Re: [syzbot] [lvs?] KMSAN: uninit-value in do_output_route4

	Hello,

On Thu, 1 May 2025, syzbot wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    bc3372351d0c Merge tag 'for-6.15-rc3-tag' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12d64574580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fca45111586bf9a6
> dashboard link: https://syzkaller.appspot.com/bug?extid=04b9a82855c8aed20860
> compiler:       Debian clang version 15.0.6, Debian LLD 15.0.6
> userspace arch: i386
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/01b8968610a1/disk-bc337235.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/528a97652269/vmlinux-bc337235.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/768ed51bbb66/bzImage-bc337235.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email protected]
> 
> =====================================================
> BUG: KMSAN: uninit-value in do_output_route4+0x42c/0x4d0 net/netfilter/ipvs/ip_vs_xmit.c:147
>  do_output_route4+0x42c/0x4d0 net/netfilter/ipvs/ip_vs_xmit.c:147
>  __ip_vs_get_out_rt+0x403/0x21d0 net/netfilter/ipvs/ip_vs_xmit.c:330
>  ip_vs_tunnel_xmit+0x205/0x2380 net/netfilter/ipvs/ip_vs_xmit.c:1136
>  ip_vs_in_hook+0x1aa5/0x35b0 net/netfilter/ipvs/ip_vs_core.c:2063
>  nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
>  nf_hook_slow+0xf7/0x400 net/netfilter/core.c:626
>  nf_hook include/linux/netfilter.h:269 [inline]
>  __ip_local_out+0x758/0x7e0 net/ipv4/ip_output.c:118
>  ip_local_out net/ipv4/ip_output.c:127 [inline]
>  ip_send_skb+0x6a/0x3c0 net/ipv4/ip_output.c:1501
>  udp_send_skb+0xfda/0x1b70 net/ipv4/udp.c:1195
>  udp_sendmsg+0x2fe3/0x33c0 net/ipv4/udp.c:1483
>  inet_sendmsg+0x1fc/0x280 net/ipv4/af_inet.c:851
>  sock_sendmsg_nosec net/socket.c:712 [inline]
>  __sock_sendmsg+0x267/0x380 net/socket.c:727
>  ____sys_sendmsg+0x91b/0xda0 net/socket.c:2566
>  ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2620
>  __sys_sendmmsg+0x41d/0x880 net/socket.c:2702
>  __compat_sys_sendmmsg net/compat.c:360 [inline]
>  __do_compat_sys_sendmmsg net/compat.c:367 [inline]
>  __se_compat_sys_sendmmsg net/compat.c:364 [inline]
>  __ia32_compat_sys_sendmmsg+0xc8/0x140 net/compat.c:364
>  ia32_sys_call+0x3ffa/0x41f0 arch/x86/include/generated/asm/syscalls_32.h:346
>  do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
>  __do_fast_syscall_32+0xb0/0x110 arch/x86/entry/syscall_32.c:306
>  do_fast_syscall_32+0x38/0x80 arch/x86/entry/syscall_32.c:331
>  do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:369
>  entry_SYSENTER_compat_after_hwframe+0x84/0x8e
> 
> Uninit was created at:
>  slab_post_alloc_hook mm/slub.c:4167 [inline]
>  slab_alloc_node mm/slub.c:4210 [inline]
>  __kmalloc_cache_noprof+0x8fa/0xe00 mm/slub.c:4367
>  kmalloc_noprof include/linux/slab.h:905 [inline]
>  ip_vs_dest_dst_alloc net/netfilter/ipvs/ip_vs_xmit.c:61 [inline]
>  __ip_vs_get_out_rt+0x35d/0x21d0 net/netfilter/ipvs/ip_vs_xmit.c:323
>  ip_vs_tunnel_xmit+0x205/0x2380 net/netfilter/ipvs/ip_vs_xmit.c:1136
>  ip_vs_in_hook+0x1aa5/0x35b0 net/netfilter/ipvs/ip_vs_core.c:2063
>  nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
>  nf_hook_slow+0xf7/0x400 net/netfilter/core.c:626
>  nf_hook include/linux/netfilter.h:269 [inline]
>  __ip_local_out+0x758/0x7e0 net/ipv4/ip_output.c:118
>  ip_local_out net/ipv4/ip_output.c:127 [inline]
>  ip_send_skb+0x6a/0x3c0 net/ipv4/ip_output.c:1501
>  udp_send_skb+0xfda/0x1b70 net/ipv4/udp.c:1195
>  udp_sendmsg+0x2fe3/0x33c0 net/ipv4/udp.c:1483
>  inet_sendmsg+0x1fc/0x280 net/ipv4/af_inet.c:851
>  sock_sendmsg_nosec net/socket.c:712 [inline]
>  __sock_sendmsg+0x267/0x380 net/socket.c:727
>  ____sys_sendmsg+0x91b/0xda0 net/socket.c:2566
>  ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2620
>  __sys_sendmmsg+0x41d/0x880 net/socket.c:2702
>  __compat_sys_sendmmsg net/compat.c:360 [inline]
>  __do_compat_sys_sendmmsg net/compat.c:367 [inline]
>  __se_compat_sys_sendmmsg net/compat.c:364 [inline]
>  __ia32_compat_sys_sendmmsg+0xc8/0x140 net/compat.c:364
>  ia32_sys_call+0x3ffa/0x41f0 arch/x86/include/generated/asm/syscalls_32.h:346
>  do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
>  __do_fast_syscall_32+0xb0/0x110 arch/x86/entry/syscall_32.c:306
>  do_fast_syscall_32+0x38/0x80 arch/x86/entry/syscall_32.c:331
>  do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:369
>  entry_SYSENTER_compat_after_hwframe+0x84/0x8e
> 
> CPU: 0 UID: 0 PID: 22408 Comm: syz.4.5165 Not tainted 6.15.0-rc3-syzkaller-00019-gbc3372351d0c #0 PREEMPT(undef) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
> =====================================================

	I hopefully addressed this report with patch titled
"ipvs: fix uninit-value for saddr in do_output_route4".

Regards

--
Julian Anastasov <[email protected]>