Description

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...

Classification

CVE ID: CVE-2025-21858

Affected Products

Vendor: Linux, Linux

Product: Linux, Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.02% (probability of being exploited)

EPSS Percentile: 2.23% (scored less or equal to compared to others)

EPSS Date: 2025-04-10 (when was this score calculated)

References

https://nvd.nist.gov/vuln/detail/CVE-2025-21858
https://git.kernel.org/stable/c/904e746b2e7fa952ab8801b303ce826a63153d78
https://git.kernel.org/stable/c/3ce92ca990cfac88a87c61df3cc0b5880e688ecf
https://git.kernel.org/stable/c/da9b0ae47f084014b1e4b3f31f70a0defd047ff3
https://git.kernel.org/stable/c/788dbca056a8783ec063da3c9d49a3a71c76c283
https://git.kernel.org/stable/c/9593172d93b9f91c362baec4643003dc29802929

Timeline