Re: [PATCH net-next v2 3/5] udp_tunnel: fix UaF in GRO accounting

[Sabrina Dubroca <sd@queasysnail.net>]

2025-03-21, 12:52:54 +0100, Paolo Abeni wrote:
> Siyzkaller reported a race in UDP tunnel GRO accounting, leading to
> UaF:
> 
> BUG: KASAN: slab-use-after-free in udp_tunnel_update_gro_lookup+0x23c/0x2c0 net/ipv4/udp_offload.c:65
> Read of size 8 at addr ffff88801235ebe8 by task syz.2.655/7921
> 
> CPU: 1 UID: 0 PID: 7921 Comm: syz.2.655 Not tainted 6.14.0-rc6-syzkaller-01313-g23c9ff659140 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>  print_address_description mm/kasan/report.c:408 [inline]
>  print_report+0x16e/0x5b0 mm/kasan/report.c:521
>  kasan_report+0x143/0x180 mm/kasan/report.c:634
>  udp_tunnel_update_gro_lookup+0x23c/0x2c0 net/ipv4/udp_offload.c:65
>  sk_common_release+0x71/0x2e0 net/core/sock.c:3896
>  inet_release+0x17d/0x200 net/ipv4/af_inet.c:435
>  __sock_release net/socket.c:647 [inline]
>  sock_release+0x82/0x150 net/socket.c:675
>  sock_free drivers/net/wireguard/socket.c:339 [inline]
>  wg_socket_reinit+0x215/0x380 drivers/net/wireguard/socket.c:435
>  wg_stop+0x59f/0x600 drivers/net/wireguard/device.c:133
>  __dev_close_many+0x3a6/0x700 net/core/dev.c:1717
>  dev_close_many+0x24e/0x4c0 net/core/dev.c:1742
>  unregister_netdevice_many_notify+0x629/0x24f0 net/core/dev.c:11923
>  rtnl_delete_link net/core/rtnetlink.c:3512 [inline]
>  rtnl_dellink+0x526/0x8c0 net/core/rtnetlink.c:3554
>  rtnetlink_rcv_msg+0x791/0xcf0 net/core/rtnetlink.c:6945
>  netlink_rcv_skb+0x206/0x480 net/netlink/af_netlink.c:2534
>  netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
>  netlink_unicast+0x7f6/0x990 net/netlink/af_netlink.c:1339
>  netlink_sendmsg+0x8de/0xcb0 net/netlink/af_netlink.c:1883
>  sock_sendmsg_nosec net/socket.c:709 [inline]
>  __sock_sendmsg+0x221/0x270 net/socket.c:724
>  ____sys_sendmsg+0x53a/0x860 net/socket.c:2564
>  ___sys_sendmsg net/socket.c:2618 [inline]
>  __sys_sendmsg+0x269/0x350 net/socket.c:2650
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f35ab38d169
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f35ac28f038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007f35ab5a6160 RCX: 00007f35ab38d169
> RDX: 0000000000000000 RSI: 0000400000000000 RDI: 0000000000000004
> RBP: 00007f35ab40e2a0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000001 R14: 00007f35ab5a6160 R15: 00007ffdddd781b8
>  </TASK>
> 
> Allocated by task 7770:
>  kasan_save_stack mm/kasan/common.c:47 [inline]
>  kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
>  unpoison_slab_object mm/kasan/common.c:319 [inline]
>  __kasan_slab_alloc+0x66/0x80 mm/kasan/common.c:345
>  kasan_slab_alloc include/linux/kasan.h:250 [inline]
>  slab_post_alloc_hook mm/slub.c:4115 [inline]
>  slab_alloc_node mm/slub.c:4164 [inline]
>  kmem_cache_alloc_noprof+0x1d9/0x380 mm/slub.c:4171
>  sk_prot_alloc+0x58/0x210 net/core/sock.c:2190
>  sk_alloc+0x3e/0x370 net/core/sock.c:2249
>  inet_create+0x648/0xea0 net/ipv4/af_inet.c:326
>  __sock_create+0x4c0/0xa30 net/socket.c:1539
>  sock_create net/socket.c:1597 [inline]
>  __sys_socket_create net/socket.c:1634 [inline]
>  __sys_socket+0x150/0x3c0 net/socket.c:1681
>  __do_sys_socket net/socket.c:1695 [inline]
>  __se_sys_socket net/socket.c:1693 [inline]
>  __x64_sys_socket+0x7a/0x90 net/socket.c:1693
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Freed by task 7768:
>  kasan_save_stack mm/kasan/common.c:47 [inline]
>  kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
>  kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:576
>  poison_slab_object mm/kasan/common.c:247 [inline]
>  __kasan_slab_free+0x59/0x70 mm/kasan/common.c:264
>  kasan_slab_free include/linux/kasan.h:233 [inline]
>  slab_free_hook mm/slub.c:2353 [inline]
>  slab_free mm/slub.c:4609 [inline]
>  kmem_cache_free+0x195/0x410 mm/slub.c:4711
>  sk_prot_free net/core/sock.c:2230 [inline]
>  __sk_destruct+0x4fd/0x690 net/core/sock.c:2327
>  inet_release+0x17d/0x200 net/ipv4/af_inet.c:435
>  __sock_release net/socket.c:647 [inline]
>  sock_close+0xbc/0x240 net/socket.c:1389
>  __fput+0x3e9/0x9f0 fs/file_table.c:464
>  task_work_run+0x24f/0x310 kernel/task_work.c:227
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
>  exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
>  syscall_exit_to_user_mode+0x13f/0x340 kernel/entry/common.c:218
>  do_syscall_64+0x100/0x230 arch/x86/entry/common.c:89
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> The buggy address belongs to the object at ffff88801235e4c0
>  which belongs to the cache UDP of size 1856
> The buggy address is located 1832 bytes inside of
>  freed 1856-byte region [ffff88801235e4c0, ffff88801235ec00)
> 
> At disposal time, to avoid unconditionally acquiring a spin lock, UDP
> tunnel sockets are conditionally removed from the known tunnels list
> only if the socket is actually present in such a list.
> 
> Such check happens outside the socket lock scope: the current CPU
> could observe an uninitialized list entry even if the tunnel has been
> actually registered by a different core.
> 
> Address the issue moving the blamed check under the relevant list
> spin lock.
> 
> Reported-by: syzbot+1fb3291cc1beeb3c315a@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=1fb3291cc1beeb3c315a
> Fixes: 8d4880db37835 ("udp_tunnel: create a fastpath GRO lookup.")
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>

-- 
Sabrina