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SubjectUBSAN: Undefined error in time.h signed integer overflow
Hi,

I encountered this bug while fuzzing linux kernel 4.13-rc7 with syzkaller.

================================================================================
UBSAN: Undefined behaviour in ./include/linux/time.h:233:27
signed integer overflow:
8391720337152500783 * 1000000000 cannot be represented in type 'long int'
CPU: 0 PID: 31798 Comm: syz-executor2 Not tainted 4.13.0-rc7 #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
Ubuntu-1.8.2-1ubuntu1 04/01/2014
Call Trace:
__dump_stack lib/dump_stack.c:16 [inline]
dump_stack+0xf7/0x1ae lib/dump_stack.c:52
ubsan_epilogue+0x12/0x8f lib/ubsan.c:164
handle_overflow+0x21e/0x292 lib/ubsan.c:195
__ubsan_handle_mul_overflow+0x2a/0x3e lib/ubsan.c:219
timespec_to_ns include/linux/time.h:233 [inline]
posix_cpu_timer_set+0xb5c/0xf20 kernel/time/posix-cpu-timers.c:686
do_timer_settime+0x1f4/0x390 kernel/time/posix-timers.c:890
SYSC_timer_settime kernel/time/posix-timers.c:916 [inline]
SyS_timer_settime+0xea/0x170 kernel/time/posix-timers.c:902
entry_SYSCALL_64_fastpath+0x18/0xad
RIP: 0033:0x451e59
RSP: 002b:00007fb62af4fc08 EFLAGS: 00000216 ORIG_RAX: 00000000000000df
RAX: ffffffffffffffda RBX: 0000000000718000 RCX: 0000000000451e59
RDX: 0000000020006000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000046 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020003fe0 R11: 0000000000000216 R12: 00000000004be920
R13: 00000000ffffffff R14: ffffffffffffffff R15: 0000000000000000
================================================================================


Here is the full reproducer program: https://pastebin.com/xucAtmbD

Below is the core of the reproducer:

long r[16];
void *thr(void *arg)
{
switch ((long)arg) {
case 0:
r[0] = syscall(__NR_mmap, 0x20000000ul, 0xd000ul, 0x3ul, 0x32ul,
0xfffffffffffffffful, 0x0ul);
break;
case 1:
NONFAILING(*(uint64_t*)0x20001fb0 = (uint64_t)0x0);
NONFAILING(*(uint32_t*)0x20001fb8 = (uint32_t)0x1);
NONFAILING(*(uint32_t*)0x20001fbc = (uint32_t)0x0);
NONFAILING(*(uint64_t*)0x20001fc0 = (uint64_t)0x20007fcd);
NONFAILING(*(uint64_t*)0x20001fc8 = (uint64_t)0x20005000);
r[6] = syscall(__NR_timer_create, 0x3ul, 0x20001fb0ul, 0x20000000ul);
break;
case 2:
r[7] = syscall(__NR_clock_gettime, 0x0ul, 0x20004000ul);
if (r[7] != -1)
NONFAILING(r[8] = *(uint64_t*)0x20004008);
break;
case 3:
NONFAILING(*(uint64_t*)0x20006000 = (uint64_t)0x0);
NONFAILING(*(uint64_t*)0x20006008 = (uint64_t)0x0);
NONFAILING(*(uint64_t*)0x20006010 = (uint64_t)0x0);
NONFAILING(*(uint64_t*)0x20006018 = r[8]+10000000);
r[13] = syscall(__NR_timer_settime, 0x0ul, 0x0ul, 0x20006000ul, 0x20003fe0ul);
break;
case 4:
NONFAILING(memcpy((void*)0x20006000,
"\x2f\x64\x65\x76\x2f\x61\x75\x74\x6f\x66\x73\x00", 12));
r[15] = syscall(__NR_openat, 0xffffffffffffff9cul, 0x20006000ul,
0x8000ul, 0x0ul);
break;
}
return 0;
}

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