BUG: unable to handle kernel NULL pointer dereference in cipso_v4_sock_setattr

[Paul Moore]

On Tue, Feb 25, 2020 at 3:19 AM syzbot
<syzbot+f4dfece964792d80b139 at syzkaller.appspotmail.com> wrote:
>
> 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

Netdev folks, I'm not very familiar with the multipath TCP code so I
was wondering if you might help me out a bit with this report.  Based
on the stack trace above it looks like for a given AF_INET sock "sk",
inet_sk(sk)->is_icsk is true but inet_csk(sk) is NULL; should this be
possible under normal conditions or is there an issue somewhere?

-- 
paul moore
www.paul-moore.com