Message-ID: <2025102817-CVE-2025-40064-0c16@gregkh>
Date: Tue, 28 Oct 2025 12:48:41 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40064: smc: Fix use-after-free in __pnet_find_base_ndev().

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

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

smc: Fix use-after-free in __pnet_find_base_ndev().

syzbot reported use-after-free of net_device in __pnet_find_base_ndev(),
which was called during connect(). [0]

smc_pnet_find_ism_resource() fetches sk_dst_get(sk)->dev and passes
down to pnet_find_base_ndev(), where RTNL is held.  Then, UAF happened
at __pnet_find_base_ndev() when the dev is first used.

This means dev had already been freed before acquiring RTNL in
pnet_find_base_ndev().

While dev is going away, dst->dev could be swapped with blackhole_netdev,
and the dev's refcnt by dst will be released.

We must hold dev's refcnt before calling smc_pnet_find_ism_resource().

Also, smc_pnet_find_roce_resource() has the same problem.

Let's use __sk_dst_get() and dst_dev_rcu() in the two functions.

[0]:
BUG: KASAN: use-after-free in __pnet_find_base_ndev+0x1b1/0x1c0 net/smc/smc_pnet.c:926
Read of size 1 at addr ffff888036bac33a by task syz.0.3632/18609

CPU: 1 UID: 0 PID: 18609 Comm: syz.0.3632 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 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+0x118/0x150 mm/kasan/report.c:595
 __pnet_find_base_ndev+0x1b1/0x1c0 net/smc/smc_pnet.c:926
 pnet_find_base_ndev net/smc/smc_pnet.c:946 [inline]
 smc_pnet_find_ism_by_pnetid net/smc/smc_pnet.c:1103 [inline]
 smc_pnet_find_ism_resource+0xef/0x390 net/smc/smc_pnet.c:1154
 smc_find_ism_device net/smc/af_smc.c:1030 [inline]
 smc_find_proposal_devices net/smc/af_smc.c:1115 [inline]
 __smc_connect+0x372/0x1890 net/smc/af_smc.c:1545
 smc_connect+0x877/0xd90 net/smc/af_smc.c:1715
 __sys_connect_file net/socket.c:2086 [inline]
 __sys_connect+0x313/0x440 net/socket.c:2105
 __do_sys_connect net/socket.c:2111 [inline]
 __se_sys_connect net/socket.c:2108 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2108
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f47cbf8eba9
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:00007f47ccdb1038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f47cc1d5fa0 RCX: 00007f47cbf8eba9
RDX: 0000000000000010 RSI: 0000200000000280 RDI: 000000000000000b
RBP: 00007f47cc011e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f47cc1d6038 R14: 00007f47cc1d5fa0 R15: 00007ffc512f8aa8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888036bacd00 pfn:0x36bac
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001243d08 ffff8880b863fdc0 0000000000000000
raw: ffff888036bacd00 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x446dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP), pid 16741, tgid 16741 (syz-executor), ts 343313197788, free_ts 380670750466
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
 prep_new_page mm/page_alloc.c:1859 [inline]
 get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3858
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
 ___kmalloc_large_node+0x5f/0x1b0 mm/slub.c:4317
 __kmalloc_large_node_noprof+0x18/0x90 mm/slub.c:4348
 __do_kmalloc_node mm/slub.c:4364 [inline]
 __kvmalloc_node_noprof+0x6d/0x5f0 mm/slub.c:5067
 alloc_netdev_mqs+0xa3/0x11b0 net/core/dev.c:11812
 tun_set_iff+0x532/0xef0 drivers/net/tun.c:2775
 __tun_chr_ioctl+0x788/0x1df0 drivers/net/tun.c:3085
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 18610 tgid 18608 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2895
 free_large_kmalloc+0x13a/0x1f0 mm/slub.c:4820
 device_release+0x99/0x1c0 drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x22b/0x480 lib/kobject.c:737
 netdev_run_todo+0xd2e/0xea0 net/core/dev.c:11513
 rtnl_unlock net/core/rtnetlink.c:157 [inline]
 rtnl_net_unlock include/linux/rtnetlink.h:135 [inline]
 rtnl_dellink+0x537/0x710 net/core/rtnetlink.c:3563
 rtnetlink_rcv_msg+0x7cc/0xb70 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg+0x219/0x270 net/socket.c:729
 ____sys_sendmsg+0x505/0x830 net/socket.c:2614
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
 __sys_sendmsg net/socket.c:2700 [inline]
 __do_sys_sendmsg net/socket.c:2705 [inline]
 __se_sys_sendmsg net/socket.c:2703 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888036bac200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888036bac280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888036bac300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                        ^
 ffff888036bac380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888036bac400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

The Linux kernel CVE team has assigned CVE-2025-40064 to this issue.


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

	Issue introduced in 4.19 with commit 0afff91c6f5ecef27715ea71e34dc2baacba1060 and fixed in 6.17.3 with commit 233927b645cb7a14bb98d23ac72e4c7243a9f0d9
	Issue introduced in 4.19 with commit 0afff91c6f5ecef27715ea71e34dc2baacba1060 and fixed in 6.18-rc1 with commit 3d3466878afd8d43ec0ca2facfbc7f03e40d0f79

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-2025-40064
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/smc/smc_pnet.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/233927b645cb7a14bb98d23ac72e4c7243a9f0d9
	https://git.kernel.org/stable/c/3d3466878afd8d43ec0ca2facfbc7f03e40d0f79

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