WARNING in __mark_chain_precision

WARNING in __mark_chain_precision

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    e5a3e259 Merge branch 'bpf-tcp-rtt-hook'
git tree:       bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14190c2da00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dd16b8dc9d0d210c
dashboard link: https://syzkaller.appspot.com/bug?extid=4da3ff23081bafe74fc2
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1409ce0da00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17226a0da00000

The bug was bisected to:

commit b53119f13a04879c3bf502828d99d13726639ead
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu Mar 7 01:22:54 2019 +0000

     pin iocb through aio.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11427b8ba00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=13427b8ba00000
console output: https://syzkaller.appspot.com/x/log.txt?x=15427b8ba00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4da3ff23081bafe74fc2@syzkaller.appspotmail.com
Fixes: b53119f13a04 ("pin iocb through aio.")

------------[ cut here ]------------
verifier backtracking bug
WARNING: CPU: 0 PID: 9104 at kernel/bpf/verifier.c:1785  
__mark_chain_precision+0x19bb/0x1ee0 kernel/bpf/verifier.c:1785
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 9104 Comm: syz-executor284 Not tainted 5.2.0-rc5+ #34
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+0x172/0x1f0 lib/dump_stack.c:113
  panic+0x2cb/0x744 kernel/panic.c:219
  __warn.cold+0x20/0x4d kernel/panic.c:576
  report_bug+0x263/0x2b0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:179 [inline]
  fixup_bug arch/x86/kernel/traps.c:174 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:986
RIP: 0010:__mark_chain_precision+0x19bb/0x1ee0 kernel/bpf/verifier.c:1785
Code: 08 31 ff 89 de e8 95 ba f2 ff 84 db 0f 85 ce fe ff ff e8 48 b9 f2 ff  
48 c7 c7 e0 44 91 87 c6 05 1c 15 1f 08 01 e8 03 f1 c4 ff <0f> 0b 41 bc f2  
ff ff ff e9 af fe ff ff e8 d3 3c 2c 00 e9 c2 e7 ff
RSP: 0018:ffff88809f04f380 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815ad926 RDI: ffffed1013e09e62
RBP: ffff88809f04f4d0 R08: ffff88809987a540 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff88809af0c280 R14: 0000000000000001 R15: ffff88809f65cb00
  mark_chain_precision kernel/bpf/verifier.c:1822 [inline]
  check_cond_jmp_op+0xcd8/0x3c30 kernel/bpf/verifier.c:5842
  do_check+0x60f4/0x8a20 kernel/bpf/verifier.c:7782
  bpf_check+0x6f99/0x9950 kernel/bpf/verifier.c:9293
  bpf_prog_load+0xe68/0x1670 kernel/bpf/syscall.c:1698
  __do_sys_bpf+0xa20/0x42d0 kernel/bpf/syscall.c:2849
  __se_sys_bpf kernel/bpf/syscall.c:2808 [inline]
  __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:2808
  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440369
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffca85a2fa8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440369
RDX: 0000000000000048 RSI: 0000000020000200 RDI: 0000000000000005
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000246 R12: 0000000000401bf0
R13: 0000000000401c80 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

Re: WARNING in __mark_chain_precision

[Andrii Nakryiko]

#syz test: https://github.com/anakryiko/linux bpf-fix-precise-bpf_st

Re: WARNING in __mark_chain_precision

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger  
crash:

Reported-and-tested-by:  
syzbot+4da3ff23081bafe74fc2@syzkaller.appspotmail.com

Tested on:

commit:         b9321614 bpf: fix precision bit propagation for BPF_ST ins..
git tree:       https://github.com/anakryiko/linux bpf-fix-precise-bpf_st
kernel config:  https://syzkaller.appspot.com/x/.config?x=6bb3e6e7997c14f9
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Note: testing is done by a robot and is best-effort only.