BUG: unable to handle kernel NULL pointer dereference in cipso_v4_sock_setattr

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    ca7e1fd1 Merge tag 'linux-kselftest-5.6-rc3' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=179f0931e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a61f2164c515c07f
dashboard link: https://syzkaller.appspot.com/bug?extid=f4dfece964792d80b139
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14fdfdede00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17667de9e00000

The bug was bisected to:

commit 2303f994b3e187091fd08148066688b08f837efc
Author: Peter Krystad <peter.krystad at linux.intel.com>
Date:   Wed Jan 22 00:56:17 2020 +0000

    mptcp: Associate MPTCP context with TCP socket

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14fbec81e00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=16fbec81e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=12fbec81e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f4dfece964792d80b139 at syzkaller.appspotmail.com
Fixes: 2303f994b3e1 ("mptcp: Associate MPTCP context with TCP socket")

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 8e171067 P4D 8e171067 PUD 93fa2067 PMD 0 
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 8984 Comm: syz-executor066 Not tainted 5.6.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:0x0
Code: Bad RIP value.
RSP: 0018:ffffc900020b7b80 EFLAGS: 00010246
RAX: 1ffff110124ba600 RBX: 0000000000000000 RCX: ffff88809fefa600
RDX: ffff8880994cdb18 RSI: 0000000000000000 RDI: ffff8880925d3140
RBP: ffffc900020b7bd8 R08: ffffffff870225be R09: fffffbfff140652a
R10: fffffbfff140652a R11: 0000000000000000 R12: ffff8880925d35d0
R13: ffff8880925d3140 R14: dffffc0000000000 R15: 1ffff110124ba6ba
FS:  0000000001a0b880(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000000a6d6f000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 cipso_v4_sock_setattr+0x34b/0x470 net/ipv4/cipso_ipv4.c:1888
 netlbl_sock_setattr+0x2a7/0x310 net/netlabel/netlabel_kapi.c:989
 smack_netlabel security/smack/smack_lsm.c:2425 [inline]
 smack_inode_setsecurity+0x3da/0x4a0 security/smack/smack_lsm.c:2716
 security_inode_setsecurity+0xb2/0x140 security/security.c:1364
 __vfs_setxattr_noperm+0x16f/0x3e0 fs/xattr.c:197
 vfs_setxattr fs/xattr.c:224 [inline]
 setxattr+0x335/0x430 fs/xattr.c:451
 __do_sys_fsetxattr fs/xattr.c:506 [inline]
 __se_sys_fsetxattr+0x130/0x1b0 fs/xattr.c:495
 __x64_sys_fsetxattr+0xbf/0xd0 fs/xattr.c:495
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440199
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffcadc19e48 EFLAGS: 00000246 ORIG_RAX: 00000000000000be
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440199
RDX: 0000000020000200 RSI: 00000000200001c0 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000003 R09: 00000000004002c8
R10: 0000000000000009 R11: 0000000000000246 R12: 0000000000401a20
R13: 0000000000401ab0 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
CR2: 0000000000000000
---[ end trace 9bbc7bb8e1061a42 ]---
RIP: 0010:0x0
Code: Bad RIP value.
RSP: 0018:ffffc900020b7b80 EFLAGS: 00010246
RAX: 1ffff110124ba600 RBX: 0000000000000000 RCX: ffff88809fefa600
RDX: ffff8880994cdb18 RSI: 0000000000000000 RDI: ffff8880925d3140
RBP: ffffc900020b7bd8 R08: ffffffff870225be R09: fffffbfff140652a
R10: fffffbfff140652a R11: 0000000000000000 R12: ffff8880925d35d0
R13: ffff8880925d3140 R14: dffffc0000000000 R15: 1ffff110124ba6ba
FS:  0000000001a0b880(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000000a6d6f000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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