WARNING in bpf_check (2)

WARNING in bpf_check (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    ccda4af0f4b9 Linux 4.20-rc2
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=129edfbd400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4a0a89f12ca9b0f5
dashboard link: https://syzkaller.appspot.com/bug?extid=4fc427c7af994b0948be
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=172b626d400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=148dcb0b400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4fc427c7af994b0948be@syzkaller.appspotmail.com

audit: type=1400 audit(1542221670.986:36): avc:  denied  { map } for   
pid=6270 comm="syz-executor244" path="/root/syz-executor244665442"  
dev="sda1" ino=16484 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023  
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
------------[ cut here ]------------
audit: type=1400 audit(1542221670.986:37): avc:  denied  { prog_load } for   
pid=6270 comm="syz-executor244"  
scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023  
tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=bpf  
permissive=1
verifier bug. No program starts at insn 7
WARNING: CPU: 0 PID: 6270 at kernel/bpf/verifier.c:5880 jit_subprogs  
kernel/bpf/verifier.c:5879 [inline]
WARNING: CPU: 0 PID: 6270 at kernel/bpf/verifier.c:5880 fixup_call_args  
kernel/bpf/verifier.c:6023 [inline]
WARNING: CPU: 0 PID: 6270 at kernel/bpf/verifier.c:5880  
bpf_check+0x5461/0x6310 kernel/bpf/verifier.c:6404
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 6270 Comm: syz-executor244 Not tainted 4.20.0-rc2+ #112
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+0x244/0x39d lib/dump_stack.c:113
  panic+0x2ad/0x55c kernel/panic.c:188
  __warn.cold.8+0x20/0x45 kernel/panic.c:540
  report_bug+0x254/0x2d0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:178 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
  do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
RIP: 0010:jit_subprogs kernel/bpf/verifier.c:5879 [inline]
RIP: 0010:fixup_call_args kernel/bpf/verifier.c:6023 [inline]
RIP: 0010:bpf_check+0x5461/0x6310 kernel/bpf/verifier.c:6404
Code: b6 14 02 4c 89 f0 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 69 0b 00  
00 8b 73 04 48 c7 c7 c0 ca 30 88 44 01 ee e8 4f 14 b9 ff <0f> 0b 48 8b 54  
24 08 b8 ff ff 37 00 48 c1 e0 2a 48 c1 ea 03 0f b6
RSP: 0018:ffff8881c126f980 EFLAGS: 00010286
RAX: 0000000000000000 RBX: ffffc90005e13040 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8165e7e5 RDI: 0000000000000005
RBP: ffff8881c126fb30 R08: ffff8881a322e0c0 R09: ffffed103b5c5020
R10: ffffed103b5c5020 R11: ffff8881dae28107 R12: 0000000000000000
R13: 0000000000000002 R14: ffffc90005e13044 R15: ffff8881c0da6380
  bpf_prog_load+0x113d/0x1cc0 kernel/bpf/syscall.c:1528
  __do_sys_bpf kernel/bpf/syscall.c:2504 [inline]
  __se_sys_bpf kernel/bpf/syscall.c:2466 [inline]
  __x64_sys_bpf+0x36c/0x520 kernel/bpf/syscall.c:2466
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440159
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:00007fff04546138 EFLAGS: 00000207 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440159
RDX: 0000000000000048 RSI: 0000000020000000 RDI: 0000000000000005
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000207 R12: 00000000004019e0
R13: 0000000000401a70 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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Re: WARNING in bpf_check (2)

[Edward Cree]

On 15/11/18 07:49, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    ccda4af0f4b9 Linux 4.20-rc2
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=129edfbd400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4a0a89f12ca9b0f5
> dashboard link: https://syzkaller.appspot.com/bug?extid=4fc427c7af994b0948be
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=172b626d400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=148dcb0b400000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+4fc427c7af994b0948be@syzkaller.appspotmail.com
I'm investigating this.  So far I have disassembled the prog and reproduced
 the failure by adding the following to test_verifier.c:
    {
        "syz found: explosion",
        .insns = {
            BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
            BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 1, 0, 5),
            BPF_JMP_REG(BPF_JSGT, BPF_REG_0, BPF_REG_0, 0),
            BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
            BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 1, 0, 2),
            BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
            BPF_EXIT_INSN(),
            BPF_LDX_MEM(BPF_B, BPF_REG_9, BPF_REG_1, 0),
            BPF_MOV64_IMM(BPF_REG_0, 0),
            BPF_EXIT_INSN(),
        },
        .prog_type = BPF_PROG_TYPE_SOCKET_FILTER,
        .result = ACCEPT,
    },
A subprog _does_ start at insn 7, and the verifier was happy with it until
 jit_subprogs, suggesting that something has mangled env->subprog_info[].start
 or else insns have been inserted but the call insns not adjusted.
The obvious suspect would be adjust_subprog_starts() and/or
 bpf_patch_insn_data().

-Ed