toracat / rpms / kernel

Forked from rpms/kernel 3 years ago
Clone

Blame SOURCES/centos-linux-3.10-0004-vfs-Lazily-remove-mounts-on-unlinked-files-and-direc.patch

b312fc
From 743848de574b660972f457c28c02cbb19c8aa439 Mon Sep 17 00:00:00 2001
b312fc
From: "T.kabe" <kabe@>
b312fc
Date: Fri, 3 Mar 2017 17:06:44 +0900
b312fc
Subject: [PATCH 4/4] vfs: Lazily remove mounts on unlinked files and directories.
b312fc
b312fc
[upstream commit 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe]
b312fc
[upstream commit 7af1364ffa64db61e386628594836e13d2ef04b5]
b312fc
b312fc
commit 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe
b312fc
Author: Eric W. Biederman <ebiederman@twitter.com>
b312fc
Date:   Tue Oct 1 18:33:48 2013 -0700
b312fc
b312fc
    vfs: Lazily remove mounts on unlinked files and directories.
b312fc
b312fc
    With the introduction of mount namespaces and bind mounts it became
b312fc
    possible to access files and directories that on some paths are mount
b312fc
    points but are not mount points on other paths.  It is very confusing
b312fc
    when rm -rf somedir returns -EBUSY simply because somedir is mounted
b312fc
    somewhere else.  With the addition of user namespaces allowing
b312fc
    unprivileged mounts this condition has gone from annoying to allowing
b312fc
    a DOS attack on other users in the system.
b312fc
b312fc
    The possibility for mischief is removed by updating the vfs to support
b312fc
    rename, unlink and rmdir on a dentry that is a mountpoint and by
b312fc
    lazily unmounting mountpoints on deleted dentries.
b312fc
b312fc
    In particular this change allows rename, unlink and rmdir system calls
b312fc
    on a dentry without a mountpoint in the current mount namespace to
b312fc
    succeed, and it allows rename, unlink, and rmdir performed on a
b312fc
    distributed filesystem to update the vfs cache even if when there is a
b312fc
    mount in some namespace on the original dentry.
b312fc
b312fc
    There are two common patterns of maintaining mounts: Mounts on trusted
b312fc
    paths with the parent directory of the mount point and all ancestory
b312fc
    directories up to / owned by root and modifiable only by root
b312fc
    (i.e. /media/xxx, /dev, /dev/pts, /proc, /sys, /sys/fs/cgroup/{cpu,
b312fc
    cpuacct, ...}, /usr, /usr/local).  Mounts on unprivileged directories
b312fc
    maintained by fusermount.
b312fc
b312fc
    In the case of mounts in trusted directories owned by root and
b312fc
    modifiable only by root the current parent directory permissions are
b312fc
    sufficient to ensure a mount point on a trusted path is not removed
b312fc
    or renamed by anyone other than root, even if there is a context
b312fc
    where the there are no mount points to prevent this.
b312fc
b312fc
    In the case of mounts in directories owned by less privileged users
b312fc
    races with users modifying the path of a mount point are already a
b312fc
    danger.  fusermount already uses a combination of chdir,
b312fc
    /proc/<pid>/fd/NNN, and UMOUNT_NOFOLLOW to prevent these races.  The
b312fc
    removable of global rename, unlink, and rmdir protection really adds
b312fc
    nothing new to consider only a widening of the attack window, and
b312fc
    fusermount is already safe against unprivileged users modifying the
b312fc
    directory simultaneously.
b312fc
b312fc
    In principle for perfect userspace programs returning -EBUSY for
b312fc
    unlink, rmdir, and rename of dentires that have mounts in the local
b312fc
    namespace is actually unnecessary.  Unfortunately not all userspace
b312fc
    programs are perfect so retaining -EBUSY for unlink, rmdir and rename
b312fc
    of dentries that have mounts in the current mount namespace plays an
b312fc
    important role of maintaining consistency with historical behavior and
b312fc
    making imperfect userspace applications hard to exploit.
b312fc
b312fc
    v2: Remove spurious old_dentry.
b312fc
    v3: Optimized shrink_submounts_and_drop
b312fc
        Removed unsued afs label
b312fc
    v4: Simplified the changes to check_submounts_and_drop
b312fc
        Do not rename check_submounts_and_drop shrink_submounts_and_drop
b312fc
        Document what why we need atomicity in check_submounts_and_drop
b312fc
        Rely on the parent inode mutex to make d_revalidate and d_invalidate
b312fc
        an atomic unit.
b312fc
    v5: Refcount the mountpoint to detach in case of simultaneous
b312fc
        renames.
b312fc
b312fc
    Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
b312fc
    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
b312fc
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
b312fc
b312fc
commit 7af1364ffa64db61e386628594836e13d2ef04b5
b312fc
Author: Eric W. Biederman <ebiederm@xmission.com>
b312fc
Date:   Fri Oct 4 19:15:13 2013 -0700
b312fc
b312fc
    vfs: Don't allow overwriting mounts in the current mount namespace
b312fc
b312fc
    In preparation for allowing mountpoints to be renamed and unlinked
b312fc
    in remote filesystems and in other mount namespaces test if on a dentry
b312fc
    there is a mount in the local mount namespace before allowing it to
b312fc
    be renamed or unlinked.
b312fc
b312fc
    The primary motivation here are old versions of fusermount unmount
b312fc
    which is not safe if the a path can be renamed or unlinked while it is
b312fc
    verifying the mount is safe to unmount.  More recent versions are simpler
b312fc
    and safer by simply using UMOUNT_NOFOLLOW when unmounting a mount
b312fc
    in a directory owned by an arbitrary user.
b312fc
b312fc
    Miklos Szeredi <miklos@szeredi.hu> reports this is approach is good
b312fc
    enough to remove concerns about new kernels mixed with old versions
b312fc
    of fusermount.
b312fc
b312fc
    A secondary motivation for restrictions here is that it removing empty
b312fc
    directories that have non-empty mount points on them appears to
b312fc
    violate the rule that rmdir can not remove empty directories.  As
b312fc
    Linus Torvalds pointed out this is useful for programs (like git) that
b312fc
    test if a directory is empty with rmdir.
b312fc
b312fc
    Therefore this patch arranges to enforce the existing mount point
b312fc
    semantics for local mount namespace.
b312fc
b312fc
    v2: Rewrote the test to be a drop in replacement for d_mountpoint
b312fc
    v3: Use bool instead of int as the return type of is_local_mountpoint
b312fc
b312fc
    Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
b312fc
    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
b312fc
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
b312fc
---
b312fc
 fs/dcache.c    | 69 +++++++++++++++++++++++++++++++---------------------------
b312fc
 fs/mount.h     |  9 ++++++++
b312fc
 fs/namei.c     | 16 +++++++++-----
b312fc
 fs/namespace.c | 35 +++++++++++++++++++++++++++++
b312fc
 4 files changed, 91 insertions(+), 38 deletions(-)
b312fc
b312fc
diff --git a/fs/dcache.c b/fs/dcache.c
b312fc
index 5dabe0e..a3e9e7a 100644
b312fc
--- a/fs/dcache.c
b312fc
+++ b/fs/dcache.c
b312fc
@@ -1285,36 +1285,38 @@ void shrink_dcache_parent(struct dentry *parent)
b312fc
 }
b312fc
 EXPORT_SYMBOL(shrink_dcache_parent);
b312fc
 
b312fc
-static enum d_walk_ret check_and_collect(void *_data, struct dentry *dentry)
b312fc
+struct detach_data {
b312fc
+	struct select_data select;
b312fc
+	struct dentry *mountpoint;
b312fc
+};
b312fc
+static enum d_walk_ret detach_and_collect(void *_data, struct dentry *dentry)
b312fc
 {
b312fc
-	struct select_data *data = _data;
b312fc
-
b312fc
-	if (d_mountpoint(dentry)) {
b312fc
-		data->found = -EBUSY;
b312fc
-		return D_WALK_QUIT;
b312fc
-	}
b312fc
+	struct detach_data *data = _data;
b312fc
 
b312fc
-	return select_collect(_data, dentry);
b312fc
-}
b312fc
+ 	if (d_mountpoint(dentry)) {
b312fc
+		__dget_dlock(dentry);
b312fc
+		data->mountpoint = dentry;
b312fc
+ 		return D_WALK_QUIT;
b312fc
+ 	}
b312fc
+	return select_collect(&data->select, dentry);
b312fc
+ }
b312fc
 
b312fc
 static void check_and_drop(void *_data)
b312fc
 {
b312fc
-	struct select_data *data = _data;
b312fc
+	struct detach_data *data = _data;
b312fc
 
b312fc
-	if (d_mountpoint(data->start))
b312fc
-		data->found = -EBUSY;
b312fc
-	if (!data->found)
b312fc
-		__d_drop(data->start);
b312fc
+	if (!data->mountpoint && !data->select.found)
b312fc
+		__d_drop(data->select.start);
b312fc
 }
b312fc
 
b312fc
 /**
b312fc
- * check_submounts_and_drop - prune dcache, check for submounts and drop
b312fc
+ * check_submounts_and_drop - detach submounts, prune dcache, and drop
b312fc
  *
b312fc
- * All done as a single atomic operation relative to has_unlinked_ancestor().
b312fc
- * Returns 0 if successfully unhashed @parent.  If there were submounts then
b312fc
- * return -EBUSY.
b312fc
+ * The final d_drop is done as an atomic operation relative to
b312fc
+ * rename_lock ensuring there are no races with d_set_mounted.  This
b312fc
+ * ensures there are no unhashed dentries on the path to a mountpoint.
b312fc
  *
b312fc
- * @dentry: dentry to prune and drop
b312fc
+ * @dentry: dentry to detach, prune and drop
b312fc
  */
b312fc
 int check_submounts_and_drop(struct dentry *dentry)
b312fc
 {
b312fc
@@ -1327,19 +1329,24 @@ int check_submounts_and_drop(struct dentry *dentry)
b312fc
 	}
b312fc
 
b312fc
 	for (;;) {
b312fc
-		struct select_data data;
b312fc
+		struct detach_data data;
b312fc
 
b312fc
-		INIT_LIST_HEAD(&data.dispose);
b312fc
-		data.start = dentry;
b312fc
-		data.found = 0;
b312fc
+		data.mountpoint = NULL;
b312fc
+		INIT_LIST_HEAD(&data.select.dispose);
b312fc
+		data.select.start = dentry;
b312fc
+		data.select.found = 0;
b312fc
 
b312fc
-		d_walk(dentry, &data, check_and_collect, check_and_drop);
b312fc
-		ret = data.found;
b312fc
+		d_walk(dentry, &data, detach_and_collect, check_and_drop);
b312fc
 
b312fc
-		if (!list_empty(&data.dispose))
b312fc
-			shrink_dentry_list(&data.dispose);
b312fc
+		if (data.select.found)
b312fc
+			shrink_dentry_list(&data.select.dispose);
b312fc
 
b312fc
-		if (ret <= 0)
b312fc
+		if (data.mountpoint) {
b312fc
+			detach_mounts(data.mountpoint);
b312fc
+			dput(data.mountpoint);
b312fc
+		}
b312fc
+
b312fc
+		if (!data.mountpoint && !data.select.found)
b312fc
 			break;
b312fc
 
b312fc
 		cond_resched();
b312fc
@@ -2554,10 +2561,8 @@ static struct dentry *__d_unalias(struct inode *inode,
b312fc
 		goto out_err;
b312fc
 	m2 = &alias->d_parent->d_inode->i_mutex;
b312fc
 out_unalias:
b312fc
-	if (likely(!d_mountpoint(alias))) {
b312fc
-		__d_move(alias, dentry, false);
b312fc
-		ret = alias;
b312fc
-	}
b312fc
+	__d_move(alias, dentry, false);
b312fc
+	ret = alias;
b312fc
 out_err:
b312fc
 	spin_unlock(&inode->i_lock);
b312fc
 	if (m2)
b312fc
diff --git a/fs/mount.h b/fs/mount.h
b312fc
index 9959119..a373c86 100644
b312fc
--- a/fs/mount.h
b312fc
+++ b/fs/mount.h
b312fc
@@ -107,3 +107,12 @@ struct proc_mounts {
b312fc
 #define proc_mounts(p) (container_of((p), struct proc_mounts, m))
b312fc
 
b312fc
 extern const struct seq_operations mounts_op;
b312fc
+
b312fc
+extern bool __is_local_mountpoint(struct dentry *dentry);
b312fc
+static inline bool is_local_mountpoint(struct dentry *dentry)
b312fc
+{
b312fc
+	if (!d_mountpoint(dentry))
b312fc
+		return false;
b312fc
+
b312fc
+	return __is_local_mountpoint(dentry);
b312fc
+}
b312fc
diff --git a/fs/namei.c b/fs/namei.c
b312fc
index 872e5e5..ef70aa8 100644
b312fc
--- a/fs/namei.c
b312fc
+++ b/fs/namei.c
b312fc
@@ -3691,8 +3691,8 @@ int vfs_rmdir(struct inode *dir, struct dentry *dentry)
b312fc
 	mutex_lock(&dentry->d_inode->i_mutex);
b312fc
 
b312fc
 	error = -EBUSY;
b312fc
-	if (d_mountpoint(dentry))
b312fc
-		goto out;
b312fc
+ 	if (is_local_mountpoint(dentry))
b312fc
+ 		goto out;
b312fc
 
b312fc
 	error = security_inode_rmdir(dir, dentry);
b312fc
 	if (error)
b312fc
@@ -3705,6 +3705,7 @@ int vfs_rmdir(struct inode *dir, struct dentry *dentry)
b312fc
 
b312fc
 	dentry->d_inode->i_flags |= S_DEAD;
b312fc
 	dont_mount(dentry);
b312fc
+	detach_mounts(dentry);
b312fc
 
b312fc
 out:
b312fc
 	mutex_unlock(&dentry->d_inode->i_mutex);
b312fc
@@ -3806,7 +3807,7 @@ int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegate
b312fc
 		return -EPERM;
b312fc
 
b312fc
 	mutex_lock(&target->i_mutex);
b312fc
-	if (d_mountpoint(dentry))
b312fc
+	if (is_local_mountpoint(dentry))
b312fc
 		error = -EBUSY;
b312fc
 	else {
b312fc
 		error = security_inode_unlink(dir, dentry);
b312fc
@@ -3815,8 +3816,10 @@ int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegate
b312fc
 			if (error)
b312fc
 				goto out;
b312fc
 			error = dir->i_op->unlink(dir, dentry);
b312fc
-			if (!error)
b312fc
+			if (!error) {
b312fc
 				dont_mount(dentry);
b312fc
+				detach_mounts(dentry);
b312fc
+			}
b312fc
 		}
b312fc
 	}
b312fc
 out:
b312fc
@@ -4254,8 +4257,8 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
b312fc
 		mutex_lock(&target->i_mutex);
b312fc
 
b312fc
 	error = -EBUSY;
b312fc
-	if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry))
b312fc
-		goto out;
b312fc
+ 	if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry))
b312fc
+ 		goto out;
b312fc
 
b312fc
 	if (max_links && new_dir != old_dir) {
b312fc
 		error = -EMLINK;
b312fc
@@ -4292,6 +4295,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
b312fc
 		if (is_dir)
b312fc
 			target->i_flags |= S_DEAD;
b312fc
 		dont_mount(new_dentry);
b312fc
+		detach_mounts(new_dentry);
b312fc
 	}
b312fc
 	if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) {
b312fc
 		if (!(flags & RENAME_EXCHANGE))
b312fc
diff --git a/fs/namespace.c b/fs/namespace.c
b312fc
index e48fed3..d633562 100644
b312fc
--- a/fs/namespace.c
b312fc
+++ b/fs/namespace.c
b312fc
@@ -625,6 +625,41 @@ static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
b312fc
 	return NULL;
b312fc
 }
b312fc
 
b312fc
+/*
b312fc
+ * __is_local_mountpoint - Test to see if dentry is a mountpoint in the
b312fc
+ *                         current mount namespace.
b312fc
+ *
b312fc
+ * The common case is dentries are not mountpoints at all and that
b312fc
+ * test is handled inline.  For the slow case when we are actually
b312fc
+ * dealing with a mountpoint of some kind, walk through all of the
b312fc
+ * mounts in the current mount namespace and test to see if the dentry
b312fc
+ * is a mountpoint.
b312fc
+ *
b312fc
+ * The mount_hashtable is not usable in the context because we
b312fc
+ * need to identify all mounts that may be in the current mount
b312fc
+ * namespace not just a mount that happens to have some specified
b312fc
+ * parent mount.
b312fc
+ */
b312fc
+bool __is_local_mountpoint(struct dentry *dentry)
b312fc
+{
b312fc
+	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
b312fc
+	struct mount *mnt;
b312fc
+	bool is_covered = false;
b312fc
+
b312fc
+	if (!d_mountpoint(dentry))
b312fc
+		goto out;
b312fc
+
b312fc
+	down_read(&namespace_sem);
b312fc
+	list_for_each_entry(mnt, &ns->list, mnt_list) {
b312fc
+		is_covered = (mnt->mnt_mountpoint == dentry);
b312fc
+		if (is_covered)
b312fc
+			break;
b312fc
+	}
b312fc
+	up_read(&namespace_sem);
b312fc
+out:
b312fc
+	return is_covered;
b312fc
+}
b312fc
+
b312fc
 static struct mountpoint *new_mountpoint(struct dentry *dentry)
b312fc
 {
b312fc
 	struct list_head *chain = mountpoint_hashtable + hash(NULL, dentry);
b312fc
-- 
b312fc
1.8.3.1
b312fc