Re: [syzbot] [net?] KMSAN: uninit-value in __vxlan_find_mac

[Ido Schimmel <idosch@idosch.org>]

On Thu, Nov 14, 2024 at 02:40:26AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    de2f378f2b77 Merge tag 'nfsd-6.12-4' of git://git.kernel.o..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15b170c0580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e4580d62ee1893a5
> dashboard link: https://syzkaller.appspot.com/bug?extid=35e7e2811bbe5777b20e
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/f0ff1d637186/disk-de2f378f.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/1515128a919f/vmlinux-de2f378f.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/6624bf235bc6/bzImage-de2f378f.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+35e7e2811bbe5777b20e@syzkaller.appspotmail.com
> 
> =====================================================
> BUG: KMSAN: uninit-value in __vxlan_find_mac+0x497/0x4e0
>  __vxlan_find_mac+0x497/0x4e0
>  vxlan_find_mac drivers/net/vxlan/vxlan_core.c:436 [inline]
>  vxlan_xmit+0x1669/0x39f0 drivers/net/vxlan/vxlan_core.c:2753

Missing a check that we have enough bytes for the Ethernet header.
Will look into it.

>  __netdev_start_xmit include/linux/netdevice.h:4928 [inline]
>  netdev_start_xmit include/linux/netdevice.h:4937 [inline]
>  xmit_one net/core/dev.c:3588 [inline]
>  dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3604
>  __dev_queue_xmit+0x3562/0x56d0 net/core/dev.c:4432
>  dev_queue_xmit include/linux/netdevice.h:3094 [inline]
>  __bpf_tx_skb net/core/filter.c:2152 [inline]
>  __bpf_redirect_common net/core/filter.c:2196 [inline]
>  __bpf_redirect+0x148c/0x1610 net/core/filter.c:2203
>  ____bpf_clone_redirect net/core/filter.c:2477 [inline]
>  bpf_clone_redirect+0x37e/0x500 net/core/filter.c:2447
>  ___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:2010
>  __bpf_prog_run512+0xc5/0xf0 kernel/bpf/core.c:2253
>  bpf_dispatcher_nop_func include/linux/bpf.h:1265 [inline]
>  __bpf_prog_run include/linux/filter.h:701 [inline]
>  bpf_prog_run include/linux/filter.h:708 [inline]
>  bpf_test_run+0x546/0xd20 net/bpf/test_run.c:434
>  bpf_prog_test_run_skb+0x182f/0x24d0 net/bpf/test_run.c:1095
>  bpf_prog_test_run+0x5e5/0xa30 kernel/bpf/syscall.c:4266
>  __sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5671
>  __do_sys_bpf kernel/bpf/syscall.c:5760 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5758 [inline]
>  __x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5758
>  x64_sys_call+0x2cce/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:322
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Uninit was created at:
>  slab_post_alloc_hook mm/slub.c:4091 [inline]
>  slab_alloc_node mm/slub.c:4134 [inline]
>  kmem_cache_alloc_node_noprof+0x6bf/0xb80 mm/slub.c:4186
>  kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:587
>  pskb_expand_head+0x226/0x1a60 net/core/skbuff.c:2275
>  skb_ensure_writable+0x496/0x520 net/core/skbuff.c:6214
>  __bpf_try_make_writable net/core/filter.c:1677 [inline]
>  bpf_try_make_writable net/core/filter.c:1683 [inline]
>  bpf_try_make_head_writable net/core/filter.c:1691 [inline]
>  ____bpf_clone_redirect net/core/filter.c:2471 [inline]
>  bpf_clone_redirect+0x1c5/0x500 net/core/filter.c:2447
>  ___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:2010
>  __bpf_prog_run512+0xc5/0xf0 kernel/bpf/core.c:2253
>  bpf_dispatcher_nop_func include/linux/bpf.h:1265 [inline]
>  __bpf_prog_run include/linux/filter.h:701 [inline]
>  bpf_prog_run include/linux/filter.h:708 [inline]
>  bpf_test_run+0x546/0xd20 net/bpf/test_run.c:434
>  bpf_prog_test_run_skb+0x182f/0x24d0 net/bpf/test_run.c:1095
>  bpf_prog_test_run+0x5e5/0xa30 kernel/bpf/syscall.c:4266
>  __sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5671
>  __do_sys_bpf kernel/bpf/syscall.c:5760 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5758 [inline]
>  __x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5758
>  x64_sys_call+0x2cce/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:322
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> CPU: 1 UID: 0 PID: 8041 Comm: syz.2.760 Not tainted 6.12.0-rc6-syzkaller-00279-gde2f378f2b77 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
> =====================================================
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
>