Subject: CVE-2024-44935: sctp: Fix null-ptr-deref in reuseport_add_sock().

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

sctp: Fix null-ptr-deref in reuseport_add_sock().

syzbot 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 closes the first
listener.

The second listen() calls reuseport_add_sock() with the first listener as
sk2, where sk2->sk_reuseport_cb is not expected to be cleared concurrently,
but the close() does clear it by reuseport_detach_sock().

The problem is SCTP does not properly synchronise reuseport_alloc(),
reuseport_add_sock(), and reuseport_detach_sock().

The caller of reuseport_alloc() and reuseport_{add,detach}_sock() must
provide synchronisation for sockets that are classified into the same
reuseport group.

Otherwise, such sockets form multiple identical reuseport groups, and
all groups except one would be silently dead.

  1. Two sockets call listen() concurrently
  2. No socket in the same group found in sctp_ep_hashtable[]
  3. Two sockets call reuseport_alloc() and form two reuseport groups
  4. Only one group hit first in __sctp_rcv_lookup_endpoint() receives
      incoming packets

Also, the reported null-ptr-deref could occur.

TCP/UDP guarantees that would not happen by holding the hash bucket lock.

Let's apply the locking strategy to __sctp_hash_endpoint() and
__sctp_unhash_endpoint().

[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:

The Linux kernel CVE team has assigned CVE-2024-44935 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.0 with commit 6ba845740267 and fixed in 5.4.282 with commit c9b3fc4f1578
	Issue introduced in 5.0 with commit 6ba845740267 and fixed in 5.10.224 with commit 52319d9d2f52
	Issue introduced in 5.0 with commit 6ba845740267 and fixed in 5.15.165 with commit 54b303d8f970
	Issue introduced in 5.0 with commit 6ba845740267 and fixed in 6.1.105 with commit 05e4a0fa2482
	Issue introduced in 5.0 with commit 6ba845740267 and fixed in 6.6.46 with commit 1407be30fc17
	Issue introduced in 5.0 with commit 6ba845740267 and fixed in 6.10.5 with commit e809a84c8023
	Issue introduced in 5.0 with commit 6ba845740267 and fixed in 6.11 with commit 9ab0faa7f9ff

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-44935
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/sctp/input.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/c9b3fc4f157867e858734e31022ebee8a24f0de7
	https://git.kernel.org/stable/c/52319d9d2f522ed939af31af70f8c3a0f0f67e6c
	https://git.kernel.org/stable/c/54b303d8f9702b8ab618c5032fae886b16356928
	https://git.kernel.org/stable/c/05e4a0fa248240efd99a539853e844f0f0a9e6a5
	https://git.kernel.org/stable/c/1407be30fc17eff918a98e0a990c0e988f11dc84
	https://git.kernel.org/stable/c/e809a84c802377ef61525a298a1ec1728759b913
	https://git.kernel.org/stable/c/9ab0faa7f9ffe31296dbb9bbe6f76c72c14eea18