Re: linux-next boot error: general protection fault in do_mount_root

[Eric Biggers]

On Mon, Dec 16, 2019 at 08:45:08AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    cf2be78b Add linux-next specific files for 20191216
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13f505dee00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=634b7ce01f79423d
> dashboard link: https://syzkaller.appspot.com/bug?extid=31f37c1dc3fd9e900602
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+31f37c1dc3fd9e900602@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> batman_adv: B.A.T.M.A.N. advanced 2019.5 (compatibility version 15) loaded
> openvswitch: Open vSwitch switching datapath
> NET: Registered protocol family 40
> mpls_gso: MPLS GSO support
> IPI shorthand broadcast: enabled
> AVX2 version of gcm_enc/dec engaged.
> AES CTR mode by8 optimization enabled
> sched_clock: Marking stable (12282186706, 24150593)->(12316857222,
> -10519923)
> registered taskstats version 1
> Loading compiled-in X.509 certificates
> Loaded X.509 cert 'Build time autogenerated kernel key:
> 8b22f477d966bfa6cf9a482acbda6ca1892a4acc'
> zswap: loaded using pool lzo/zbud
> Key type ._fscrypt registered
> Key type .fscrypt registered
> Btrfs loaded, crc32c=crc32c-intel
> Key type big_key registered
> Key type encrypted registered
> AppArmor: AppArmor sha1 policy hashing enabled
> ima: No TPM chip found, activating TPM-bypass!
> ima: Allocated hash algorithm: sha256
> ima: No architecture policies found
> evm: Initialising EVM extended attributes:
> evm: security.selinux
> evm: security.SMACK64
> evm: security.SMACK64EXEC
> evm: security.SMACK64TRANSMUTE
> evm: security.SMACK64MMAP
> evm: security.apparmor
> evm: security.ima
> evm: security.capability
> evm: HMAC attrs: 0x1
> PM:   Magic number: 15:311:439
> media media3: hash matches
> printk: console [netcon0] enabled
> netconsole: network logging started
> gtp: GTP module loaded (pdp ctx size 104 bytes)
> rdma_rxe: loaded
> cfg80211: Loading compiled-in X.509 certificates for regulatory database
> cfg80211: Loaded X.509 cert 'sforshee: 00b28ddf47aef9cea7'
> ALSA device list:
>   #0: Dummy 1
>   #1: Loopback 1
>   #2: Virtual MIDI Card 1
> md: Waiting for all devices to be available before autodetect
> md: If you don't use raid, use raid=noautodetect
> md: Autodetecting RAID arrays.
> md: autorun ...
> md: ... autorun DONE.
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.5.0-rc2-next-20191216-syzkaller
> #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:strncpy+0x35/0xc0 lib/string.c:119
> Code: e5 41 56 41 55 4c 8d 34 17 49 bd 00 00 00 00 00 fc ff df 41 54 53 48
> 89 fb 48 83 ec 10 48 89 f2 48 89 f1 48 c1 ea 03 83 e1 07 <42> 0f b6 14 2a 38
> ca 7f 04 84 d2 75 40 48 89 da 48 89 d9 44 0f b6
> RSP: 0000:ffffc90000c7fca8 EFLAGS: 00010246
> RAX: ffff888099090000 RBX: ffff888099090000 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff888099090000
> RBP: ffffc90000c7fcd8 R08: ffff888099090000 R09: ffffed1015d07074
> R10: ffffed1015d07073 R11: ffff8880ae83839b R12: ffffea0002642400
> R13: dffffc0000000000 R14: ffff888099090fff R15: ffff888214cc3000
> FS:  0000000000000000(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000000 CR3: 000000000986d000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  strncpy include/linux/string.h:326 [inline]
>  do_mount_root+0x74/0x23b init/do_mounts.c:404
>  mount_block_root+0x342/0x51a init/do_mounts.c:438
>  mount_root+0x283/0x2cd init/do_mounts.c:628
>  prepare_namespace+0x26f/0x2a7 init/do_mounts.c:687
>  kernel_init_freeable+0x557/0x570 init/main.c:1233
>  kernel_init+0x12/0x1bf init/main.c:1112
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> Modules linked in:
> ---[ end trace c645a4d31f27fe8a ]---
> RIP: 0010:strncpy+0x35/0xc0 lib/string.c:119
> Code: e5 41 56 41 55 4c 8d 34 17 49 bd 00 00 00 00 00 fc ff df 41 54 53 48
> 89 fb 48 83 ec 10 48 89 f2 48 89 f1 48 c1 ea 03 83 e1 07 <42> 0f b6 14 2a 38
> ca 7f 04 84 d2 75 40 48 89 da 48 89 d9 44 0f b6
> RSP: 0000:ffffc90000c7fca8 EFLAGS: 00010246
> RAX: ffff888099090000 RBX: ffff888099090000 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff888099090000
> RBP: ffffc90000c7fcd8 R08: ffff888099090000 R09: ffffed1015d07074
> R10: ffffed1015d07073 R11: ffff8880ae83839b R12: ffffea0002642400
> R13: dffffc0000000000 R14: ffff888099090fff R15: ffff888214cc3000
> FS:  0000000000000000(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000000 CR3: 000000000986d000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
> 
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 

Fixed in mainline by commit 7de7de7ca0ae0

#syz fix: Fix root mounting with no mount options

- Eric