Commit 8654df4e authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

mnt: Refactor fs_fully_visible into mount_too_revealing 



Replace the call of fs_fully_visible in do_new_mount from before the
new superblock is allocated with a call of mount_too_revealing after
the superblock is allocated.   This winds up being a much better location
for maintainability of the code.

The first change this enables is the replacement of FS_USERNS_VISIBLE
with SB_I_USERNS_VISIBLE.  Moving the flag from struct filesystem_type
to sb_iflags on the superblock.

Unfortunately mount_too_revealing fundamentally needs to touch
mnt_flags adding several MNT_LOCKED_XXX flags at the appropriate
times.  If the mnt_flags did not need to be touched the code
could be easily moved into the filesystem specific mount code.

Acked-by: default avatarSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 695e9df0

fs/namespace.c

+25 −13
Original line number Diff line number Diff line
@@ -2375,7 +2375,7 @@ unlock: 
	return err;

}



static bool fs_fully_visible(struct file_system_type *fs_type, int *new_mnt_flags);

static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);



/*

 * create a new mount for userspace and request it to be added into the
@@ -2408,12 +2408,6 @@ static int do_new_mount(struct path *path, const char *fstype, int flags, 
			flags |= MS_NODEV;

			mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;

		}

		if (type->fs_flags & FS_USERNS_VISIBLE) {

			if (!fs_fully_visible(type, &mnt_flags)) {

				put_filesystem(type);

				return -EPERM;

			}

		}

	}



	mnt = vfs_kern_mount(type, flags, name, data);
@@ -2425,6 +2419,11 @@ static int do_new_mount(struct path *path, const char *fstype, int flags, 
	if (IS_ERR(mnt))

		return PTR_ERR(mnt);



	if (mount_too_revealing(mnt, &mnt_flags)) {

		mntput(mnt);

		return -EPERM;

	}



	err = do_add_mount(real_mount(mnt), path, mnt_flags);

	if (err)

		mntput(mnt);
@@ -3216,22 +3215,19 @@ bool current_chrooted(void) 
	return chrooted;

}



static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)

static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,

				int *new_mnt_flags)

{

	struct mnt_namespace *ns = current->nsproxy->mnt_ns;

	int new_flags = *new_mnt_flags;

	struct mount *mnt;

	bool visible = false;



	if (unlikely(!ns))

		return false;



	down_read(&namespace_sem);

	list_for_each_entry(mnt, &ns->list, mnt_list) {

		struct mount *child;

		int mnt_flags;



		if (mnt->mnt.mnt_sb->s_type != type)

		if (mnt->mnt.mnt_sb->s_type != new->mnt_sb->s_type)

			continue;



		/* This mount is not fully visible if it's root directory
@@ -3298,6 +3294,22 @@ found: 
	return visible;

}



static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)

{

	struct mnt_namespace *ns = current->nsproxy->mnt_ns;

	unsigned long s_iflags;



	if (ns->user_ns == &init_user_ns)

		return false;



	/* Can this filesystem be too revealing? */

	s_iflags = mnt->mnt_sb->s_iflags;

	if (!(s_iflags & SB_I_USERNS_VISIBLE))

		return false;



	return !mnt_already_visible(ns, mnt, new_mnt_flags);

}



static struct ns_common *mntns_get(struct task_struct *task)

{

	struct ns_common *ns = NULL;

fs/proc/inode.c

+1 −0
Original line number Diff line number Diff line
@@ -462,6 +462,7 @@ int proc_fill_super(struct super_block *s) 
	struct inode *root_inode;

	int ret;



	s->s_iflags |= SB_I_USERNS_VISIBLE;

	s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;

	s->s_blocksize = 1024;

	s->s_blocksize_bits = 10;

fs/proc/root.c

+1 −1
Original line number Diff line number Diff line
@@ -158,7 +158,7 @@ static struct file_system_type proc_fs_type = { 
	.name		= "proc",

	.mount		= proc_mount,

	.kill_sb	= proc_kill_sb,

	.fs_flags	= FS_USERNS_VISIBLE | FS_USERNS_MOUNT,

	.fs_flags	= FS_USERNS_MOUNT,

};



void __init proc_root_init(void)

fs/sysfs/mount.c

+2 −2
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type, 
		kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);

	else if (new_sb)

		/* Userspace would break if executables appear on sysfs */

		root->d_sb->s_iflags |= SB_I_NOEXEC;

		root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC;



	return root;

}
@@ -59,7 +59,7 @@ static struct file_system_type sysfs_fs_type = { 
	.name		= "sysfs",

	.mount		= sysfs_mount,

	.kill_sb	= sysfs_kill_sb,

	.fs_flags	= FS_USERNS_VISIBLE | FS_USERNS_MOUNT,

	.fs_flags	= FS_USERNS_MOUNT,

};



int __init sysfs_init(void)

include/linux/fs.h

+3 −1
Original line number Diff line number Diff line
@@ -1328,6 +1328,9 @@ struct mm_struct; 
#define SB_I_CGROUPWB	0x00000001	/* cgroup-aware writeback enabled */

#define SB_I_NOEXEC	0x00000002	/* Ignore executables on this fs */



/* sb->s_iflags to limit user namespace mounts */

#define SB_I_USERNS_VISIBLE		0x00000010 /* fstype already mounted */



/* Possible states of 'frozen' field */

enum {

	SB_UNFROZEN = 0,		/* FS is unfrozen */
@@ -2011,7 +2014,6 @@ struct file_system_type { 
#define FS_HAS_SUBTYPE		4

#define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */

#define FS_USERNS_DEV_MOUNT	16 /* A userns mount does not imply MNT_NODEV */

#define FS_USERNS_VISIBLE	32	/* FS must already be visible */

#define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */

	struct dentry *(*mount) (struct file_system_type *, int,

		       const char *, void *);

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