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Subjectsound: division by 0 in snd_hrtimer_callback
Hello,

The following program triggers divide error in snd_hrtimer_callback:

divide error: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 3 PID: 17469 Comm: syz-executor Not tainted 4.8.0-rc3+ #33
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88003dc4a640 task.stack: ffff88003c690000
RIP: 0010:[<ffffffff8575b49c>]
[< inline >] ktime_divns ./include/linux/ktime.h:195
[<ffffffff8575b49c>] snd_hrtimer_callback+0x1bc/0x3c0 sound/core/hrtimer.c:62
RSP: 0018:ffff88006d507d98 EFLAGS: 00010006
RAX: 0000000000005f28 RBX: ffff88006c4acb48 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff88006c4acb60 RDI: ffffffff884b7a68
RBP: ffff88006d507df0 R08: 000000687d030efd R09: ffff88007fff70c8
R10: ffff88007fff70d8 R11: ffff88007fff70d0 R12: ffff88003cda70c0
R13: ffff88003cda7174 R14: ffff88003cda71f0 R15: ffff88006c4acb40
FS: 00007f131f945700(0000) GS:ffff88006d500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000451ed0 CR3: 000000005bb88000 CR4: 00000000000006e0
Stack:
0000000000000000 ffff88006c4acb60 ffff88003cda7178 0000000000005f28
ffff88006c4acba0 0000000000000000 ffff88006c4acb48 0000000000000003
ffff88006d51b400 dffffc0000000000 dffffc0000000000 ffff88006d507ee8
Call Trace:
<IRQ>
[< inline >] __run_hrtimer kernel/time/hrtimer.c:1238
[<ffffffff814f48b5>] __hrtimer_run_queues+0x325/0xe70
kernel/time/hrtimer.c:1302
[<ffffffff814f726b>] hrtimer_interrupt+0x18b/0x420 kernel/time/hrtimer.c:1336
[<ffffffff81268f8f>] local_apic_timer_interrupt+0x6f/0xe0
arch/x86/kernel/apic/apic.c:933
[<ffffffff86c27d96>] smp_apic_timer_interrupt+0x76/0xa0
arch/x86/kernel/apic/apic.c:957
[<ffffffff86c26e4c>] apic_timer_interrupt+0x8c/0xa0
arch/x86/entry/entry_64.S:455
<EOI>
[< inline >] spin_unlock_irqrestore ./include/linux/spinlock.h:362
[<ffffffff85750f7d>] snd_timer_start1+0xdd/0x590 sound/core/timer.c:464
[<ffffffff857532b5>] snd_timer_continue+0x45/0x80 sound/core/timer.c:593
[< inline >] snd_timer_user_continue sound/core/timer.c:1821
[< inline >] __snd_timer_user_ioctl sound/core/timer.c:1888
[<ffffffff85758ce9>] snd_timer_user_ioctl+0xe99/0x2470 sound/core/timer.c:1903
[< inline >] vfs_ioctl fs/ioctl.c:43
[<ffffffff8186f1fc>] do_vfs_ioctl+0x18c/0x1080 fs/ioctl.c:675
[< inline >] SYSC_ioctl fs/ioctl.c:690
[<ffffffff8187017f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:681
[<ffffffff86c25480>] entry_SYSCALL_64_fastpath+0x23/0xc1
arch/x86/entry/entry_64.S:207
Code: 6b 45 e5 fb 8b 0d e5 ca 64 05 48 0f af 4d d0 48 85 c9 0f 88 6a
01 00 00 48 89 4d a8 e8 4e 45 e5 fb 48 8b 45 c0 48 8b 4d a8 48 99 <48>
f7 f9 48 01 45 d0 e8 38 45 e5 fb 4c 89 fa 48 b8 00 00 00 00
RIP [< inline >] ktime_divns ./include/linux/ktime.h:195
RIP [<ffffffff8575b49c>] snd_hrtimer_callback+0x1bc/0x3c0
sound/core/hrtimer.c:62
RSP <ffff88006d507d98>
---[ end trace b12f88d370b1ccee ]---
Kernel panic - not syncing: Fatal exception in interrupt


On commit 61c04572de404e52a655a36752e696bbcb483cf5 (Aug 25).



// autogenerated by syzkaller (http://github.com/google/syzkaller)
#ifndef __NR_mmap
#define __NR_mmap 9
#endif
#ifndef __NR_syz_open_dev
#define __NR_syz_open_dev 1000001
#endif
#ifndef __NR_ioctl
#define __NR_ioctl 16
#endif
#ifndef __NR_syz_fuse_mount
#define __NR_syz_fuse_mount 1000003
#endif
#ifndef __NR_syz_fuseblk_mount
#define __NR_syz_fuseblk_mount 1000004
#endif
#ifndef __NR_syz_open_pts
#define __NR_syz_open_pts 1000002
#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_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[42];

int main()
{
install_segv_handler();
memset(r, -1, sizeof(r));
r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0xd000ul, 0x3ul,
0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
NONFAILING(memcpy(
(void*)0x20003000,
"\x2f\x64\x65\x76\x2f\x73\x6e\x64\x2f\x74\x69\x6d\x65\x72\x00",
15));
r[2] = execute_syscall(__NR_syz_open_dev, 0x20003000ul, 0x0ul, 0x1ul,
0, 0, 0, 0, 0, 0);
NONFAILING(*(uint32_t*)0x2000bfcc = (uint32_t)0x1);
NONFAILING(*(uint32_t*)0x2000bfd0 = (uint32_t)0x4);
NONFAILING(*(uint32_t*)0x2000bfd4 = (uint32_t)0x2);
NONFAILING(*(uint32_t*)0x2000bfd8 = (uint32_t)0x3);
NONFAILING(*(uint32_t*)0x2000bfdc = (uint32_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe0 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe1 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe2 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe3 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe4 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe5 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe6 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe7 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe8 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfe9 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfea = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfeb = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfec = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfed = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfee = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfef = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff0 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff1 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff2 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff3 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff4 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff5 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff6 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff7 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff8 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bff9 = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bffa = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bffb = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bffc = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bffd = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bffe = (uint8_t)0x0);
NONFAILING(*(uint8_t*)0x2000bfff = (uint8_t)0x0);
r[40] = execute_syscall(__NR_ioctl, r[2], 0x40345410ul, 0x2000bfccul,
0, 0, 0, 0, 0, 0);
r[41] =
execute_syscall(__NR_ioctl, r[2], 0x54a2ul, 0, 0, 0, 0, 0, 0, 0);
return 0;
}

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