CVE-2021-47162

Description

In the Linux kernel, the following vulnerability has been resolved: tipc: skb_linearize the head skb when reassembling msgs It's not a good idea to append the frag skb to a skb's frag_list if the frag_list already has skbs from elsewhere, such as this skb was created by pskb_copy() where the frag_list was cloned (all the skbs in it were skb_get'ed) and shared by multiple skbs. However, the new appended frag skb should have been only seen by the current skb. Otherwise, it will cause use after free crashes as this appended frag skb are seen by multiple skbs but it only got skb_get called once. The same thing happens with a skb updated by pskb_may_pull() with a skb_cloned skb. Li Shuang has reported quite a few crashes caused by this when doing testing over macvlan devices: [] kernel BUG at net/core/skbuff.c:1970! [] Call Trace: [] skb_clone+0x4d/0xb0 [] macvlan_broadcast+0xd8/0x160 [macvlan] [] macvlan_process_broadcast+0x148/0x150 [macvlan] [] process_one_work+0x1a7/0x360 [] worker_thread+0x30/0x390 [] kernel BUG at mm/usercopy.c:102! [] Call Trace: [] __check_heap_object+0xd3/0x100 [] __check_object_size+0xff/0x16b [] simple_copy_to_iter+0x1c/0x30 [] __skb_datagram_iter+0x7d/0x310 [] __skb_datagram_iter+0x2a5/0x310 [] skb_copy_datagram_iter+0x3b/0x90 [] tipc_recvmsg+0x14a/0x3a0 [tipc] [] ____sys_recvmsg+0x91/0x150 [] ___sys_recvmsg+0x7b/0xc0 [] kernel BUG at mm/slub.c:305! [] Call Trace: [] <IRQ> [] kmem_cache_free+0x3ff/0x400 [] __netif_receive_skb_core+0x12c/0xc40 [] ? kmem_cache_alloc+0x12e/0x270 [] netif_receive_skb_internal+0x3d/0xb0 [] ? get_rx_page_info+0x8e/0xa0 [be2net] [] be_poll+0x6ef/0xd00 [be2net] [] ? irq_exit+0x4f/0x100 [] net_rx_action+0x149/0x3b0 ... This patch is to fix it by linearizing the head skb if it has frag_list set in tipc_buf_append(). Note that we choose to do this before calling skb_unshare(), as __skb_linearize() will avoid skb_copy(). Also, we can not just drop the frag_list either as the early time.

Gravité et risque d'exploitation

CVE-2021-47162 obtient un score CVSS de 9.8/10, soit une gravité critique. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.74 %, ce qui la place devant 53.9 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <4.3, 4.9.271, <4.2, <6da24cfc83ba4f97ea44fc7ae9999a006101755c, 0, <64d17ec9f1ded042c4b188d15734f33486ed9966, 4.14.235, <b2c8d28c34b3070407cb1741f9ba3f15d0284b8b, <=4.9.*, 4.4.271, 5.12.9, <=5.10.*, <=4.14.*, c19282fd54a19e4651a4e67836cd842082546677, 4.19.193, 5.10.42, <5489f30bb78ff0dafb4229a69632afc2ba20765c, <=5.4.*, <436d650d374329a591c30339a91fa5078052ed1e, 5.13, <=4.19.*, <=5.12.*, 4.1.14, <b7df21cf1b79ab7026f545e7bf837bd5750ac026, 4.3, 4.2.7, d45ed6c1ff20d3640a31f03816ca2d48fb7d6f22, <=4.4.*, <=*, <ace300eecbccaa698e2b472843c74a5f33f7dce8, 5.4.124, <4b1761898861117c97066aea6c58f68a7787f0bf, 45c8b7b175ceb2d542e0fe15247377bf3bce29ec) 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

• https://git.kernel.org/stable/c/b2c8d28c34b3070407cb1741f9ba3f15d0284b8b
• https://git.kernel.org/stable/c/5489f30bb78ff0dafb4229a69632afc2ba20765c
• https://git.kernel.org/stable/c/436d650d374329a591c30339a91fa5078052ed1e
• https://git.kernel.org/stable/c/4b1761898861117c97066aea6c58f68a7787f0bf
• https://git.kernel.org/stable/c/64d17ec9f1ded042c4b188d15734f33486ed9966
• https://git.kernel.org/stable/c/6da24cfc83ba4f97ea44fc7ae9999a006101755c
• https://git.kernel.org/stable/c/ace300eecbccaa698e2b472843c74a5f33f7dce8
• https://git.kernel.org/stable/c/b7df21cf1b79ab7026f545e7bf837bd5750ac026