CVE-2025-21858

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

geneve: Fix use-after-free in geneve_find_dev().

syzkaller reported a use-after-free in geneve_find_dev() [0]

without repro.

geneve_configure() links struct geneve_dev.next to

net_generic(net, geneve_net_id)->geneve_list.

The net here could differ from dev_net(dev) if IFLA_NET_NS_PID,

IFLA_NET_NS_FD, or IFLA_TARGET_NETNSID is set.

When dev_net(dev) is dismantled, geneve_exit_batch_rtnl() finally

calls unregister_netdevice_queue() for each dev in the netns,

and later the dev is freed.

However, its geneve_dev.next is still linked to the backend UDP

socket netns.

Then, use-after-free will occur when another geneve dev is created

in the netns.

Let's call geneve_dellink() instead in geneve_destroy_tunnels().

[0]:

BUG: KASAN: slab-use-after-free in geneve_find_dev drivers/net/geneve.c:1295 [inline]

BUG: KASAN: slab-use-after-free in geneve_configure+0x234/0x858 drivers/net/geneve.c:1343

Read of size 2 at addr ffff000054d6ee24 by task syz.1.4029/13441

CPU: 1 UID: 0 PID: 13441 Comm: syz.1.4029 Not tainted 6.13.0-g0ad9617c78ac #24 dc35ca22c79fb82e8e7bc5c9c9adafea898b1e3d

Hardware name: linux,dummy-virt (DT)

Call trace:

show_stack+0x38/0x50 arch/arm64/kernel/stacktrace.c:466 (C)

__dump_stack lib/dump_stack.c:94 [inline]

dump_stack_lvl+0xbc/0x108 lib/dump_stack.c:120

print_address_description mm/kasan/report.c:378 [inline]

print_report+0x16c/0x6f0 mm/kasan/report.c:489

kasan_report+0xc0/0x120 mm/kasan/report.c:602

__asan_report_load2_noabort+0x20/0x30 mm/kasan/report_generic.c:379

geneve_find_dev drivers/net/geneve.c:1295 [inline]

geneve_configure+0x234/0x858 drivers/net/geneve.c:1343

geneve_newlink+0xb8/0x128 drivers/net/geneve.c:1634

rtnl_newlink_create+0x23c/0x868 net/core/rtnetlink.c:3795

__rtnl_newlink net/core/rtnetlink.c:3906 [inline]

rtnl_newlink+0x1054/0x1630 net/core/rtnetlink.c:4021

rtnetlink_rcv_msg+0x61c/0x918 net/core/rtnetlink.c:6911

netlink_rcv_skb+0x1dc/0x398 net/netlink/af_netlink.c:2543

rtnetlink_rcv+0x34/0x50 net/core/rtnetlink.c:6938

netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]

netlink_unicast+0x618/0x838 net/netlink/af_netlink.c:1348

netlink_sendmsg+0x5fc/0x8b0 net/netlink/af_netlink.c:1892

sock_sendmsg_nosec net/socket.c:713 [inline]

__sock_sendmsg net/socket.c:728 [inline]

____sys_sendmsg+0x410/0x6f8 net/socket.c:2568

___sys_sendmsg+0x178/0x1d8 net/socket.c:2622

__sys_sendmsg net/socket.c:2654 [inline]

__do_sys_sendmsg net/socket.c:2659 [inline]

__se_sys_sendmsg net/socket.c:2657 [inline]

__arm64_sys_sendmsg+0x12c/0x1c8 net/socket.c:2657

__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]

invoke_syscall+0x90/0x278 arch/arm64/kernel/syscall.c:49

el0_svc_common+0x13c/0x250 arch/arm64/kernel/syscall.c:132

do_el0_svc+0x54/0x70 arch/arm64/kernel/syscall.c:151

el0_svc+0x4c/0xa8 arch/arm64/kernel/entry-common.c:744

el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:762

el0t_64_sync+0x198/0x1a0 arch/arm64/kernel/entry.S:600

Allocated by task 13247:

kasan_save_stack mm/kasan/common.c:47 [inline]

kasan_save_track+0x30/0x68 mm/kasan/common.c:68

kasan_save_alloc_info+0x44/0x58 mm/kasan/generic.c:568

poison_kmalloc_redzone mm/kasan/common.c:377 [inline]

__kasan_kmalloc+0x84/0xa0 mm/kasan/common.c:394

kasan_kmalloc include/linux/kasan.h:260 [inline]

__do_kmalloc_node mm/slub.c:4298 [inline]

__kmalloc_node_noprof+0x2a0/0x560 mm/slub.c:4304

__kvmalloc_node_noprof+0x9c/0x230 mm/util.c:645

alloc_netdev_mqs+0xb8/0x11a0 net/core/dev.c:11470

rtnl_create_link+0x2b8/0xb50 net/core/rtnetlink.c:3604

rtnl_newlink_create+0x19c/0x868 net/core/rtnetlink.c:3780

__rtnl_newlink net/core/rtnetlink.c:3906 [inline]

rtnl_newlink+0x1054/0x1630 net/core/rtnetlink.c:4021

rtnetlink_rcv_msg+0x61c/0x918 net/core/rtnetlink.c:6911

netlink_rcv_skb+0x1dc/0x398 net/netlink/af_netlink.c:2543

rtnetlink_rcv+0x34/0x50 net/core/rtnetlink.c:6938

netlink_unicast_kernel net/netlink/af_n

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