Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753506AbaJGTxO (ORCPT ); Tue, 7 Oct 2014 15:53:14 -0400 Received: from relay.parallels.com ([195.214.232.42]:60727 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750895AbaJGTxL (ORCPT ); Tue, 7 Oct 2014 15:53:11 -0400 Date: Tue, 7 Oct 2014 23:53:07 +0400 From: Andrew Vagin To: "Eric W. Biederman" CC: Al Viro , Andrey Vagin , , , Serge Hallyn Subject: Re: [PATCH] umount: Do not allow unmounting rootfs. Message-ID: <20141007195307.GA23694@paralelels.com> References: <1412683212-28077-1-git-send-email-avagin@openvz.org> <20141007132431.GF7996@ZenIV.linux.org.uk> <20141007134011.GA569@paralelels.com> <87vbnv3cl1.fsf_-_@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset="koi8-r" Content-Disposition: inline In-Reply-To: <87vbnv3cl1.fsf_-_@x220.int.ebiederm.org> User-Agent: Mutt/1.5.23 (2014-03-12) X-Originating-IP: [10.24.24.25] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 07, 2014 at 12:27:06PM -0700, Eric W. Biederman wrote: > > Andrew Vagin writes: > > > #define _GNU_SOURCE > > #include > > #include > > #include > > #include > > #include > > #include > > > > int main(int argc, char **argv) > > { > > int fd; > > > > fd = open("/proc/self/ns/mnt", O_RDONLY); > > if (fd < 0) > > return 1; > > while (1) { > > if (umount2("/", MNT_DETACH) || > > setns(fd, CLONE_NEWNS)) > > break; > > } > > > > return 0; > > } > > > > root@ubuntu:/home/avagin# gcc -Wall nsenter.c -o nsenter > > root@ubuntu:/home/avagin# strace ./nsenter > > execve("./nsenter", ["./nsenter"], [/* 22 vars */]) = 0 > > ... > > open("/proc/self/ns/mnt", O_RDONLY) = 3 > > umount("/", MNT_DETACH) = 0 > > setns(3, 131072) = 0 > > umount("/", MNT_DETACH > > > causes: > > > [ 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:[] [] 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] [] umount_tree+0x20c/0x260 > > [ 260.552068] [] do_umount+0x12b/0x300 > > [ 260.552068] [] ? final_putname+0x22/0x50 > > [ 260.552068] [] ? putname+0x29/0x40 > > [ 260.552068] [] SyS_umount+0xdc/0x100 > > [ 260.552068] [] 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 [] propagate_umount+0x123/0x130 > > [ 260.552068] RSP > > [ 260.611451] ---[ end trace 11c33d85f1d4c652 ]-- > > Which in practice is totally uninteresting. Only the global root user can > do it, and it is just a stupid thing to do. > > However that is no excuse to allow a silly way to oops the kernel. > > We can avoid this silly problem by setting MNT_LOCKED on the rootfs > mount point and thus avoid needing any special cases in the unmount > code. I had this idea too, but it doesn't work. MNT_LOCKED isn't inherited, if the privileged user creates a new mount namespace. So "unshame -m ./nsenter" reproduces the same BUG. Thanks, Andrey > > Signed-off-by: "Eric W. Biederman" > --- > fs/namespace.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/fs/namespace.c b/fs/namespace.c > index 7c5834381a73..9c6ee037bef7 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -2887,6 +2887,7 @@ static void __init init_mount_tree(void) > > root.mnt = mnt; > root.dentry = mnt->mnt_root; > + mnt->mnt_flags |= MNT_LOCKED; > > set_fs_pwd(current->fs, &root); > set_fs_root(current->fs, &root); > -- > 1.9.1 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/