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CVE-2024-26804

Vulnérabilité élevée dans Linux (Linux)

CVSS 7.8 · Élevée
EPSS 0.2%
Linux•Linux•Versions : <=6.1.*, 5.15.151, <2e95350fe9db9d53c701075060ac8ac883b68aee, 0, <ab63de24ebea36fe73ac7121738595d704b66d96, <f81e94d2dcd2397137edcb8b85f4c5bed5d22383, 6.7.9, <2.6.34, 6.8, <a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9, <049d7989c67e8dd50f07a2096dbafdb41331fb9b, 6.1.81, <=5.10.*, <=6.6.*, 2.6.34, 5.4.271, <=5.4.*, <5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f, <=*, 243aad830e8a4cdda261626fbaeddde16b08d04a, 5.10.212, <=5.15.*, <=6.7.*, 2.6.33.2, 6.6.21, <afec0c5cd2ed71ca95a8b36a5e6d03333bf34282, 03017375b0122453e6dda833ff7bd4191915def5

Description

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.

Gravité et risque d'exploitation

CVE-2024-26804 obtient un score CVSS de 7.8/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.25 %, ce qui la place devant 15.0 % des CVE référencées.

Que faire ?

  • Vérifiez si Linux (versions <=6.1.*, 5.15.151, <2e95350fe9db9d53c701075060ac8ac883b68aee, 0, <ab63de24ebea36fe73ac7121738595d704b66d96, <f81e94d2dcd2397137edcb8b85f4c5bed5d22383, 6.7.9, <2.6.34, 6.8, <a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9, <049d7989c67e8dd50f07a2096dbafdb41331fb9b, 6.1.81, <=5.10.*, <=6.6.*, 2.6.34, 5.4.271, <=5.4.*, <5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f, <=*, 243aad830e8a4cdda261626fbaeddde16b08d04a, 5.10.212, <=5.15.*, <=6.7.*, 2.6.33.2, 6.6.21, <afec0c5cd2ed71ca95a8b36a5e6d03333bf34282, 03017375b0122453e6dda833ff7bd4191915def5) est présent sur votre parc.
  • Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
  • À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
  • Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

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