Re: [syzbot] [bpf?] general protection fault in btf_is_module

From: Martin KaFai Lau
Date: Thu Jan 25 2024 - 13:02:37 EST

On 1/25/24 1:50 AM, syzbot wrote:
Hello,

syzbot found the following issue on:

HEAD commit: d47b9f68d289 libbpf: Correct bpf_core_read.h comment wrt b..
git tree: bpf-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=104b1ef7e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=719e6acaf392d56b
dashboard link: https://syzkaller.appspot.com/bug?extid=1336f3d4b10bcda75b89
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10c1a53be80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1052cec3e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1a9b4a5622fb/disk-d47b9f68.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dd68baeac4fd/vmlinux-d47b9f68.xz
kernel image: https://storage.googleapis.com/syzbot-assets/811ba9dc9ddf/bzImage-d47b9f68.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1336f3d4b10bcda75b89@xxxxxxxxxxxxxxxxxxxxxxxxx

general protection fault, probably for non-canonical address 0xdffffc000000001b: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x00000000000000d8-0x00000000000000df]
CPU: 0 PID: 5064 Comm: syz-executor334 Not tainted 6.7.0-syzkaller-12348-gd47b9f68d289 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
RIP: 0010:btf_is_module+0x26/0x80 kernel/bpf/btf.c:7441
Code: 00 eb f0 90 66 0f 1f 00 55 53 48 89 fb e8 92 24 de ff 48 8d bb d8 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 02 7e 48 0f b6 ab d8 00 00 00 31 ff 89 ee e8
RSP: 0018:ffffc900039ff828 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81a07f47
RDX: 000000000000001b RSI: ffffffff81a9fcfe RDI: 00000000000000d8
RBP: ffffc900039ffaf0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000004 R11: ffffffff8aa0008b R12: ffffc90000ae6038
R13: ffffc90000ae6000 R14: 0000000000000000 R15: 0000000000000000
FS: 000055555660b380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001b6b398 CR3: 000000001aaae000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
check_struct_ops_btf_id kernel/bpf/verifier.c:20302 [inline]

Kui-Feng, it should be due to the commit e3f87fdfed7b ("bpf: hold module refcnt in bpf_struct_ops map creation and prog verification."). I think it needs a NULL check on the return value from bpf_get_btf_vmlinux().

Please take a look. Thanks.


check_attach_btf_id kernel/bpf/verifier.c:20730 [inline]
bpf_check+0x6cfe/0x9df0 kernel/bpf/verifier.c:20898
bpf_prog_load+0x14dc/0x2310 kernel/bpf/syscall.c:2769
__sys_bpf+0xbf7/0x4a00 kernel/bpf/syscall.c:5463
__do_sys_bpf kernel/bpf/syscall.c:5567 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5565 [inline]
__x64_sys_bpf+0x78/0xc0 kernel/bpf/syscall.c:5565
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xd3/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f4dbbe514a9
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe76acbe18 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007ffe76acbff8 RCX: 00007f4dbbe514a9
RDX: 00000000000000a0 RSI: 00000000200009c0 RDI: 0000000000000005
RBP: 00007f4dbbec4610 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffe76acbfe8 R14: 0000000000000001 R15: 0000000000000001
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:btf_is_module+0x26/0x80 kernel/bpf/btf.c:7441
Code: 00 eb f0 90 66 0f 1f 00 55 53 48 89 fb e8 92 24 de ff 48 8d bb d8 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 02 7e 48 0f b6 ab d8 00 00 00 31 ff 89 ee e8
RSP: 0018:ffffc900039ff828 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81a07f47
RDX: 000000000000001b RSI: ffffffff81a9fcfe RDI: 00000000000000d8
RBP: ffffc900039ffaf0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000004 R11: ffffffff8aa0008b R12: ffffc90000ae6038
R13: ffffc90000ae6000 R14: 0000000000000000 R15: 0000000000000000
FS: 000055555660b380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000001b6b398 CR3: 000000001aaae000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 00 eb add %ch,%bl
2: f0 90 lock nop
4: 66 0f 1f 00 nopw (%rax)
8: 55 push %rbp
9: 53 push %rbx
a: 48 89 fb mov %rdi,%rbx
d: e8 92 24 de ff call 0xffde24a4
12: 48 8d bb d8 00 00 00 lea 0xd8(%rbx),%rdi
19: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
20: fc ff df
23: 48 89 fa mov %rdi,%rdx
26: 48 c1 ea 03 shr $0x3,%rdx
* 2a: 0f b6 04 02 movzbl (%rdx,%rax,1),%eax <-- trapping instruction
2e: 84 c0 test %al,%al
30: 74 02 je 0x34
32: 7e 48 jle 0x7c
34: 0f b6 ab d8 00 00 00 movzbl 0xd8(%rbx),%ebp
3b: 31 ff xor %edi,%edi
3d: 89 ee mov %ebp,%esi
3f: e8 .byte 0xe8


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