syzkaller reported a null-ptr-deref while accessing sk2->sk_reuseport_cb
in reuseport_add_sock(). [0]
The repro first creates a listener with SO_REUSEPORT. Then, it creates
another listener on the same port and concurrently close()s the first
listener.
The second listen() calls reuseport_add_sock() with the first listener as
sk2, where sk2 is not expected to be cleared concurrently, but the close()
does clear it.
The assumption in reuseport_add_sock() is correct for TCP/UDP, which
serialises the changes to sk_reuseport_cb by holding the hash bucket
lock.
However, __sctp_hash_endpoint() does not hold sctp_hashbucket.lock before
calling reuseport_add_sock() , nor __sctp_unhash_endpoint() does before
reuseport_detach_sock().
Let's fix it by acquiring the bucket lock before reuseport_add_sock() and
reuseport_detach_sock().
[0]:
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
CPU: 1 UID: 0 PID: 10230 Comm: syz-executor119 Not tainted 6.10.0-syzkaller-12585-g301927d2d2eb #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
RIP: 0010:reuseport_add_sock+0x27e/0x5e0 net/core/sock_reuseport.c:350
Code: 00 0f b7 5d 00 bf 01 00 00 00 89 de e8 1b a4 ff f7 83 fb 01 0f 85 a3 01 00 00 e8 6d a0 ff f7 49 8d 7e 12 48 89 f8 48 c1 e8 03 <42> 0f b6 04 28 84 c0 0f 85 4b 02 00 00 41 0f b7 5e 12 49 8d 7e 14
RSP: 0018:ffffc9000b947c98 EFLAGS: 00010202
RAX: 0000000000000002 RBX: ffff8880252ddf98 RCX: ffff888079478000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000012
RBP: 0000000000000001 R08: ffffffff8993e18d R09: 1ffffffff1fef385
R10: dffffc0000000000 R11: fffffbfff1fef386 R12: ffff8880252ddac0
R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 00007f24e45b96c0(0000) GS:ffff8880b9300000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffcced5f7b8 CR3: 00000000241be000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__sctp_hash_endpoint net/sctp/input.c:762 [inline]
sctp_hash_endpoint+0x52a/0x600 net/sctp/input.c:790
sctp_listen_start net/sctp/socket.c:8570 [inline]
sctp_inet_listen+0x767/0xa20 net/sctp/socket.c:8625
__sys_listen_socket net/socket.c:1883 [inline]
__sys_listen+0x1b7/0x230 net/socket.c:1894
__do_sys_listen net/socket.c:1902 [inline]
__se_sys_listen net/socket.c:1900 [inline]
__x64_sys_listen+0x5a/0x70 net/socket.c:1900
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f24e46039b9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 91 1a 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f24e45b9228 EFLAGS: 00000246 ORIG_RAX: 0000000000000032
RAX: ffffffffffffffda RBX: 00007f24e468e428 RCX: 00007f24e46039b9
RDX: 00007f24e46039b9 RSI: 0000000000000003 RDI: 0000000000000004
RBP: 00007f24e468e420 R08: 00007f24e45b96c0 R09: 00007f24e45b96c0
R10: 00007f24e45b96c0 R11: 0000000000000246 R12: 00007f24e468e42c
R13: 00007f24e465a5dc R14: 0020000000000001 R15: 00007ffcced5f7d8
</TASK>
Modules linked in:
Fixes: 6ba845740267 ("sctp: process sk_reuseport in sctp_get_port_local")
Reported-by: syzbot+e6979a5d2f10ecb700e4@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=e6979a5d2f10ecb700e4
Tested-by: syzbot+e6979a5d2f10ecb700e4@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
---
net/sctp/input.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)
diff --git a/net/sctp/input.c b/net/sctp/input.c
index 17fcaa9b0df9..a8a254a5008e 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -735,15 +735,19 @@ static int __sctp_hash_endpoint(struct sctp_endpoint *ep)
struct sock *sk = ep->base.sk;
struct net *net = sock_net(sk);
struct sctp_hashbucket *head;
+ int err = 0;
ep->hashent = sctp_ep_hashfn(net, ep->base.bind_addr.port);
head = &sctp_ep_hashtable[ep->hashent];
+ write_lock(&head->lock);
if (sk->sk_reuseport) {
bool any = sctp_is_ep_boundall(sk);
struct sctp_endpoint *ep2;
struct list_head *list;
- int cnt = 0, err = 1;
+ int cnt = 0;
+
+ err = 1;
list_for_each(list, &ep->base.bind_addr.address_list)
cnt++;
@@ -761,24 +765,24 @@ static int __sctp_hash_endpoint(struct sctp_endpoint *ep)
if (!err) {
err = reuseport_add_sock(sk, sk2, any);
if (err)
- return err;
+ goto out;
break;
} else if (err < 0) {
- return err;
+ goto out;
}
}
if (err) {
err = reuseport_alloc(sk, any);
if (err)
- return err;
+ goto out;
}
}
- write_lock(&head->lock);
hlist_add_head(&ep->node, &head->chain);
+out:
write_unlock(&head->lock);
- return 0;
+ return err;
}
/* Add an endpoint to the hash. Local BH-safe. */
@@ -803,10 +807,9 @@ static void __sctp_unhash_endpoint(struct sctp_endpoint *ep)
head = &sctp_ep_hashtable[ep->hashent];
+ write_lock(&head->lock);
if (rcu_access_pointer(sk->sk_reuseport_cb))
reuseport_detach_sock(sk);
-
- write_lock(&head->lock);
hlist_del_init(&ep->node);
write_unlock(&head->lock);
}
--
2.30.2
