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Date:	Mon, 6 Oct 2014 23:50:57 +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 23:44 GMT+04:00 Serge E. Hallyn <serge@...lyn.com>:
> Quoting Andrey Wagin (avagin@...il.com):
>> 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
>
> Oh, I see.
>
>> 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)
>
> looks good (or the equivalent  mnt_has_parent(mnt)).  Have you tested that
> this prevents your test program from causing a crash?

Yes, I have. Look the strace output below. Today here is too late for
sending a proper patch.

>
>> +               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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