KASAN: use-after-free Write in process_preds

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    03f5781be2c7 bpf, x86_32: add eBPF JIT compiler for ia32
git tree:       bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13627237800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3d356c2d908b7293
dashboard link: https://syzkaller.appspot.com/bug?extid=873ae613c636f037d5f8
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+873ae613c636f037d5f8@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in predicate_parse  
kernel/trace/trace_events_filter.c:557 [inline]
BUG: KASAN: use-after-free in process_preds+0x1958/0x19b0  
kernel/trace/trace_events_filter.c:1505
Write of size 4 at addr ffff8801ada34ff0 by task syz-executor3/6458

CPU: 0 PID: 6458 Comm: syz-executor3 Not tainted 4.17.0-rc2+ #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 print_address_description+0x6c/0x20b mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
 __asan_report_store4_noabort+0x17/0x20 mm/kasan/report.c:437
 predicate_parse kernel/trace/trace_events_filter.c:557 [inline]
 process_preds+0x1958/0x19b0 kernel/trace/trace_events_filter.c:1505
 create_filter+0x155/0x270 kernel/trace/trace_events_filter.c:1713
 ftrace_profile_set_filter+0x130/0x2e0  
kernel/trace/trace_events_filter.c:2038
 perf_event_set_filter+0x248/0x1230 kernel/events/core.c:9079
 _perf_ioctl+0x84c/0x15e0 kernel/events/core.c:5059
 perf_ioctl+0x59/0x80 kernel/events/core.c:5110
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
 __do_sys_ioctl fs/ioctl.c:708 [inline]
 __se_sys_ioctl fs/ioctl.c:706 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455979
RSP: 002b:00007fd67f515c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd67f5166d4 RCX: 0000000000455979
RDX: 0000000020000040 RSI: 0000000040082406 RDI: 0000000000000013
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000002bf R14: 00000000006f8288 R15: 0000000000000000

The buggy address belongs to the page:
page:ffffea0006b68d00 count:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: ffff8801daf2fcd8 ffffea0006a5d9e0 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801ada34e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801ada34f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff8801ada34f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                             ^
 ffff8801ada35000: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
 ffff8801ada35080: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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