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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <5c6f3d62-4cec-2aea-4693-62928611c526@gmail.com> References: <5c6f3d62-4cec-2aea-4693-62928611c526@gmail.com> <153754740781.17872.7869536526927736855.stgit@warthog.procyon.org.uk> <153754743491.17872.12115848333103740766.stgit@warthog.procyon.org.uk> <862e36a2-2a6f-4e26-3228-8cab4b4cf230@gmail.com> To: Alan Jenkins , viro@zeniv.linux.org.uk Cc: dhowells@redhat.com, torvalds@linux-foundation.org, ebiederm@xmission.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, mszeredi@redhat.com Subject: Re: [PATCH 03/34] teach move_mount(2) to work with OPEN_TREE_CLONE [ver #12] MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <17404.1539272035.1@warthog.procyon.org.uk> Content-Transfer-Encoding: 8BIT Date: Thu, 11 Oct 2018 16:33:55 +0100 Message-ID: <17405.1539272035@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 11 Oct 2018 15:33:58 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Okay, this appears to fix the cycle-creation problem. It could probably be improved by comparing sequence numbers as Alan suggests, but I need to work out how to get at that. David --- commit 069c3376f7849044117c866aeafbb1a525f84926 Author: David Howells Date: Thu Oct 4 23:18:59 2018 +0100 fixes diff --git a/fs/internal.h b/fs/internal.h index 17029b30e196..47a6c80c3c51 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -172,6 +172,7 @@ extern void mnt_pin_kill(struct mount *m); * fs/nsfs.c */ extern const struct dentry_operations ns_dentry_operations; +extern struct file_system_type nsfs; /* * fs/ioctl.c diff --git a/fs/namespace.c b/fs/namespace.c index e969ded7d54b..25ecd8b3c76b 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2388,6 +2388,27 @@ static inline int tree_contains_unbindable(struct mount *mnt) return 0; } +/* + * Object if there are any nsfs mounts in the specified subtree. These can act + * as pins for mount namespaces that aren't checked by the mount-cycle checking + * code, thereby allowing cycles to be made. + */ +static bool check_for_nsfs_mounts(struct mount *subtree) +{ + struct mount *p; + bool ret = false; + + lock_mount_hash(); + for (p = subtree; p; p = next_mnt(p, subtree)) + if (p->mnt.mnt_sb->s_type == &nsfs) + goto out; + + ret = true; +out: + unlock_mount_hash(); + return ret; +} + static int do_move_mount(struct path *old_path, struct path *new_path) { struct path parent_path = {.mnt = NULL, .dentry = NULL}; @@ -2442,6 +2463,8 @@ static int do_move_mount(struct path *old_path, struct path *new_path) if (IS_MNT_SHARED(p) && tree_contains_unbindable(old)) goto out1; err = -ELOOP; + if (!check_for_nsfs_mounts(old)) + goto out1; for (; mnt_has_parent(p); p = p->mnt_parent) if (p == old) goto out1; diff --git a/fs/nsfs.c b/fs/nsfs.c index f069eb6495b0..d3abcd5c2a23 100644 --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -269,7 +269,7 @@ static struct dentry *nsfs_mount(struct file_system_type *fs_type, return mount_pseudo(fs_type, "nsfs:", &nsfs_ops, &ns_dentry_operations, NSFS_MAGIC); } -static struct file_system_type nsfs = { +struct file_system_type nsfs = { .name = "nsfs", .mount = nsfs_mount, .kill_sb = kill_anon_super,