CVE-2021-47103

In the Linux kernel, the following vulnerability has been resolved: inet:
fully convert sk->sk_rx_dst to RCU rules syzbot reported various issues
around early demux, one being included in this changelog [1] sk->sk_rx_dst
is using RCU protection without clearly documenting it. And following
sequences in tcp_v4_do_rcv()/tcp_v6_do_rcv() are not following standard RCU
rules. [a] dst_release(dst); [b] sk->sk_rx_dst = NULL; They look wrong
because a delete operation of RCU protected pointer is supposed to clear
the pointer before the call_rcu()/synchronize_rcu() guarding actual memory
freeing. In some cases indeed, dst could be freed before [b] is done. We
could cheat by clearing sk_rx_dst before calling dst_release(), but this
seems the right time to stick to standard RCU annotations and debugging
facilities. [1] BUG: KASAN: use-after-free in dst_check
include/net/dst.h:470 [inline] BUG: KASAN: use-after-free in
tcp_v4_early_demux+0x95b/0x960 net/ipv4/tcp_ipv4.c:1792 Read of size 2 at
addr ffff88807f1cb73a by task syz-executor.5/9204 CPU: 0 PID: 9204 Comm:
syz-executor.5 Not tainted 5.16.0-rc5-syzkaller #0 Hardware name: Google
Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call
Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_address_description.constprop.0.cold+0x8d/0x320 mm/kasan/report.c:247
__kasan_report mm/kasan/report.c:433 [inline] kasan_report.cold+0x83/0xdf
mm/kasan/report.c:450 dst_check include/net/dst.h:470 [inline]
tcp_v4_early_demux+0x95b/0x960 net/ipv4/tcp_ipv4.c:1792
ip_rcv_finish_core.constprop.0+0x15de/0x1e80 net/ipv4/ip_input.c:340
ip_list_rcv_finish.constprop.0+0x1b2/0x6e0 net/ipv4/ip_input.c:583
ip_sublist_rcv net/ipv4/ip_input.c:609 [inline] ip_list_rcv+0x34e/0x490
net/ipv4/ip_input.c:644 __netif_receive_skb_list_ptype net/core/dev.c:5508
[inline] __netif_receive_skb_list_core+0x549/0x8e0 net/core/dev.c:5556
__netif_receive_skb_list net/core/dev.c:5608 [inline]
netif_receive_skb_list_internal+0x75e/0xd80 net/core/dev.c:5699
gro_normal_list net/core/dev.c:5853 [inline] gro_normal_list
net/core/dev.c:5849 [inline] napi_complete_done+0x1f1/0x880
net/core/dev.c:6590 virtqueue_napi_complete drivers/net/virtio_net.c:339
[inline] virtnet_poll+0xca2/0x11b0 drivers/net/virtio_net.c:1557
__napi_poll+0xaf/0x440 net/core/dev.c:7023 napi_poll net/core/dev.c:7090
[inline] net_rx_action+0x801/0xb40 net/core/dev.c:7177
__do_softirq+0x29b/0x9c2 kernel/softirq.c:558 invoke_softirq
kernel/softirq.c:432 [inline] __irq_exit_rcu+0x123/0x180
kernel/softirq.c:637 irq_exit_rcu+0x5/0x20 kernel/softirq.c:649
common_interrupt+0x52/0xc0 arch/x86/kernel/irq.c:240
asm_common_interrupt+0x1e/0x40 arch/x86/include/asm/idtentry.h:629 RIP:
0033:0x7f5e972bfd57 Code: 39 d1 73 14 0f 1f 80 00 00 00 00 48 8b 50 f8 48
83 e8 08 48 39 ca 77 f3 48 39 c3 73 3e 48 89 13 48 8b 50 f8 48 89 38 49 8b
0e <48> 8b 3e 48 83 c3 08 48 83 c6 08 eb bc 48 39 d1 72 9e 48 39 d0 73 RSP:
002b:00007fff8a413210 EFLAGS: 00000283 RAX: 00007f5e97108990 RBX:
00007f5e97108338 RCX: ffffffff81d3aa45 RDX: ffffffff81d3aa45 RSI:
00007f5e97108340 RDI: ffffffff81d3aa45 RBP: 00007f5e97107eb8 R08:
00007f5e97108d88 R09: 0000000093c2e8d9 R10: 0000000000000000 R11:
0000000000000000 R12: 00007f5e97107eb0 R13: 00007f5e97108338 R14:
00007f5e97107ea8 R15: 0000000000000019 </TASK> Allocated by task 13:
kasan_save_stack+0x1e/0x50 mm/kasan/common.c:38 kasan_set_track
mm/kasan/common.c:46 [inline] set_alloc_info mm/kasan/common.c:434 [inline]
__kasan_slab_alloc+0x90/0xc0 mm/kasan/common.c:467 kasan_slab_alloc
include/linux/kasan.h:259 [inline] slab_post_alloc_hook mm/slab.h:519
[inline] slab_alloc_node mm/slub.c:3234 [inline] slab_alloc mm/slub.c:3242
[inline] kmem_cache_alloc+0x202/0x3a0 mm/slub.c:3247 dst_alloc+0x146/0x1f0
net/core/dst.c:92 rt_dst_alloc+0x73/0x430 net/ipv4/route.c:1613
ip_route_input_slow+0x1817/0x3a20 net/ipv4/route.c:234 —truncated—