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; }