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Date:	Mon, 6 Oct 2014 23:30:07 +0400
From:	Andrey Wagin <avagin@...il.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: BUG at /build/buildd/linux-3.13.0/fs/pnode.c:372!

2014-10-06 22:19 GMT+04:00 Serge E. Hallyn <serge@...lyn.com>:
> Quoting Andrey Wagin (avagin@...il.com):
>> Hi All,
>>
>> Here is a small program, which triggers a bug. Is it interested for someone?
>
> Yup, would
>
> diff --git a/fs/namespace.c b/fs/namespace.c
> index ef42d9b..ddef25d 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -3046,6 +3046,9 @@ static int mntns_install(struct nsproxy *nsproxy, void *ns)
>         struct mnt_namespace *mnt_ns = ns;
>         struct path root;
>
> +       if (mnt_ns == nsproxy->mnt_ns)
> +               return 0;
> +
>         if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
>             !ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
>             !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
>
> fix it?

Actually the bug is triggered from the second umount. I think we need
something like this:
diff --git a/fs/namespace.c b/fs/namespace.c
index 68685b2..bbcd92c 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1363,6 +1363,9 @@ static int do_umount(struct mount *mnt, int flags)
                return retval;
        }

+       if (mnt->mnt_parent == mnt)
+               return -EINVAL;
+
        namespace_lock();
        lock_mount_hash();
        event++;

root@...ntu:/home/avagin# strace ./a.out
...
open("/proc/self/ns/mnt", O_RDONLY)     = 3
umount("/", MNT_DETACH)                 = 0
setns(3, 131072)                        = 0
umount("/", MNT_DETACH)                 = -1 EINVAL (Invalid argument)
exit_group(0)                           = ?
+++ exited with 0 +++

>
>> root@...ntu:/home/avagin# cat nsenter.c
>> #define _GNU_SOURCE             /* See feature_test_macros(7) */
>> #include <sched.h>
>> #include <sys/types.h>
>> #include <sys/stat.h>
>> #include <fcntl.h>
>> #include <unistd.h>
>> #include <sys/mount.h>
>>
>> int main(int argc, char **argv)
>> {
>>         int fd;
>>
>>         fd = open("/proc/self/ns/mnt", O_RDONLY);
>>         if (fd < 0)
>>                 return 1;
>>         umount2("/", MNT_DETACH);
>>         if (setns(fd, CLONE_NEWNS))
>>                 return 1;
>>         umount2("/", MNT_DETACH);
>>
>>         return 0;
>> }
>>
>> root@...ntu:/home/avagin# gcc nsenter.c -o nsenter
>> root@...ntu:/home/avagin# ./nsenter
>>
>>
>> [  260.548301] ------------[ cut here ]------------
>> [  260.550941] kernel BUG at /build/buildd/linux-3.13.0/fs/pnode.c:372!
>> [  260.552068] invalid opcode: 0000 [#1] SMP
>> [  260.552068] Modules linked in: xt_CHECKSUM iptable_mangle xt_tcpudp
>> xt_addrtype xt_conntrack ipt_MASQUERADE iptable_nat nf_conntrack_ipv4
>> nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack bridge stp llc
>> dm_thin_pool dm_persistent_data dm_bufio dm_bio_prison iptable_filter
>> ip_tables x_tables crct10dif_pclmul crc32_pclmul ghash_clmulni_intel
>> binfmt_misc nfsd auth_rpcgss nfs_acl aesni_intel nfs lockd aes_x86_64
>> sunrpc fscache lrw gf128mul glue_helper ablk_helper cryptd serio_raw
>> ppdev parport_pc lp parport btrfs xor raid6_pq libcrc32c psmouse
>> floppy
>> [  260.552068] CPU: 0 PID: 1723 Comm: nsenter Not tainted
>> 3.13.0-30-generic #55-Ubuntu
>> [  260.552068] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
>> [  260.552068] task: ffff8800376097f0 ti: ffff880074824000 task.ti:
>> ffff880074824000
>> [  260.552068] RIP: 0010:[<ffffffff811e9483>]  [<ffffffff811e9483>]
>> propagate_umount+0x123/0x130
>> [  260.552068] RSP: 0018:ffff880074825e98  EFLAGS: 00010246
>> [  260.552068] RAX: ffff88007c741140 RBX: 0000000000000002 RCX: ffff88007c741190
>> [  260.552068] RDX: ffff88007c741190 RSI: ffff880074825ec0 RDI: ffff880074825ec0
>> [  260.552068] RBP: ffff880074825eb0 R08: 00000000000172e0 R09: ffff88007fc172e0
>> [  260.552068] R10: ffffffff811cc642 R11: ffffea0001d59000 R12: ffff88007c741140
>> [  260.552068] R13: ffff88007c741140 R14: ffff88007c741140 R15: 0000000000000000
>> [  260.552068] FS:  00007fd5c7e41740(0000) GS:ffff88007fc00000(0000)
>> knlGS:0000000000000000
>> [  260.552068] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [  260.552068] CR2: 00007fd5c7968050 CR3: 0000000070124000 CR4: 00000000000406f0
>> [  260.552068] Stack:
>> [  260.552068]  0000000000000002 0000000000000002 ffff88007c631000
>> ffff880074825ed8
>> [  260.552068]  ffffffff811dcfac ffff88007c741140 0000000000000002
>> ffff88007c741160
>> [  260.552068]  ffff880074825f38 ffffffff811dd12b ffffffff811cc642
>> 0000000075640000
>> [  260.552068] Call Trace:
>> [  260.552068]  [<ffffffff811dcfac>] umount_tree+0x20c/0x260
>> [  260.552068]  [<ffffffff811dd12b>] do_umount+0x12b/0x300
>> [  260.552068]  [<ffffffff811cc642>] ? final_putname+0x22/0x50
>> [  260.552068]  [<ffffffff811cc849>] ? putname+0x29/0x40
>> [  260.552068]  [<ffffffff811dd88c>] SyS_umount+0xdc/0x100
>> [  260.552068]  [<ffffffff8172aeff>] tracesys+0xe1/0xe6
>> [  260.552068] Code: 89 50 08 48 8b 50 08 48 89 02 49 89 45 08 e9 72
>> ff ff ff 0f 1f 44 00 00 4c 89 e6 4c 89 e7 e8 f5 f6 ff ff 48 89 c3 e9
>> 39 ff ff ff <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 90 66 66 66 66 90 55
>> b8 01
>> [  260.552068] RIP  [<ffffffff811e9483>] propagate_umount+0x123/0x130
>> [  260.552068]  RSP <ffff880074825e98>
>> [  260.611451] ---[ end trace 11c33d85f1d4c652 ]---
>> --
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