CVE-2021-47162

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.