[syzbot] [bpf?] UBSAN: array-index-out-of-bounds in print_bpf_insn

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f7e6bd33d1d4 Merge branch 'bpf-support-new-insns-from-cpu-..
git tree: bpf-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=114d3019a80000
kernel config: https://syzkaller.appspot.com/x/.config?x=8acaeb93ad7c6aaa
dashboard link: https://syzkaller.appspot.com/bug?extid=3758842a6c01012aa73b
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=15165dbea80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12259911a80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f17904bb7ff9/disk-f7e6bd33.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8d3ac62bba3c/vmlinux-f7e6bd33.xz
kernel image: https://storage.googleapis.com/syzbot-assets/62e7226b925f/bzImage-f7e6bd33.xz

The issue was bisected to:

commit f835bb6222998c8655bc4e85287d42b57c17b208
Author: Yonghong Song <yongho...@linux.dev>
Date: Wed Jun 28 22:29:51 2023 +0000

bpf: Add kernel/bpftool asm support for new instructions

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=11fe5779a80000
final oops: https://syzkaller.appspot.com/x/report.txt?x=13fe5779a80000
console output: https://syzkaller.appspot.com/x/log.txt?x=15fe5779a80000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+375884...@syzkaller.appspotmail.com
Fixes: f835bb622299 ("bpf: Add kernel/bpftool asm support for new instructions")

================================================================================
UBSAN: array-index-out-of-bounds in kernel/bpf/disasm.c:192:38
index -1 is out of range for type 'char *[4]'
CPU: 1 PID: 5026 Comm: syz-executor300 Not tainted 6.5.0-rc2-syzkaller-00599-gf7e6bd33d1d4 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x125/0x1b0 lib/dump_stack.c:106
ubsan_epilogue lib/ubsan.c:217 [inline]
__ubsan_handle_out_of_bounds+0x111/0x150 lib/ubsan.c:348
print_bpf_insn+0x22d9/0x23c0 kernel/bpf/disasm.c:192
do_check kernel/bpf/verifier.c:16505 [inline]
do_check_common+0x1402/0xd370 kernel/bpf/verifier.c:19061
do_check_main kernel/bpf/verifier.c:19124 [inline]
bpf_check+0x8436/0xac50 kernel/bpf/verifier.c:19748
bpf_prog_load+0x153a/0x2270 kernel/bpf/syscall.c:2709
__sys_bpf+0xeed/0x4ec0 kernel/bpf/syscall.c:5345
__do_sys_bpf kernel/bpf/syscall.c:5449 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5447 [inline]
__x64_sys_bpf+0x78/0xc0 kernel/bpf/syscall.c:5447
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f6f30a1b3a9
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:00007ffee3c35308 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007ffee3c354e8 RCX: 00007f6f30a1b3a9
RDX: 0000000000000048 RSI: 0000000020000080 RDI: 0000000000000005
RBP: 00007f6f30a8e610 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffee3c354d8 R14: 0000000000000001 R15: 0000000000000001
</TASK>
================================================================================


---
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[syzbot]

Hello,

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

Reported-and-tested-by: syzbot+375884...@syzkaller.appspotmail.com

Tested on:

commit: fdf0eaf1 Linux 6.5-rc2
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git v6.5-rc2
console output: https://syzkaller.appspot.com/x/log.txt?x=1223978da80000
kernel config: https://syzkaller.appspot.com/x/.config?x=77b9a3cf8f44c6da

dashboard link: https://syzkaller.appspot.com/bug?extid=3758842a6c01012aa73b
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.