syzbot


KMSAN: uninit-value in ip6table_mangle_hook (3)

Status: upstream: reported C repro on 2024/11/22 14:42
Subsystems: netfilter
[Documentation on labels]
Reported-by: syzbot+6023ea32e206eef7920a@syzkaller.appspotmail.com
First crash: 563d, last: 33d
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
28402ec7-4dee-46b1-baec-a37a0360fbba assessment-security 💥 KMSAN: uninit-value in ip6table_mangle_hook (3) 2026/05/21 03:22 2026/05/21 03:22 2026/05/21 03:51 cf874a1cf36318c06202027159ddac14acf00db7 failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/7da674412b4e0984a7ea4fdf491c751f045579ec" "-s" "bzImage" "compile_commands.json"]: exit status 2 Root cause: ld.lld: error: undefined symbol: wcslen * * Restart config... * * * General architecture-dependent options * Kprobes (KPROBES) [N/y/?] n Optimize very unlikely/likely branches (JUMP_LABEL) [Y/n/?] y Static key selftest (STATIC_KEYS_SELFTEST) [N/y/?] n Static call selftest (STATIC_CALL_SELFTEST) [N/y/?] n Enable seccomp to safely execute untrusted bytecode (SECCOMP) [Y/n/?] y Show seccomp filter cache status in /proc/pid/seccomp_cache (SECCOMP_CACHE_DEBUG) [N/y/?] n Stack Protector buffer overflow detection (STACKPROTECTOR) [N/y/?] n Link Time Optimization (LTO) > 1. None (LTO_NONE) choice[1]: 1 Use Clang's Control Flow Integrity (CFI) (CFI_CLANG) [N/y/?] (NEW) Error in reading or end of file. Number of bits to use for ASLR of mmap base address (ARCH_MMAP_RND_BITS) [28] 28 Number of bits to use for ASLR of mmap base address for compatible applications (ARCH_MMAP_RND_COMPAT_BITS) [8] 8 MMU page size > 1. 4KiB pages (PAGE_SIZE_4KB) choice[1]: 1 Provide system calls for 32-bit time_t (COMPAT_32BIT_TIME) [Y/n/?] y Use a virtually-mapped stack (VMAP_STACK) [N/y/?] n Support for randomizing kernel stack offset on syscall entry (RANDOMIZE_KSTACK_OFFSET) [Y/n/?] y Default state of kernel stack offset randomization (RANDOMIZE_KSTACK_OFFSET_DEFAULT) [N/y/?] n Locking event counts collection (LOCK_EVENT_COUNTS) [N/y/?] n * * Memory initialization * Initialize kernel stack variables at function entry > 1. no automatic stack variable initialization (weakest) (INIT_STACK_NONE) choice[1]: 1 Enable register zeroing on function exit (ZERO_CALL_USED_REGS) [N/y/?] (NEW) Error in reading or end of file. * * Kernel hardening options * Randomize layout of sensitive kernel structures > 1. Disable structure layout randomization (RANDSTRUCT_NONE) 2. Fully randomize structure layout (RANDSTRUCT_FULL) (NEW) choice[1-2?]: Error in reading or end of file. * * Compile-time checks and compiler options * Debug information 1. Disable debug information (DEBUG_INFO_NONE) 2. Rely on the toolchain's implicit default DWARF version (DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT) > 3. Generate DWARF Version 4 debuginfo (DEBUG_INFO_DWARF4) 4. Generate DWARF Version 5 debuginfo (DEBUG_INFO_DWARF5) choice[1-4?]: 3 Reduce debugging information (DEBUG_INFO_REDUCED) [N/y/?] n Compressed Debug information > 1. Don't compress debug information (DEBUG_INFO_COMPRESSED_NONE) 2. Compress debugging information with zlib (DEBUG_INFO_COMPRESSED_ZLIB) 3. Compress debugging information with zstd (DEBUG_INFO_COMPRESSED_ZSTD) (NEW) choice[1-3?]: Error in reading or end of file. Produce split debuginfo in .dwo files (DEBUG_INFO_SPLIT) [N/y/?] n Generate BTF type information (DEBUG_INFO_BTF) [N/y/?] n Provide GDB scripts for kernel debugging (GDB_SCRIPTS) [N/y/?] n Warn for stack frames larger than (FRAME_WARN) [2048] 2048 Strip assembler-generated symbols during link (STRIP_ASM_SYMS) [N/y/?] n Install uapi headers to usr/include (HEADERS_INSTALL) [N/y/?] n Make section mismatch errors non-fatal (SECTION_MISMATCH_WARN_ONLY) [Y/n/?] y Force all function address 64B aligned (DEBUG_FORCE_FUNCTION_ALIGN_64B) [N/y/?] n Compile the kernel with frame pointers (FRAME_POINTER) [Y/?] y Compile-time stack metadata validation (STACK_VALIDATION) [N/y/?] n Generate vmlinux.map file when linking (VMLINUX_MAP) [N/y/?] n Force weak per-cpu definitions (DEBUG_FORCE_WEAK_PER_CPU) [N/y/?] n In file included from /app/workdir/cache/src/6c8506e6f531dbd90bdf79ec77aeb3020c3d3296/net/socket.c:108: In file included from /app/workdir/cache/src/6c8506e6f531dbd90bdf79ec77aeb3020c3d3296/include/net/busy_poll.h:18: /app/workdir/cache/src/6c8506e6f531dbd90bdf79ec77aeb3020c3d3296/include/net/ip.h:475:14: warning: default initialization of an object of type 'typeof (rt->dst.expires)' (aka 'const unsigned long') leav
Discussions (11)
Title Replies (including bot) Last reply
[syzbot] Monthly netfilter report (Apr 2026) 0 (1) 2026/04/29 20:32
[syzbot] Monthly netfilter report (Mar 2026) 0 (1) 2026/03/31 08:07
[PATCH net v3] ip6_gre: use skb_vlan_inet_prepare() instead of pskb_inet_may_pull() 5 (5) 2026/01/20 00:01
[PATCH v2 net] ip6_gre: use skb_vlan_inet_prepare() instead of pskb_inet_may_pull() 11 (11) 2026/01/12 15:24
[PATCH net] ip6_gre: use skb_vlan_inet_prepare() instead of pskb_inet_may_pull() 3 (3) 2026/01/05 20:50
[PATCH] ip6_tunnel: Fix uninit-value in ip6_tnl_xmit 5 (5) 2026/01/05 09:35
[syzbot] Monthly netfilter report (Jul 2025) 0 (1) 2025/07/20 09:04
[syzbot] Monthly netfilter report (Apr 2025) 0 (1) 2025/04/17 08:38
[syzbot] Monthly netfilter report (Feb 2025) 0 (1) 2025/02/13 12:34
[syzbot] [netfilter?] KMSAN: uninit-value in ip6table_mangle_hook (3) 0 (6) 2024/12/15 02:34
[syzbot] Monthly netfilter report (Dec 2024) 0 (1) 2024/12/13 13:16
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KMSAN: uninit-value in ip6table_mangle_hook netfilter 7 C 601 2937d 2968d 5/29 fixed on 2018/05/08 18:30
upstream KMSAN: uninit-value in ip6table_mangle_hook (2) netfilter 7 10 1783d 1860d 0/29 auto-closed as invalid on 2021/10/03 15:10
Last patch testing requests (15)
Created Duration User Patch Repo Result
2026/04/19 22:17 32m retest repro upstream report log
2026/04/19 22:02 27m retest repro upstream report log
2026/03/28 07:12 21m retest repro upstream report log
2026/02/08 21:10 21m retest repro upstream report log
2026/01/17 06:09 34m retest repro upstream report log
2025/11/30 12:12 22m retest repro upstream report log
2025/11/07 18:31 21m retest repro upstream report log
2025/09/21 07:59 1h30m retest repro upstream report log
2025/08/29 04:03 20m retest repro upstream report log
2025/07/13 07:14 29m retest repro upstream report log
2024/12/15 02:34 35m mazin@getstate.dev patch upstream OK log
2024/12/14 22:21 20m mazin@getstate.dev upstream report log
2024/12/14 22:16 1h09m mazin@getstate.dev patch upstream OK log
2024/12/03 15:28 21m dmantipov@yandex.ru patch https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git cdd30ebb1b9f36159d66f088b61aee264e649d7a report log
2024/12/03 13:28 23m dmantipov@yandex.ru patch https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git cdd30ebb1b9f36159d66f088b61aee264e649d7a report log

Sample crash report:
=====================================================
BUG: KMSAN: uninit-value in ip6t_mangle_out net/ipv6/netfilter/ip6table_mangle.c:56 [inline]
BUG: KMSAN: uninit-value in ip6table_mangle_hook+0x97d/0x9c0 net/ipv6/netfilter/ip6table_mangle.c:72
 ip6t_mangle_out net/ipv6/netfilter/ip6table_mangle.c:56 [inline]
 ip6table_mangle_hook+0x97d/0x9c0 net/ipv6/netfilter/ip6table_mangle.c:72
 nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
 nf_hook_slow+0xf4/0x400 net/netfilter/core.c:626
 nf_hook include/linux/netfilter.h:269 [inline]
 __ip6_local_out+0x5ac/0x640 net/ipv6/output_core.c:143
 ip6_local_out+0x4c/0x210 net/ipv6/output_core.c:153
 ip6tunnel_xmit+0x129/0x460 include/net/ip6_tunnel.h:161
 ip6_tnl_xmit+0x341a/0x3860 net/ipv6/ip6_tunnel.c:1281
 __gre6_xmit+0x14b9/0x1550 net/ipv6/ip6_gre.c:815
 ip6gre_xmit_ipv4 net/ipv6/ip6_gre.c:839 [inline]
 ip6gre_tunnel_xmit+0x18f7/0x2030 net/ipv6/ip6_gre.c:922
 __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
 sch_direct_xmit+0x399/0xd40 net/sched/sch_generic.c:343
 __dev_xmit_skb net/core/dev.c:3825 [inline]
 __dev_queue_xmit+0x2fcf/0x56d0 net/core/dev.c:4398
 dev_queue_xmit include/linux/netdevice.h:3094 [inline]
 packet_xmit+0x9c/0x6c0 net/packet/af_packet.c:276
 packet_snd net/packet/af_packet.c:3145 [inline]
 packet_sendmsg+0x908b/0xa370 net/packet/af_packet.c:3177
 sock_sendmsg_nosec net/socket.c:729 [inline]
 __sock_sendmsg+0x30f/0x380 net/socket.c:744
 __sys_sendto+0x645/0x7f0 net/socket.c:2214
 __do_sys_sendto net/socket.c:2226 [inline]
 __se_sys_sendto net/socket.c:2222 [inline]
 __x64_sys_sendto+0x125/0x1d0 net/socket.c:2222
 x64_sys_call+0x3373/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:45
 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 stored to memory at:
 ip6_tnl_xmit+0x34f7/0x3860 net/ipv6/ip6_tunnel.c:1277
 __gre6_xmit+0x14b9/0x1550 net/ipv6/ip6_gre.c:815
 ip6gre_xmit_ipv4 net/ipv6/ip6_gre.c:839 [inline]
 ip6gre_tunnel_xmit+0x18f7/0x2030 net/ipv6/ip6_gre.c:922
 __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
 sch_direct_xmit+0x399/0xd40 net/sched/sch_generic.c:343
 __dev_xmit_skb net/core/dev.c:3825 [inline]
 __dev_queue_xmit+0x2fcf/0x56d0 net/core/dev.c:4398
 dev_queue_xmit include/linux/netdevice.h:3094 [inline]
 packet_xmit+0x9c/0x6c0 net/packet/af_packet.c:276
 packet_snd net/packet/af_packet.c:3145 [inline]
 packet_sendmsg+0x908b/0xa370 net/packet/af_packet.c:3177
 sock_sendmsg_nosec net/socket.c:729 [inline]
 __sock_sendmsg+0x30f/0x380 net/socket.c:744
 __sys_sendto+0x645/0x7f0 net/socket.c:2214
 __do_sys_sendto net/socket.c:2226 [inline]
 __se_sys_sendto net/socket.c:2222 [inline]
 __x64_sys_sendto+0x125/0x1d0 net/socket.c:2222
 x64_sys_call+0x3373/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:45
 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]
 __do_kmalloc_node mm/slub.c:4263 [inline]
 __kmalloc_node_track_caller_noprof+0x6c7/0xf90 mm/slub.c:4283
 kmalloc_reserve+0x23e/0x4a0 net/core/skbuff.c:609
 pskb_expand_head+0x226/0x1a60 net/core/skbuff.c:2275
 skb_realloc_headroom+0x140/0x2b0 net/core/skbuff.c:2355
 ip6_tnl_xmit+0x2106/0x3860 net/ipv6/ip6_tunnel.c:1227
 __gre6_xmit+0x14b9/0x1550 net/ipv6/ip6_gre.c:815
 ip6gre_xmit_ipv4 net/ipv6/ip6_gre.c:839 [inline]
 ip6gre_tunnel_xmit+0x18f7/0x2030 net/ipv6/ip6_gre.c:922
 __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
 sch_direct_xmit+0x399/0xd40 net/sched/sch_generic.c:343
 __dev_xmit_skb net/core/dev.c:3825 [inline]
 __dev_queue_xmit+0x2fcf/0x56d0 net/core/dev.c:4398
 dev_queue_xmit include/linux/netdevice.h:3094 [inline]
 packet_xmit+0x9c/0x6c0 net/packet/af_packet.c:276
 packet_snd net/packet/af_packet.c:3145 [inline]
 packet_sendmsg+0x908b/0xa370 net/packet/af_packet.c:3177
 sock_sendmsg_nosec net/socket.c:729 [inline]
 __sock_sendmsg+0x30f/0x380 net/socket.c:744
 __sys_sendto+0x645/0x7f0 net/socket.c:2214
 __do_sys_sendto net/socket.c:2226 [inline]
 __se_sys_sendto net/socket.c:2222 [inline]
 __x64_sys_sendto+0x125/0x1d0 net/socket.c:2222
 x64_sys_call+0x3373/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:45
 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: 5819 Comm: syz-executor359 Not tainted 6.12.0-rc6-syzkaller-00077-g2e1b3cc9d7f7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
=====================================================

Crashes (11):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2024/11/06 11:13 upstream 2e1b3cc9d7f7 3a465482 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-root KMSAN: uninit-value in ip6table_mangle_hook
2024/11/06 06:19 upstream 2e1b3cc9d7f7 3a465482 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-root KMSAN: uninit-value in ip6table_mangle_hook
2025/02/04 17:44 upstream 0de63bb7d919 8f267cef .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-root KMSAN: uninit-value in ip6table_mangle_hook
2024/11/30 05:22 upstream 509f806f7f70 68914665 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-root KMSAN: uninit-value in ip6table_mangle_hook
2024/11/30 05:21 upstream 509f806f7f70 68914665 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-root KMSAN: uninit-value in ip6table_mangle_hook
2024/11/06 02:06 upstream 2e1b3cc9d7f7 3a465482 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-root KMSAN: uninit-value in ip6table_mangle_hook
2024/11/06 02:06 upstream 2e1b3cc9d7f7 3a465482 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-root KMSAN: uninit-value in ip6table_mangle_hook
2024/11/30 17:51 upstream 2ba9f676d0a2 68914665 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-386-root KMSAN: uninit-value in ip6table_mangle_hook
2024/11/30 17:50 upstream 2ba9f676d0a2 68914665 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-386-root KMSAN: uninit-value in ip6table_mangle_hook
2024/11/30 17:46 upstream 2ba9f676d0a2 68914665 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-386-root KMSAN: uninit-value in ip6table_mangle_hook
2024/11/06 07:43 upstream 2e1b3cc9d7f7 3a465482 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-386-root KMSAN: uninit-value in ip6table_mangle_hook
* Struck through repros no longer work on HEAD.