syzbot reported the splat below. [0] Since the cited commit, the child socket inherits all fields of its parent socket unless explicitly cleared. syzbot set IP_OPTIONS to AF_INET6 socket and created a child socket inheriting inet_sk(sk)->inet_opt. sctp_v6_copy_ip_options() only clones np->opt, and leaving inet_opt results in double-free. Let's clear inet_opt in sctp_v6_copy_ip_options(). [0]: BUG: KASAN: double-free in inet_sock_destruct+0x538/0x740 net/ipv4/af_inet.c:159 Free of addr ffff8880304b6d40 by task ksoftirqd/0/15 CPU: 0 UID: 0 PID: 15 Comm: ksoftirqd/0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025 Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0xca/0x240 mm/kasan/report.c:482 kasan_report_invalid_free+0xea/0x110 mm/kasan/report.c:557 check_slab_allocation+0xe1/0x130 include/linux/page-flags.h:-1 kasan_slab_pre_free include/linux/kasan.h:198 [inline] slab_free_hook mm/slub.c:2484 [inline] slab_free mm/slub.c:6630 [inline] kfree+0x148/0x6d0 mm/slub.c:6837 inet_sock_destruct+0x538/0x740 net/ipv4/af_inet.c:159 __sk_destruct+0x89/0x660 net/core/sock.c:2350 sock_put include/net/sock.h:1991 [inline] sctp_endpoint_destroy_rcu+0xa1/0xf0 net/sctp/endpointola.c:197 rcu_do_batch kernel/rcu/tree.c:2605 [inline] rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861 handle_softirqs+0x286/0x870 kernel/softirq.c:622 run_ksoftirqd+0x9b/0x100 kernel/softirq.c:1063 smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 Allocated by task 6003: kasan_save_stack mm/kasan/common.c:56 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:77 poison_kmalloc_redzone mm/kasan/common.c:400 [inline] __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:417 kasan_kmalloc include/linux/kasan.h:262 [inline] __do_kmalloc_node mm/slub.c:5642 [inline] __kmalloc_noprof+0x411/0x7f0 mm/slub.c:5654 kmalloc_noprof include/linux/slab.h:961 [inline] kzalloc_noprof include/linux/slab.h:1094 [inline] ip_options_get+0x51/0x4c0 net/ipv4/ip_options.c:517 do_ip_setsockopt+0x1d9b/0x2d00 net/ipv4/ip_sockglue.c:1087 ip_setsockopt+0x66/0x110 net/ipv4/ip_sockglue.c:1417 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2360 __sys_setsockopt net/socket.c:2385 [inline] __do_sys_setsockopt net/socket.c:2391 [inline] __se_sys_setsockopt net/socket.c:2388 [inline] __x64_sys_setsockopt+0x13f/0x1b0 net/socket.c:2388 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task 15: kasan_save_stack mm/kasan/common.c:56 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:77 __kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:587 kasan_save_free_info mm/kasan/kasan.h:406 [inline] poison_slab_object mm/kasan/common.c:252 [inline] __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:284 kasan_slab_free include/linux/kasan.h:234 [inline] slab_free_hook mm/slub.c:2539 [inline] slab_free mm/slub.c:6630 [inline] kfree+0x19a/0x6d0 mm/slub.c:6837 inet_sock_destruct+0x538/0x740 net/ipv4/af_inet.c:159 __sk_destruct+0x89/0x660 net/core/sock.c:2350 sock_put include/net/sock.h:1991 [inline] sctp_endpoint_destroy_rcu+0xa1/0xf0 net/sctp/endpointola.c:197 rcu_do_batch kernel/rcu/tree.c:2605 [inline] rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861 handle_softirqs+0x286/0x870 kernel/softirq.c:622 run_ksoftirqd+0x9b/0x100 kernel/softirq.c:1063 smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 Fixes: 16942cf4d3e31 ("sctp: Use sk_clone() in sctp_accept().") Reported-by: syzbot+ec33a1a006ed5abe7309@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6936d112.a70a0220.38f243.00a8.GAE@google.com/ Signed-off-by: Kuniyuki Iwashima --- net/sctp/ipv6.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c index 069b7e45d8bda..531cb0690007a 100644 --- a/net/sctp/ipv6.c +++ b/net/sctp/ipv6.c @@ -492,6 +492,8 @@ static void sctp_v6_copy_ip_options(struct sock *sk, struct sock *newsk) struct ipv6_pinfo *newnp, *np = inet6_sk(sk); struct ipv6_txoptions *opt; + inet_sk(newsk)->inet_opt = NULL; + newnp = inet6_sk(newsk); rcu_read_lock(); -- 2.52.0.223.gf5cc29aaa4-goog