head and skb->data distance is more than 64k and skb->network_header (u16) has wrapped around. The bug is in the ip_tunnel infrastructure, which can cause dev->needed_headroom to increment ad infinitum. The syzkaller reproducer consists of packets getting routed via a gre tunnel, and route of gre encapsulated packets pointing at another (ipip) tunnel. The ipip encapsulation finds gre0 as next output device. This results in the following pattern: 1). First packet is to be sent out via gre0. Route lookup found an output device, ipip0. 2). ip_tunnel_xmit for gre0 bumps gre0->needed_headroom based on the future output device, rt.dev->needed_headroom (ipip0). 3). ip output / start_xmit moves skb on to ipip0. which runs the same code path again (xmit recursion). 4). Routing step for the post-gre0-encap packet finds gre0 as output device to use for ipip0 encapsulated packet. tunl0->needed_headroom is then incremented based on the (already bumped) gre0 device headroom. This repeats for every future packet: gre0->needed_headroom gets inflated because previous packets' ipip0 step incremented rt->dev (gre0) headroom, and ipip0 incremented because gre0 needed_headroom was increased. For each subsequent packet, gre/ipip0->needed_headroom grows until post-expand-head reallocations result in a skb->head/data distance of more than 64k. Once that happens, skb->network_header (u16) wraps around when pskb_expand_head tries to make sure that skb_network_offset() is unchanged after the headroom expansion/reallocation. After this skb_network_offset(skb) returns a different (and negative) result post headroom expansion. The next trip to neigh layer (or anything else that would __skb_pull the network header) makes skb->data point to a memory location outside skb->head area. v2: Cap the needed_headroom update to an arbitarily chosen upperlimit to prevent perpetual increase instead of dropping the headroom increment completely.">

CVE-2024-26804 : Détail

CVE-2024-26804

5.3
/
Moyen
Memory Corruption
0.04%V3
Network
2024-04-04
08h20 +00:00
2024-12-19
08h47 +00:00
CVE.org
NVD
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Descriptions du CVE

net: ip_tunnel: prevent perpetual headroom growth

In the Linux kernel, the following vulnerability has been resolved: net: ip_tunnel: prevent perpetual headroom growth syzkaller triggered following kasan splat: BUG: KASAN: use-after-free in __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 Read of size 1 at addr ffff88812fb4000e by task syz-executor183/5191 [..] kasan_report+0xda/0x110 mm/kasan/report.c:588 __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 skb_flow_dissect_flow_keys include/linux/skbuff.h:1514 [inline] ___skb_get_hash net/core/flow_dissector.c:1791 [inline] __skb_get_hash+0xc7/0x540 net/core/flow_dissector.c:1856 skb_get_hash include/linux/skbuff.h:1556 [inline] ip_tunnel_xmit+0x1855/0x33c0 net/ipv4/ip_tunnel.c:748 ipip_tunnel_xmit+0x3cc/0x4e0 net/ipv4/ipip.c:308 __netdev_start_xmit include/linux/netdevice.h:4940 [inline] netdev_start_xmit include/linux/netdevice.h:4954 [inline] xmit_one net/core/dev.c:3548 [inline] dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 __dev_queue_xmit+0x7c1/0x3d60 net/core/dev.c:4349 dev_queue_xmit include/linux/netdevice.h:3134 [inline] neigh_connected_output+0x42c/0x5d0 net/core/neighbour.c:1592 ... ip_finish_output2+0x833/0x2550 net/ipv4/ip_output.c:235 ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323 .. iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82 ip_tunnel_xmit+0x1dbc/0x33c0 net/ipv4/ip_tunnel.c:831 ipgre_xmit+0x4a1/0x980 net/ipv4/ip_gre.c:665 __netdev_start_xmit include/linux/netdevice.h:4940 [inline] netdev_start_xmit include/linux/netdevice.h:4954 [inline] xmit_one net/core/dev.c:3548 [inline] dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 ... The splat occurs because skb->data points past skb->head allocated area. This is because neigh layer does: __skb_pull(skb, skb_network_offset(skb)); ... but skb_network_offset() returns a negative offset and __skb_pull() arg is unsigned. IOW, we skb->data gets "adjusted" by a huge value. The negative value is returned because skb->head and skb->data distance is more than 64k and skb->network_header (u16) has wrapped around. The bug is in the ip_tunnel infrastructure, which can cause dev->needed_headroom to increment ad infinitum. The syzkaller reproducer consists of packets getting routed via a gre tunnel, and route of gre encapsulated packets pointing at another (ipip) tunnel. The ipip encapsulation finds gre0 as next output device. This results in the following pattern: 1). First packet is to be sent out via gre0. Route lookup found an output device, ipip0. 2). ip_tunnel_xmit for gre0 bumps gre0->needed_headroom based on the future output device, rt.dev->needed_headroom (ipip0). 3). ip output / start_xmit moves skb on to ipip0. which runs the same code path again (xmit recursion). 4). Routing step for the post-gre0-encap packet finds gre0 as output device to use for ipip0 encapsulated packet. tunl0->needed_headroom is then incremented based on the (already bumped) gre0 device headroom. This repeats for every future packet: gre0->needed_headroom gets inflated because previous packets' ipip0 step incremented rt->dev (gre0) headroom, and ipip0 incremented because gre0 needed_headroom was increased. For each subsequent packet, gre/ipip0->needed_headroom grows until post-expand-head reallocations result in a skb->head/data distance of more than 64k. Once that happens, skb->network_header (u16) wraps around when pskb_expand_head tries to make sure that skb_network_offset() is unchanged after the headroom expansion/reallocation. After this skb_network_offset(skb) returns a different (and negative) result post headroom expansion. The next trip to neigh layer (or anything else that would __skb_pull the network header) makes skb->data point to a memory location outside skb->head area. v2: Cap the needed_headroom update to an arbitarily chosen upperlimit to prevent perpetual increase instead of dropping the headroom increment completely.

Informations du CVE

Faiblesses connexes

CWE-ID Nom de la faiblesse Source
CWE-416 Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Métriques

Métriques Score Gravité CVSS Vecteur Source
V3.1 5.3 MEDIUM CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Base: Exploitabilty Metrics

The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component.

Attack Vector

This metric reflects the context by which vulnerability exploitation is possible.

Network

The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).

Attack Complexity

This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability.

Low

Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.

Privileges Required

This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability.

None

The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.

User Interaction

This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component.

None

The vulnerable system can be exploited without interaction from any user.

Base: Scope Metrics

The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope.

Scope

Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs.

Unchanged

An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.

Base: Impact Metrics

The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve.

Confidentiality Impact

This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability.

None

There is no loss of confidentiality within the impacted component.

Integrity Impact

This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information.

None

There is no loss of integrity within the impacted component.

Availability Impact

This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability.

Low

Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Temporal Metrics

The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability.

Environmental Metrics

These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.

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EPSS

EPSS est un modèle de notation qui prédit la probabilité qu'une vulnérabilité soit exploitée.

Score EPSS

Le modèle EPSS produit un score de probabilité compris entre 0 et 1 (0 et 100 %). Plus la note est élevée, plus la probabilité qu'une vulnérabilité soit exploitée est grande.

Percentile EPSS

Le percentile est utilisé pour classer les CVE en fonction de leur score EPSS. Par exemple, une CVE dans le 95e percentile selon son score EPSS est plus susceptible d'être exploitée que 95 % des autres CVE. Ainsi, le percentile sert à comparer le score EPSS d'une CVE par rapport à d'autres CVE.
EPSS First.org

Products Mentioned

Configuraton 0

Linux>>Linux_kernel >> Version From (including) 2.6.34 To (excluding) 5.4.271

Linux>>Linux_kernel >> Version From (including) 5.5 To (excluding) 5.10.212

Linux>>Linux_kernel >> Version From (including) 5.11 To (excluding) 5.15.151

Linux>>Linux_kernel >> Version From (including) 5.16 To (excluding) 6.1.81

Linux>>Linux_kernel >> Version From (including) 6.2 To (excluding) 6.6.21

Linux>>Linux_kernel >> Version From (including) 6.7 To (excluding) 6.7.9

Linux>>Linux_kernel >> Version 6.8

Linux>>Linux_kernel >> Version 6.8

Linux>>Linux_kernel >> Version 6.8

Linux>>Linux_kernel >> Version 6.8

Linux>>Linux_kernel >> Version 6.8

Linux>>Linux_kernel >> Version 6.8

Configuraton 0

Debian>>Debian_linux >> Version 10.0

Références