kernel NULL pointer dereference on selinux_ip_postroute

[Corentin Labbe]

Hello

since next-20211018 I got the following crash:
   56.084594] BUG: kernel NULL pointer dereference, address: 0000000000000290
[   56.092367] #PF: supervisor read access in kernel mode
[   56.097495] #PF: error_code(0x0000) - not-present page
[   56.102628] PGD 11ceb3067 P4D 11ceb3067 PUD 11ce68067 PMD 0 
[   56.108288] Oops: 0000 [#1] PREEMPT SMP NOPTI
[   56.112646] CPU: 0 PID: 171 Comm: dhcpcd Tainted: G         C        5.15.0-rc6-next-20211019+ #114
[   56.121684] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./K10N78, BIOS P2.00 07/01/2010
[   56.130978] RIP: 0010:selinux_ip_postroute_compat+0x4f/0x110
[   56.136645] Code: 7e 18 00 48 89 d7 f3 48 ab 0f 84 9b 00 00 00 48 8b 43 18 48 85 c0 74 0d 0f b6 48 12 80 f9 0c 0f 84 ad 00 00 00 48 89 54 24 10 <48> 8b a8 90 02 00 00 31 c9 31 d2 48 8b 46 10 4c 8d 44 24 07 48 89
[   56.155391] RSP: 0018:ffff9a5f4036f8f0 EFLAGS: 00010246
[   56.160615] RAX: 0000000000000000 RBX: ffff895d9cee8200 RCX: 0000000000000000
[   56.167740] RDX: ffff9a5f4036f918 RSI: ffff9a5f4036fa88 RDI: ffff9a5f4036f950
[   56.174865] RBP: ffff895d9cee8200 R08: ffff9a5f4036f9b8 R09: ffffffffb3a2d140
[   56.181987] R10: ffff895d9d2eb180 R11: ffff895d9cee8200 R12: ffff9a5f4036fa88
[   56.189113] R13: ffff895d9cee8200 R14: ffff9a5f4036fa88 R15: ffff895d80175218
[   56.196236] FS:  00007fe0b206a740(0000) GS:ffff895d9fc00000(0000) knlGS:0000000000000000
[   56.204314] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   56.210050] CR2: 0000000000000290 CR3: 000000011ceec000 CR4: 00000000000006f0
[   56.217175] Call Trace:
[   56.219622]  <TASK>
[   56.221728]  selinux_ip_postroute+0x177/0x440
[   56.226084]  ? selinux_ip_postroute+0x177/0x440
[   56.230616]  ? __ip6_append_data.isra.0+0xc38/0xff0
[   56.235496]  nf_hook_slow+0x3a/0xa0
[   56.238988]  ip6_finish_output2+0x56c/0x5f0
[   56.243167]  ? ip6_fragment+0x3d4/0x710
[   56.247005]  ? netif_rx_ni+0x100/0x100
[   56.250758]  ip6_send_skb+0x19/0x60
[   56.254243]  rawv6_sendmsg+0xc99/0xf90
[   56.257996]  ? __wake_up_common+0x74/0x140
[   56.262095]  ? sock_sendmsg+0x52/0x60
[   56.265761]  sock_sendmsg+0x52/0x60
[   56.269245]  ____sys_sendmsg+0x20c/0x260
[   56.273162]  ? sendmsg_copy_msghdr+0x74/0x90
[   56.277434]  ___sys_sendmsg+0x7c/0xc0
[   56.281094]  ? sock_read_iter+0x8d/0xf0
[   56.284932]  ? new_sync_read+0x185/0x1a0
[   56.288858]  __sys_sendmsg+0x54/0xa0
[   56.292436]  ? fpregs_assert_state_consistent+0x18/0x40
[   56.297663]  do_syscall_64+0x3b/0x90
[   56.301241]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[   56.306295] RIP: 0033:0x7fe0b2162163
[   56.309873] Code: 64 89 02 48 c7 c0 ff ff ff ff eb b7 66 2e 0f 1f 84 00 00 00 00 00 90 64 8b 04 25 18 00 00 00 85 c0 75 14 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 55 c3 0f 1f 40 00 48 83 ec 28 89 54 24 1c 48
[   56.328610] RSP: 002b:00007fffa63fa0e8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
[   56.336168] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007fe0b2162163
[   56.343291] RDX: 0000000000000000 RSI: 00007fffa640a248 RDI: 0000000000000006
[   56.350415] RBP: 00007fffa641a430 R08: 00007fffa640a280 R09: 00007fffa640a248
[   56.357540] R10: 0000000000000010 R11: 0000000000000246 R12: 0000000000000000
[   56.364663] R13: 00007fffa640a304 R14: 0000000000000020 R15: 0000000000000002
[   56.371789]  </TASK>
[   56.373973] Modules linked in: fc0013 it913x tea5767 tda8290 mxl5005s tda18218 mxl5007t tda18212 xc4000 tuner_xc2028 max2165 tea5761 m88rs6000t mt2060 e4000 mc44s803 qt1010 tuner_simple si2157 tuner_types fc0011 regmap_i2c iscsi_target_mod target_core_file target_core_mod configfs crct10dif_generic crc_t10dif crct10dif_common iptable_nat xt_addrtype nf_log_syslog xt_nat xt_LOG xt_mark xt_MASQUERADE adv7175 saa7110 zr36067(C) videobuf2_dma_contig
[   56.413371] CR2: 0000000000000290
[   56.416756] ---[ end trace ffe54c3f1e62823e ]---
[   56.422726] RIP: 0010:selinux_ip_postroute_compat+0x4f/0x110
[   56.429765] Code: 7e 18 00 48 89 d7 f3 48 ab 0f 84 9b 00 00 00 48 8b 43 18 48 85 c0 74 0d 0f b6 48 12 80 f9 0c 0f 84 ad 00 00 00 48 89 54 24 10 <48> 8b a8 90 02 00 00 31 c9 31 d2 48 8b 46 10 4c 8d 44 24 07 48 89
[   56.449899] RSP: 0018:ffff9a5f4036f8f0 EFLAGS: 00010246
[   56.456506] RAX: 0000000000000000 RBX: ffff895d9cee8200 RCX: 0000000000000000
[   56.465020] RDX: ffff9a5f4036f918 RSI: ffff9a5f4036fa88 RDI: ffff9a5f4036f950
[   56.473510] RBP: ffff895d9cee8200 R08: ffff9a5f4036f9b8 R09: ffffffffb3a2d140
[   56.482042] R10: ffff895d9d2eb180 R11: ffff895d9cee8200 R12: ffff9a5f4036fa88
[   56.489762] R13: ffff895d9cee8200 R14: ffff9a5f4036fa88 R15: ffff895d80175218
[   56.496896] FS:  00007fe0b206a740(0000) GS:ffff895d9fc00000(0000) knlGS:0000000000000000
[   56.504980] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   56.510728] CR2: 0000000000000290 CR3: 000000011ceec000 CR4: 00000000000006f0

Reverting 1d1e1ded1356 ("selinux: make better use of the nf_hook_state passed to the NF hooks") seems to remove this crash.

This is tested on a x86_64 board with x86_64_defconfig

Regards