[PATCH v1 net-next] sctp: Don't inherit do_auto_asconf in sctp_clone_sock().

syzbot reported list_del(&sp->auto_asconf_list) corruption
in sctp_destroy_sock().

The repro calls setsockopt(SCTP_AUTO_ASCONF, 1) to a SCTP
listener, calls accept(), and close()s the child socket.

setsockopt(SCTP_AUTO_ASCONF, 1) sets sp->do_auto_asconf
to 1 and links sp->auto_asconf_list to a per-netns list.

Both fields are placed after sp->pd_lobby in struct sctp_sock,
and sctp_copy_descendant() did not copy the fields before the
cited commit.

Also, sctp_clone_sock() did not set them explicitly.

In addition, sctp_auto_asconf_init() is called from
sctp_sock_migrate(), but it initialises the fields only
conditionally.

The two fields relied on __GFP_ZERO added in sk_alloc(),
but sk_clone() does not use it.

Let's clear newsp->do_auto_asconf in sctp_clone_sock().

[0]:
list_del corruption. prev->next should be ffff8880799e9148, but was ffff8880799e8808. (prev=ffff88803347d9f8)
kernel BUG at lib/list_debug.c:64!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 6008 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:__list_del_entry_valid_or_report+0x15a/0x190 lib/list_debug.c:62
Code: e8 7b 26 71 fd 43 80 3c 2c 00 74 08 4c 89 ff e8 7c ee 92 fd 49 8b 17 48 c7 c7 80 0a bf 8b 48 89 de 4c 89 f9 e8 07 c6 94 fc 90 <0f> 0b 4c 89 f7 e8 4c 26 71 fd 43 80 3c 2c 00 74 08 4c 89 ff e8 4d
RSP: 0018:ffffc90003067ad8 EFLAGS: 00010246
RAX: 000000000000006d RBX: ffff8880799e9148 RCX: b056988859ee6e00
RDX: 0000000000000000 RSI: 0000000000000202 RDI: 0000000000000000
RBP: dffffc0000000000 R08: ffffc90003067807 R09: 1ffff9200060cf00
R10: dffffc0000000000 R11: fffff5200060cf01 R12: 1ffff1100668fb3f
R13: dffffc0000000000 R14: ffff88803347d9f8 R15: ffff88803347d9f8
FS:  00005555823e5500(0000) GS:ffff88812613e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000480 CR3: 00000000741ce000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __list_del_entry_valid include/linux/list.h:132 [inline]
 __list_del_entry include/linux/list.h:223 [inline]
 list_del include/linux/list.h:237 [inline]
 sctp_destroy_sock+0xb4/0x370 net/sctp/socket.c:5163
 sk_common_release+0x75/0x310 net/core/sock.c:3961
 sctp_close+0x77e/0x900 net/sctp/socket.c:1550
 inet_release+0x144/0x190 net/ipv4/af_inet.c:437
 __sock_release net/socket.c:662 [inline]
 sock_close+0xc3/0x240 net/socket.c:1455
 __fput+0x44c/0xa70 fs/file_table.c:468
 task_work_run+0x1d4/0x260 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop+0xe9/0x130 kernel/entry/common.c:43
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x2bd/0xfa0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: 16942cf4d3e3 ("sctp: Use sk_clone() in sctp_accept().")
Reported-by: [email protected]
Closes: https://lore.kernel.org/netdev/[email protected]/
Signed-off-by: Kuniyuki Iwashima <[email protected]>
---
 include/net/sctp/structs.h | 4 ----
 net/sctp/socket.c          | 1 +
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 5900196d65fd..affee44bd38e 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -228,10 +228,6 @@ struct sctp_sock {
 
 	atomic_t pd_mode;
 
-	/* Fields after this point will be skipped on copies, like on accept
-	 * and peeloff operations
-	 */
-
 	/* Receive to here while partial delivery is in effect. */
 	struct sk_buff_head pd_lobby;
 
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 38d2932acebf..d808096f5ab1 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4885,6 +4885,7 @@ static struct sock *sctp_clone_sock(struct sock *sk,
 	}
 #endif
 
+	newsp->do_auto_asconf = 0;
 	skb_queue_head_init(&newsp->pd_lobby);
 
 	newsp->ep = sctp_endpoint_new(newsk, GFP_KERNEL);
-- 
2.51.2.1041.gc1ab5b90ca-goog