[+Cc tglx@xxxxxxxxxxxxx ] On Sat, Dec 02, 2017 at 09:10:01PM -0800, syzbot wrote: > syzkaller has found reproducer for the following crash on > 2db767d9889cef087149a5eaa35c1497671fa40f > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master > compiler: gcc (GCC) 7.1.1 20170620 > .config is attached > Raw console output is attached. > C reproducer is attached > syzkaller reproducer is attached. See https://goo.gl/kgGztJ > for information about syzkaller reproducers > > > 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 > Dumping ftrace buffer: > (ftrace buffer empty) > Modules linked in: > CPU: 0 PID: 3075 Comm: syzkaller531375 Not tainted 4.15.0-rc1+ #205 > Hardware name: Google Google Compute Engine/Google Compute Engine, > BIOS Google 01/01/2011 > task: 00000000523f1e90 task.stack: 00000000c2d38485 > RIP: 0010:string+0xb4/0x200 lib/vsprintf.c:595 > RSP: 0018:ffff8801cc637868 EFLAGS: 00010006 > RAX: dffffc0000000000 RBX: fffffffffffffffe RCX: ffffffff85135fbf > RDX: 06c7240eabebe406 RSI: 1ffff100398c6f01 RDI: ffff8801cc637888 > RBP: ffff8801cc6378b8 R08: ffffed00398a5566 R09: ffffed00398a5566 > R10: 0000000000000002 R11: ffffed00398a5565 R12: 363920755f5f2034 > R13: 363920755f5f2033 R14: ffffffffffffffff R15: ffff8801cc52ab2a > FS: 0000000001a75880(0000) GS:ffff8801db400000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00000000205e2ff0 CR3: 00000001cc470000 CR4: 00000000001406f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > vsnprintf+0x863/0x1900 lib/vsprintf.c:2282 > seq_vprintf+0xe3/0x1a0 fs/seq_file.c:397 > seq_printf+0xb3/0xe0 fs/seq_file.c:412 > show_timer+0x1ee/0x2b0 fs/proc/base.c:2274 > seq_read+0x385/0x13d0 fs/seq_file.c:234 > do_loop_readv_writev fs/read_write.c:673 [inline] > do_iter_read+0x3db/0x5b0 fs/read_write.c:897 > vfs_readv+0x121/0x1c0 fs/read_write.c:959 > do_preadv+0x11b/0x1a0 fs/read_write.c:1043 > SYSC_preadv fs/read_write.c:1093 [inline] > SyS_preadv+0x30/0x40 fs/read_write.c:1088 > entry_SYSCALL_64_fastpath+0x1f/0x96 > RIP: 0033:0x440149 > RSP: 002b:00007fff96d72b08 EFLAGS: 00000213 ORIG_RAX: 0000000000000127 > RAX: ffffffffffffffda RBX: 00007fff96d72b10 RCX: 0000000000440149 > RDX: 0000000000000001 RSI: 00000000205e2ff0 RDI: 0000000000000003 > RBP: 0000000000000000 R08: 0000000000000011 R09: 65732f636f72702f > R10: 0000000000000000 R11: 0000000000000213 R12: 0000000000401a10 > R13: 0000000000401aa0 R14: 0000000000000000 R15: 0000000000000000 > Code: 01 00 00 e8 7f 98 5c fc 4d 85 f6 0f 84 10 01 00 00 e8 71 98 5c > fc 4c 89 ea 48 b8 00 00 00 00 00 fc ff df 4d 8d 65 01 48 c1 ea 03 > <0f> b6 04 02 4c 89 ea 83 e2 07 38 d0 7f 08 84 c0 0f 85 ec 00 00 > RIP: string+0xb4/0x200 lib/vsprintf.c:595 RSP: ffff8801cc637868 > ---[ end trace 3570c98033660e3f ]--- The bug is that sys_timer_create() allows setting ->it_sigev_notify to almost any value, but show_timer() assumes that it has one of a specific set of values. Here's a simplified reproducer: #include <fcntl.h> #include <signal.h> #include <time.h> #include <unistd.h> int main() { struct sigevent e = { .sigev_signo = 0x1c, .sigev_notify = 0x100000, }; timer_t t; int fd; char buf[64]; timer_create(CLOCK_MONOTONIC, &e, &t); fd = open("/proc/self/timers", O_RDONLY); read(fd, buf, sizeof(buf)); } I wonder if anything would break if we made sys_timer_create() return -EINVAL for unrecognized values of sigev_notify? That's what it *should* do, but it seems to be the classic "unchecked flags" bug, yet again... Eric
