linux-kernel - [PATCH 03/11] vfs: Don't allow overwriting mounts in the current mount namespace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Sat, 15 Feb 2014 13:36:38 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Rob Landley <rob@...dley.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Christoph Hellwig <hch@...radead.org>,
	Karel Zak <kzak@...hat.com>,
	"J. Bruce Fields" <bfields@...ldses.org>
Subject: [PATCH 03/11] vfs: Don't allow overwriting mounts in the current mount namespace


In preparation for allowing mountpoints to be renamed and unlinked
in remote filesystems and in other mount namespaces test if on a dentry
there is a mount in the local mount namespace before allowing it to
be renamed or unlinked.

The primary motivation here are old versions of fusermount unmount
which is not safe if the a path can be renamed or unlinked while it is
verifying the mount is safe to unmount.  More recent versions are simpler
and safer by simply using UMOUNT_NOFOLLOW when unmounting a mount
in a directory owned by an arbitrary user.

Miklos Szeredi <miklos@...redi.hu> reports this is approach is good
enough to remove concerns about new kernels mixed with old versions
of fusermount.

A secondary motivation for restrictions here is that it removing empty
directories that have non-empty mount points on them appears to
violate the rule that rmdir can not remove empty directories.  As
Linus Torvalds pointed out this is useful for programs (like git) that
test if a directory is empty with rmdir.

Therefore this patch arranges to enforce the existing mount point
semantics for local mount namespace.

v2: Rewrote the test to be a drop in replacement for d_mountpoint

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/mount.h     |    9 +++++++++
 fs/namei.c     |    8 +++++++-
 fs/namespace.c |   35 +++++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 1 deletions(-)

diff --git a/fs/mount.h b/fs/mount.h
index a17458ca6f29..17d913d86add 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -109,3 +109,12 @@ struct proc_mounts {
 #define proc_mounts(p) (container_of((p), struct proc_mounts, m))
 
 extern const struct seq_operations mounts_op;
+
+extern int __is_local_mountpoint(struct dentry *dentry);
+static inline int is_local_mountpoint(struct dentry *dentry)
+{
+	if (!d_mountpoint(dentry))
+		return 0;
+
+	return __is_local_mountpoint(dentry);
+}
diff --git a/fs/namei.c b/fs/namei.c
index d580df2e6804..4e6fe16ef488 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3507,6 +3507,8 @@ int vfs_rmdir(struct inode *dir, struct dentry *dentry)
 	mutex_lock(&dentry->d_inode->i_mutex);
 
 	error = -EBUSY;
+	if (is_local_mountpoint(dentry))
+		goto out;
 	if (d_mountpoint(dentry))
 		goto out;
 
@@ -3622,7 +3624,7 @@ int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegate
 		return -EPERM;
 
 	mutex_lock(&target->i_mutex);
-	if (d_mountpoint(dentry))
+	if (is_local_mountpoint(dentry) || d_mountpoint(dentry))
 		error = -EBUSY;
 	else {
 		error = security_inode_unlink(dir, dentry);
@@ -4001,6 +4003,8 @@ static int vfs_rename_dir(struct inode *old_dir, struct dentry *old_dentry,
 		mutex_lock(&target->i_mutex);
 
 	error = -EBUSY;
+	if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry))
+		goto out;
 	if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry))
 		goto out;
 
@@ -4045,6 +4049,8 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
 	lock_two_nondirectories(source, target);
 
 	error = -EBUSY;
+	if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry))
+		goto out;
 	if (d_mountpoint(old_dentry)||d_mountpoint(new_dentry))
 		goto out;
 
diff --git a/fs/namespace.c b/fs/namespace.c
index 22e536705c45..6dc23614d44d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -631,6 +631,41 @@ struct vfsmount *lookup_mnt(struct path *path)
 	return m;
 }
 
+/*
+ * __is_local_mountpoint - Test to see if dentry is a mountpoint in the
+ *                         current mount namespace.
+ *
+ * The common case is dentries are not mountpoints at all and that
+ * test is handled inline.  For the slow case when we are actually
+ * dealing with a mountpoint of some kind, walk through all of the
+ * mounts in the current mount namespace and test to see if the dentry
+ * is a mountpoint.
+ *
+ * The mount_hashtable is not usable in the context because we
+ * need to identify all mounts that may be in the current mount
+ * namespace not just a mount that happens to have some specified
+ * parent mount.
+ */
+int __is_local_mountpoint(struct dentry *dentry)
+{
+	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
+	struct mount *mnt;
+	int is_covered = 0;
+
+	if (!d_mountpoint(dentry))
+		goto out;
+
+	down_read(&namespace_sem);
+	list_for_each_entry(mnt, &ns->list, mnt_list) {
+		is_covered = (mnt->mnt_mountpoint == dentry);
+		if (is_covered)
+			break;
+	}
+	up_read(&namespace_sem);
+out:
+	return is_covered;
+}
+
 static struct mountpoint *new_mountpoint(struct dentry *dentry)
 {
 	struct list_head *chain = mountpoint_hashtable + hash(NULL, dentry);
-- 
1.7.5.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/