CVE-2021-47555 (GCVE-0-2021-47555)

Vulnerability from cvelistv5 – Published: 2024-05-24 15:09 – Updated: 2026-08-05 08:48
VLAI
Title
net: vlan: fix underflow for the real_dev refcnt
Summary
In the Linux kernel, the following vulnerability has been resolved: net: vlan: fix underflow for the real_dev refcnt Inject error before dev_hold(real_dev) in register_vlan_dev(), and execute the following testcase: ip link add dev dummy1 type dummy ip link add name dummy1.100 link dummy1 type vlan id 100 ip link del dev dummy1 When the dummy netdevice is removed, we will get a WARNING as following: ======================================================================= refcount_t: decrement hit 0; leaking memory. WARNING: CPU: 2 PID: 0 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 and an endless loop of: ======================================================================= unregister_netdevice: waiting for dummy1 to become free. Usage count = -1073741824 That is because dev_put(real_dev) in vlan_dev_free() be called without dev_hold(real_dev) in register_vlan_dev(). It makes the refcnt of real_dev underflow. Move the dev_hold(real_dev) to vlan_dev_init() which is the call-back of ndo_init(). That makes dev_hold() and dev_put() for vlan's real_dev symmetrical.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
4.4 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-05-29 16:50 UTC
CWE
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 700602b662d7eaa816b1a3cb0abe7a85de358fd4 , < 5e44178864b38dd70b877985abd7d86fdb95f27d (git)
Affected: e04a7a84bb77f9cdf4475340fe931389bc72331c , < 6e800ee43218a56acc93676bbb3d93b74779e555 (git)
Affected: 21032425c36ff85f16e72ca92193a8c401e4acd5 , < f7fc72a508cf115c273a7a29350069def1041890 (git)
Affected: 563bcbae3ba233c275c244bfce2efe12938f5363 , < 01d9cc2dea3fde3bad6d27f464eff463496e2b00 (git)
Affected: fca96b3f852a1b369b7b2844ce357cd689879934 (git)
Affected: 5.14.19 , < 5.15 (semver)
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Linux Linux Affected: 5.4.160 , < 5.4.163 (semver)
Affected: 5.10.80 , < 5.10.83 (semver)
Affected: 5.15.3 , < 5.15.6 (semver)
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        "descriptions": [
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: vlan: fix underflow for the real_dev refcnt\n\nInject error before dev_hold(real_dev) in register_vlan_dev(),\nand execute the following testcase:\n\nip link add dev dummy1 type dummy\nip link add name dummy1.100 link dummy1 type vlan id 100\nip link del dev dummy1\n\nWhen the dummy netdevice is removed, we will get a WARNING as following:\n\n=======================================================================\nrefcount_t: decrement hit 0; leaking memory.\nWARNING: CPU: 2 PID: 0 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0\n\nand an endless loop of:\n\n=======================================================================\nunregister_netdevice: waiting for dummy1 to become free. Usage count = -1073741824\n\nThat is because dev_put(real_dev) in vlan_dev_free() be called without\ndev_hold(real_dev) in register_vlan_dev(). It makes the refcnt of real_dev\nunderflow.\n\nMove the dev_hold(real_dev) to vlan_dev_init() which is the call-back of\nndo_init(). That makes dev_hold() and dev_put() for vlan\u0027s real_dev\nsymmetrical."
          },
          {
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            "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: net: vlan: corrige el desbordamiento insuficiente para real_dev refcnt Inyecte el error antes de dev_hold(real_dev) en Register_vlan_dev() y ejecute el siguiente caso de prueba: ip link add dev dummy1 tipo dummy ip link add nombre dummy1.100 link dummy1 tipo vlan id 100 ip link del dev dummy1 Cuando se elimina el dispositivo de red ficticio, recibiremos una ADVERTENCIA como la siguiente: ===================== ==================================================== = refcount_t: decremento hit 0; p\u00e9rdida de memoria. ADVERTENCIA: CPU: 2 PID: 0 en lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 y un bucle sin fin de: ======================== ================================================= unregister_netdevice: esperando que el dummy1 quede libre. Recuento de uso = -1073741824 Esto se debe a que dev_put(real_dev) en vlan_dev_free() se llama sin dev_hold(real_dev) en Register_vlan_dev(). Hace que el refcnt de real_dev se desborde. Mueva dev_hold(real_dev) a vlan_dev_init() que es la devoluci\u00f3n de llamada de ndo_init(). Eso hace que dev_hold() y dev_put() para real_dev de vlan sean sim\u00e9tricos."
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      "product_status:known_affected": "42",
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      "title": "kernel: net: vlan: fix underflow for the real_dev refcnt",
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      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2021-47555",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-47555.json",
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                  "value": "AV:L - The bug is reached only through local RTNL/ioctl VLAN creation (RTM_NEWLINK \u2192 vlan_newlink \u2192 register_vlan_dev, or ADD_VLAN_CMD), not via received packets or a remote protocol handler.\nAC:L - An attacker can reliably force the vulnerable error path after register_netdevice()/ndo_init by making netdev_upper_dev_link() fail (e.g. nesting past MAX_NEST_DEV=8), so vlan_dev_free() runs dev_put(real_dev) without a matching hold.\nPR:L - Creating VLAN devices requires CAP_NET_ADMIN checked with netlink_ns_capable()/ns_capable() against the netns user_ns, which an unprivileged user can obtain via user namespaces (unshare -Urn) with dummy/veth+vlan inside the new netns.\nUI:N - The attacker creates and tears down their own netdevices to trigger the underflow; no separate victim action is required.\nS:U - Impact is confined to the local host kernel (netdev refcnt underflow/UAF/DoS) and does not cross a VM, IOMMU, or other security-authority boundary.\nC:H - The extra dev_put() undercounts real_dev; when the displayed refcnt hits 1 while another holder still exists, wait_allrefs can free the net_device early (UAF), enabling heap reuse and kernel memory disclosure via netdev_ops/adjacent state.\nI:H - A use-after-free of struct net_device is exploitable for heap corruption and control-flow hijack (function pointers in netdev_ops and related objects), matching UAF integrity guidance.\nA:H - The demonstrated impact is refcount saturation/underflow leading to an endless unregister_netdevice wait (Usage count stuck) or a kernel oops on UAF, either of which is a full availability loss."
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}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.