Re: [syzbot] [bpf?] KMSAN: uninit-value in percpu_array_map_lookup_percpu_elem

[Martin KaFai Lau]

On 4/2/24 10:22 AM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    39cd87c4eb2b Linux 6.9-rc2
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=13891cc5180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5112b3f484393436
> dashboard link: https://syzkaller.appspot.com/bug?extid=aca389a8a7da35c070ce
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11629a19180000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=169e86e5180000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/dba7eac545d2/disk-39cd87c4.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/ddf1c8e07b17/vmlinux-39cd87c4.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/808527761eab/bzImage-39cd87c4.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+aca389a8a7da35c070ce@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> =====================================================
> BUG: KMSAN: uninit-value in percpu_array_map_lookup_percpu_elem+0x1cb/0x200 kernel/bpf/arraymap.c:257
>   percpu_array_map_lookup_percpu_elem+0x1cb/0x200 kernel/bpf/arraymap.c:257
>   ____bpf_map_lookup_percpu_elem kernel/bpf/helpers.c:133 [inline]
>   bpf_map_lookup_percpu_elem+0x67/0x90 kernel/bpf/helpers.c:130
>   ___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997
>   __bpf_prog_run288+0xb5/0xe0 kernel/bpf/core.c:2237
>   bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
>   __bpf_prog_run include/linux/filter.h:657 [inline]
>   bpf_prog_run include/linux/filter.h:664 [inline]
>   __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
>   bpf_trace_run8+0x1bd/0x3a0 kernel/trace/bpf_trace.c:2426
>   __bpf_trace_jbd2_handle_stats+0x51/0x70 include/trace/events/jbd2.h:210
>   trace_jbd2_handle_stats include/trace/events/jbd2.h:210 [inline]
>   jbd2_journal_stop+0x1157/0x12c0 fs/jbd2/transaction.c:1869
>   __ext4_journal_stop+0x115/0x310 fs/ext4/ext4_jbd2.c:134
>   ext4_do_writepages+0x1c3c/0x62e0 fs/ext4/inode.c:2692
>   ext4_writepages+0x312/0x830 fs/ext4/inode.c:2768
>   do_writepages+0x427/0xc30 mm/page-writeback.c:2612
>   __writeback_single_inode+0x10d/0x12c0 fs/fs-writeback.c:1650
>   writeback_sb_inodes+0xb48/0x1be0 fs/fs-writeback.c:1941
>   __writeback_inodes_wb+0x14c/0x440 fs/fs-writeback.c:2012
>   wb_writeback+0x4da/0xdf0 fs/fs-writeback.c:2119
>   wb_check_old_data_flush fs/fs-writeback.c:2223 [inline]
>   wb_do_writeback fs/fs-writeback.c:2276 [inline]
>   wb_workfn+0x110c/0x1940 fs/fs-writeback.c:2304
>   process_one_work kernel/workqueue.c:3254 [inline]
>   process_scheduled_works+0xa81/0x1bd0 kernel/workqueue.c:3335
>   worker_thread+0xea5/0x1560 kernel/workqueue.c:3416
>   kthread+0x3e2/0x540 kernel/kthread.c:388
>   ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:147
>   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
>
> Local variable stack created at:
>   __bpf_prog_run288+0x45/0xe0 kernel/bpf/core.c:2237
>   bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
>   __bpf_prog_run include/linux/filter.h:657 [inline]
>   bpf_prog_run include/linux/filter.h:664 [inline]
>   __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
>   bpf_trace_run8+0x1bd/0x3a0 kernel/trace/bpf_trace.c:2426
>
> CPU: 1 PID: 1070 Comm: kworker/u8:7 Not tainted 6.9.0-rc2-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> Workqueue: writeback wb_workfn (flush-8:0)
> =====================================================

#syz dup: [syzbot] [bpf?] [net?] KMSAN: uninit-value in dev_map_lookup_elem