[syzbot] [net?] KMSAN: uninit-value in IP6_ECN_decapsulate (3)
From: syzbot <hidden>
Date: 2026-01-07 16:24:22
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Hello, syzbot found the following issue on: HEAD commit: 9bb956508c9d Merge tag 'riscv-for-linus-6.18-rc3' of git:/.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=157ccbe2580000 kernel config: https://syzkaller.appspot.com/x/.config?x=dce7eac4016da338 dashboard link: https://syzkaller.appspot.com/bug?extid=d4dda070f833dc5dc89a compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12022258580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=140eaf34580000 Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/e72b2dd5c2f0/disk-9bb95650.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/a1b145971798/vmlinux-9bb95650.xz kernel image: https://storage.googleapis.com/syzbot-assets/bb711e135af2/bzImage-9bb95650.xz IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+d4dda070f833dc5dc89a@syzkaller.appspotmail.com syz.0.17 uses obsolete (PF_INET,SOCK_PACKET) ===================================================== BUG: KMSAN: uninit-value in __INET_ECN_decapsulate include/net/inet_ecn.h:253 [inline] BUG: KMSAN: uninit-value in INET_ECN_decapsulate include/net/inet_ecn.h:275 [inline] BUG: KMSAN: uninit-value in IP6_ECN_decapsulate+0x7a8/0x1fa0 include/net/inet_ecn.h:321 __INET_ECN_decapsulate include/net/inet_ecn.h:253 [inline] INET_ECN_decapsulate include/net/inet_ecn.h:275 [inline] IP6_ECN_decapsulate+0x7a8/0x1fa0 include/net/inet_ecn.h:321 ip6ip6_dscp_ecn_decapsulate+0x16f/0x1b0 net/ipv6/ip6_tunnel.c:729 __ip6_tnl_rcv+0xed9/0x1b50 net/ipv6/ip6_tunnel.c:860 ip6_tnl_rcv+0xc3/0x100 net/ipv6/ip6_tunnel.c:903 gre_rcv+0x14fd/0x1b60 net/ipv6/ip6_gre.c:-1 ip6_protocol_deliver_rcu+0x1c89/0x2c60 net/ipv6/ip6_input.c:438 ip6_input_finish+0x1f4/0x4a0 net/ipv6/ip6_input.c:489 NF_HOOK include/linux/netfilter.h:318 [inline] ip6_input+0x9c/0x330 net/ipv6/ip6_input.c:500 ip6_mc_input+0x7ca/0xc10 net/ipv6/ip6_input.c:590 dst_input include/net/dst.h:474 [inline] ip6_rcv_finish+0x958/0x990 net/ipv6/ip6_input.c:79 NF_HOOK include/linux/netfilter.h:318 [inline] ipv6_rcv+0xf1/0x3c0 net/ipv6/ip6_input.c:311 __netif_receive_skb_one_core net/core/dev.c:6079 [inline] __netif_receive_skb+0x1df/0xac0 net/core/dev.c:6192 netif_receive_skb_internal net/core/dev.c:6278 [inline] netif_receive_skb+0x57/0x630 net/core/dev.c:6337 tun_rx_batched+0x1df/0x980 drivers/net/tun.c:1485 tun_get_user+0x5d60/0x6d70 drivers/net/tun.c:1953 tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0xbe2/0x15d0 fs/read_write.c:686 ksys_write fs/read_write.c:738 [inline] __do_sys_write fs/read_write.c:749 [inline] __se_sys_write fs/read_write.c:746 [inline] __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746 x64_sys_call+0x3014/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:2 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xd9/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f Uninit was created at: slab_post_alloc_hook mm/slub.c:4977 [inline] slab_alloc_node mm/slub.c:5280 [inline] kmem_cache_alloc_node_noprof+0x989/0x16b0 mm/slub.c:5332 kmalloc_reserve+0x13c/0x4b0 net/core/skbuff.c:579 __alloc_skb+0x347/0x7d0 net/core/skbuff.c:670 alloc_skb include/linux/skbuff.h:1383 [inline] alloc_skb_with_frags+0xc5/0xa60 net/core/skbuff.c:6671 sock_alloc_send_pskb+0xacc/0xc60 net/core/sock.c:2965 tun_alloc_skb drivers/net/tun.c:1461 [inline] tun_get_user+0x1142/0x6d70 drivers/net/tun.c:1794 tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0xbe2/0x15d0 fs/read_write.c:686 ksys_write fs/read_write.c:738 [inline] __do_sys_write fs/read_write.c:749 [inline] __se_sys_write fs/read_write.c:746 [inline] __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746 x64_sys_call+0x3014/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:2 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xd9/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f CPU: 1 UID: 0 PID: 6032 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(none) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025 ===================================================== --- 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 syzbot to run the reproducer, reply with: #syz test: git://repo/address.git branch-or-commit-hash If you attach or paste a git patch, syzbot will apply it before testing. 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