UBSAN: Undefined behaviour in ./include/net/route.h:239:2: member access within null pointer of type 'struct rtable'

[Paul Menzel]

Dear Linux folks,


Enabling the undefined behavior sanitizer and building GNU/Linux 
4.18-rc5+ (with some unrelated commits) with GCC 8.1.0 from Debian 
Sid/unstable, the warning below is shown.

> [    8.083532] ================================================================================
> [    8.083781] UBSAN: Undefined behaviour in ./include/net/route.h:239:2
> [    8.083953] member access within null pointer of type 'struct rtable'
> [    8.084128] CPU: 1 PID: 239 Comm: sd-resolve Not tainted 4.18.0-rc5-00316-g4864b68cedf2 #104
> [    8.084131] Hardware name: ASROCK E350M1/E350M1, BIOS TIMELESS 01/01/1970
> [    8.084133] Call Trace:
> [    8.084147]  dump_stack+0x55/0x89
> [    8.084154]  ubsan_epilogue+0xb/0x33
> [    8.084158]  handle_null_ptr_deref+0x7f/0x90
> [    8.084163]  __ubsan_handle_type_mismatch_v1+0x55/0x60
> [    8.084170]  udp_sendmsg+0xb05/0xf80
> [    8.084176]  ? ip_reply_glue_bits+0x80/0x80
> [    8.084185]  ? import_iovec+0x4a/0x160
> [    8.084190]  ? udp_lib_get_port+0x810/0x810
> [    8.084194]  inet_sendmsg+0x77/0x1d0
> [    8.084198]  ? inet_sk_set_state+0x110/0x110
> [    8.084203]  sock_sendmsg+0x5a/0xb0
> [    8.084207]  ___sys_sendmsg+0x102/0x390
> [    8.084214]  ? seccomp_run_filters+0x79/0x220
> [    8.084218]  ? ip4_datagram_release_cb+0x5f/0x2a0
> [    8.084222]  ? udp_lib_rehash+0x17c/0x300
> [    8.084228]  ? __fget_light+0x99/0x110
> [    8.084230]  ? __fdget+0x12/0x20
> [    8.084234]  ? sockfd_lookup_light+0x1e/0xc0
> [    8.084238]  __sys_sendmmsg+0xef/0x1d0
> [    8.084244]  ? alloc_file+0x9b/0x1e0
> [    8.084249]  ? __secure_computing+0x41/0x120
> [    8.084253]  ? syscall_trace_enter+0x1e5/0x470
> [    8.084258]  sys_sendmmsg+0x28/0x30
> [    8.084262]  do_fast_syscall_32+0xce/0x3e0
> [    8.084267]  entry_SYSENTER_32+0x4e/0x7c
> [    8.084272] EIP: 0xb7fabbb5
> [    8.084273] Code: 89 e5 8b 55 08 85 d2 8b 80 5c cd ff ff 74 02 89 02 5d c3 8b 04 24 c3 8b 1c 24 c3 8b 3c 24 c3 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d 76 00 58 b8 77 00 00 00 cd 80 90 8d 76 
> [    8.084339] EAX: ffffffda EBX: 0000000c ECX: b75d240c EDX: 00000002
> [    8.084342] ESI: 00004000 EDI: 00000000 EBP: 03fdd1f0 ESP: b75d22f0
> [    8.084345] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000282
> [    8.084349] ================================================================================


Kind regards,

Paul