CVE-2021-47103

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