Use After Free Affecting kernel-debuginfo package, versions <0:4.14.238-182.421.amzn2
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Test your applications- Snyk IDSNYK-AMZN2-KERNELDEBUGINFO-7919033
- published6 Sept 2024
- disclosed25 Mar 2024
Introduced: 25 Mar 2024
CVE-2021-47162 (opens in a new tab)How to fix?
Upgrade Amazon-Linux:2 kernel-debuginfo to version 0:4.14.238-182.421.amzn2 or higher.
This issue was patched in ALAS2-2021-1685.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-debuginfo package and not the kernel-debuginfo package as distributed by Amazon-Linux.
See How to fix? for Amazon-Linux:2 relevant fixed versions and status.
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.
References
- http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-47162
- https://git.kernel.org/stable/c/436d650d374329a591c30339a91fa5078052ed1e
- https://git.kernel.org/stable/c/4b1761898861117c97066aea6c58f68a7787f0bf
- https://git.kernel.org/stable/c/5489f30bb78ff0dafb4229a69632afc2ba20765c
- 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/b2c8d28c34b3070407cb1741f9ba3f15d0284b8b
- https://git.kernel.org/stable/c/b7df21cf1b79ab7026f545e7bf837bd5750ac026