+0xe1/0x240 fs/read_write.c:944
[< inline >] SYSC_writev fs/read_write.c:1017
[<ffffffff81523ca7>] SyS_writev+0x27/0x30 fs/read_write.c:1014
[<ffffffff83fc4381>] entry_SYSCALL_64_fastpath+0x1f/0xc2
arch/x86/entry/entry_64.S:209
Code: 89 f8 49 c1 e8 03 47 0f b6 14 08 45 84 d2 74 0a 41 80 fa 03 0f
8e cf 00 00 00 80 a3 91 00 00 00 f9 e9 43 ff ff ff e8 3b 79 79 fe <0f>
0b e8 34 79 79 fe 0f 0b e8 2d 79 79 fe 48 8b 7d d0 31 d2 44
RIP [<ffffffff82b8fd85>] skb_pull_rcsum+0x255/0x350 net/core/skbuff.c:3029
RSP <ffff880063ecf660>
---[ end trace a5d5d2cef6a25ecb ]---
==================================================================
// autogenerated by syzkaller (http://github.com/google/syzkaller)

#ifndef __NR_mmap
#define __NR_mmap 9
#endif
#ifndef __NR_bind
#define __NR_bind 49
#endif
#ifndef __NR_sendmsg
#define __NR_sendmsg 46
#endif
#ifndef __NR_writev
#define __NR_writev 20
#endif
#ifndef __NR_socket
#define __NR_socket 41
#endif
#ifndef __NR_syz_fuse_mount
#define __NR_syz_fuse_mount 1000004
#endif
#ifndef __NR_syz_fuseblk_mount
#define __NR_syz_fuseblk_mount 1000005
#endif
#ifndef __NR_syz_open_dev
#define __NR_syz_open_dev 1000002
#endif
#ifndef __NR_syz_open_pts
#define __NR_syz_open_pts 1000003
#endif
#ifndef __NR_syz_test
#define __NR_syz_test 1000001
#endif

#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <net/if_arp.h>

#include <errno.h>
#include <error.h>
#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 <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[17];

int main()
{
install_segv_handler();
memset(r, -1, sizeof(r));
r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0x35000ul, 0x3ul,
0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
r[1] = execute_syscall(__NR_socket, 0xaul, 0x2ul, 0x88ul, 0, 0, 0, 0,
0, 0);
NONFAILING(memcpy(
(void*)0x20034000,
"\x0a\x00\x42\x42\x7a\x85\x86\xb4\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\x00\x00\x00\x01\xb4\x73\x17\x84\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[3] = execute_syscall(__NR_bind, r[1], 0x20034000ul, 0x80ul, 0, 0, 0,
0, 0, 0);
NONFAILING(*(uint64_t*)0x2002b000 = (uint64_t)0x20021f80);
NONFAILING(*(uint32_t*)0x2002b008 = (uint32_t)0x80);
NONFAILING(*(uint64_t*)0x2002b010 = (uint64_t)0x2001f000);
NONFAILING(*(uint64_t*)0x2002b018 = (uint64_t)0x0);
NONFAILING(*(uint64_t*)0x2002b020 = (uint64_t)0x20027000);
NONFAILING(*(uint64_t*)0x2002b028 = (uint64_t)0x0);
NONFAILING(*(uint32_t*)0x2002b030 = (uint32_t)0x0);
NONFAILING(memcpy(
(void*)0x20021f80,
"\x0a\x00\x42\x42\xbe\xf9\xa8\xa3\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\x00\x00\x00\x01\x7f\xdb\x0d\xf1\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[12] = execute_syscall(__NR_sendmsg, r[1], 0x2002b000ul, 0x8000ul, 0,
0, 0, 0, 0, 0);
NONFAILING(*(uint64_t*)0x20032fe0 = (uint64_t)0x20032000);
NONFAILING(*(uint64_t*)0x20032fe8 = (uint64_t)0x1);
NONFAILING(memcpy((void*)0x20032000, "\x0d", 1));
r[16] = execute_syscall(__NR_writev, r[1], 0x20032fe0ul, 0x1ul, 0, 0,
0, 0, 0, 0);
return 0;
}

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Next in thread: Eric Dumazet: "Re: net/udp: bug in skb_pull_rcsum"
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