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Message-ID: <2025032710-CVE-2025-21875-8eca@gregkh>
Date: Thu, 27 Mar 2025 15:58:09 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21875: mptcp: always handle address removal under msk socket lock

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

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

mptcp: always handle address removal under msk socket lock

Syzkaller reported a lockdep splat in the PM control path:

  WARNING: CPU: 0 PID: 6693 at ./include/net/sock.h:1711 sock_owned_by_me include/net/sock.h:1711 [inline]
  WARNING: CPU: 0 PID: 6693 at ./include/net/sock.h:1711 msk_owned_by_me net/mptcp/protocol.h:363 [inline]
  WARNING: CPU: 0 PID: 6693 at ./include/net/sock.h:1711 mptcp_pm_nl_addr_send_ack+0x57c/0x610 net/mptcp/pm_netlink.c:788
  Modules linked in:
  CPU: 0 UID: 0 PID: 6693 Comm: syz.0.205 Not tainted 6.14.0-rc2-syzkaller-00303-gad1b832bf1cf #0
  Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
  RIP: 0010:sock_owned_by_me include/net/sock.h:1711 [inline]
  RIP: 0010:msk_owned_by_me net/mptcp/protocol.h:363 [inline]
  RIP: 0010:mptcp_pm_nl_addr_send_ack+0x57c/0x610 net/mptcp/pm_netlink.c:788
  Code: 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc e8 ca 7b d3 f5 eb b9 e8 c3 7b d3 f5 90 0f 0b 90 e9 dd fb ff ff e8 b5 7b d3 f5 90 <0f> 0b 90 e9 3e fb ff ff 44 89 f1 80 e1 07 38 c1 0f 8c eb fb ff ff
  RSP: 0000:ffffc900034f6f60 EFLAGS: 00010283
  RAX: ffffffff8bee3c2b RBX: 0000000000000001 RCX: 0000000000080000
  RDX: ffffc90004d42000 RSI: 000000000000a407 RDI: 000000000000a408
  RBP: ffffc900034f7030 R08: ffffffff8bee37f6 R09: 0100000000000000
  R10: dffffc0000000000 R11: ffffed100bcc62e4 R12: ffff88805e6316e0
  R13: ffff88805e630c00 R14: dffffc0000000000 R15: ffff88805e630c00
  FS:  00007f7e9a7e96c0(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000001b2fd18ff8 CR3: 0000000032c24000 CR4: 00000000003526f0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   <TASK>
   mptcp_pm_remove_addr+0x103/0x1d0 net/mptcp/pm.c:59
   mptcp_pm_remove_anno_addr+0x1f4/0x2f0 net/mptcp/pm_netlink.c:1486
   mptcp_nl_remove_subflow_and_signal_addr net/mptcp/pm_netlink.c:1518 [inline]
   mptcp_pm_nl_del_addr_doit+0x118d/0x1af0 net/mptcp/pm_netlink.c:1629
   genl_family_rcv_msg_doit net/netlink/genetlink.c:1115 [inline]
   genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
   genl_rcv_msg+0xb1f/0xec0 net/netlink/genetlink.c:1210
   netlink_rcv_skb+0x206/0x480 net/netlink/af_netlink.c:2543
   genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
   netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]
   netlink_unicast+0x7f6/0x990 net/netlink/af_netlink.c:1348
   netlink_sendmsg+0x8de/0xcb0 net/netlink/af_netlink.c:1892
   sock_sendmsg_nosec net/socket.c:718 [inline]
   __sock_sendmsg+0x221/0x270 net/socket.c:733
   ____sys_sendmsg+0x53a/0x860 net/socket.c:2573
   ___sys_sendmsg net/socket.c:2627 [inline]
   __sys_sendmsg+0x269/0x350 net/socket.c:2659
   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: 0033:0x7f7e9998cde9
  Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48
  RSP: 002b:00007f7e9a7e9038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
  RAX: ffffffffffffffda RBX: 00007f7e99ba5fa0 RCX: 00007f7e9998cde9
  RDX: 000000002000c094 RSI: 0000400000000000 RDI: 0000000000000007
  RBP: 00007f7e99a0e2a0 R08: 0000000000000000 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
  R13: 0000000000000000 R14: 00007f7e99ba5fa0 R15: 00007fff49231088

Indeed the PM can try to send a RM_ADDR over a msk without acquiring
first the msk socket lock.

The bugged code-path comes from an early optimization: when there
are no subflows, the PM should (usually) not send RM_ADDR
notifications.

The above statement is incorrect, as without locks another process
could concurrent create a new subflow and cause the RM_ADDR generation.

Additionally the supposed optimization is not very effective even
performance-wise, as most mptcp sockets should have at least one
subflow: the MPC one.

Address the issue removing the buggy code path, the existing "slow-path"
will handle correctly even the edge case.

The Linux kernel CVE team has assigned CVE-2025-21875 to this issue.


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

	Issue introduced in 5.10 with commit b6c08380860b926752d57c8fa9911fa388c4b876 and fixed in 5.10.235 with commit 494ec285535632732eaa5786297a9ae4f731b5ff
	Issue introduced in 5.10 with commit b6c08380860b926752d57c8fa9911fa388c4b876 and fixed in 5.15.179 with commit 7cca31035c05819643ffb5d7518e9a331b3f6651
	Issue introduced in 5.10 with commit b6c08380860b926752d57c8fa9911fa388c4b876 and fixed in 6.1.130 with commit 8116fb4acd5d3f06cd37f84887dbe962b6703b1c
	Issue introduced in 5.10 with commit b6c08380860b926752d57c8fa9911fa388c4b876 and fixed in 6.6.81 with commit a05da2be18aae7e82572f8d795f41bb49f5dfc7d
	Issue introduced in 5.10 with commit b6c08380860b926752d57c8fa9911fa388c4b876 and fixed in 6.12.18 with commit 4124b782ec2b1e2e490cf0bbf10f53dfd3479890
	Issue introduced in 5.10 with commit b6c08380860b926752d57c8fa9911fa388c4b876 and fixed in 6.13.6 with commit 2c3de6dff4373f1036e003f49a32629359530bdb
	Issue introduced in 5.10 with commit b6c08380860b926752d57c8fa9911fa388c4b876 and fixed in 6.14 with commit f865c24bc55158313d5779fc81116023a6940ca3

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-2025-21875
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/mptcp/pm_netlink.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/494ec285535632732eaa5786297a9ae4f731b5ff
	https://git.kernel.org/stable/c/7cca31035c05819643ffb5d7518e9a331b3f6651
	https://git.kernel.org/stable/c/8116fb4acd5d3f06cd37f84887dbe962b6703b1c
	https://git.kernel.org/stable/c/a05da2be18aae7e82572f8d795f41bb49f5dfc7d
	https://git.kernel.org/stable/c/4124b782ec2b1e2e490cf0bbf10f53dfd3479890
	https://git.kernel.org/stable/c/2c3de6dff4373f1036e003f49a32629359530bdb
	https://git.kernel.org/stable/c/f865c24bc55158313d5779fc81116023a6940ca3

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