From ec2aa8e8dd7d35524a68c89b9e7ceb07fb002561 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Mon, 20 Aug 2012 17:28:58 -0700 Subject: userns: Allow the userns root to mount of devpts - The context in which devpts is mounted has no effect on the creation of ptys as the /dev/ptmx interface has been used by unprivileged users for many years. - Only support unprivileged mounts in combination with the newinstance option to ensure that mounting of /dev/pts in a user namespace will not allow the options of an existing mount of devpts to be modified. - Create /dev/pts/ptmx as the root user in the user namespace that mounts devpts so that it's permissions to be changed. Acked-by: Serge Hallyn Signed-off-by: "Eric W. Biederman" --- fs/devpts/inode.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'fs') diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c index 472e6befc54d..073d30b9d1ac 100644 --- a/fs/devpts/inode.c +++ b/fs/devpts/inode.c @@ -243,6 +243,13 @@ static int mknod_ptmx(struct super_block *sb) struct dentry *root = sb->s_root; struct pts_fs_info *fsi = DEVPTS_SB(sb); struct pts_mount_opts *opts = &fsi->mount_opts; + kuid_t root_uid; + kgid_t root_gid; + + root_uid = make_kuid(current_user_ns(), 0); + root_gid = make_kgid(current_user_ns(), 0); + if (!uid_valid(root_uid) || !gid_valid(root_gid)) + return -EINVAL; mutex_lock(&root->d_inode->i_mutex); @@ -273,6 +280,8 @@ static int mknod_ptmx(struct super_block *sb) mode = S_IFCHR|opts->ptmxmode; init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2)); + inode->i_uid = root_uid; + inode->i_gid = root_gid; d_add(dentry, inode); @@ -438,6 +447,12 @@ static struct dentry *devpts_mount(struct file_system_type *fs_type, if (error) return ERR_PTR(error); + /* Require newinstance for all user namespace mounts to ensure + * the mount options are not changed. + */ + if ((current_user_ns() != &init_user_ns) && !opts.newinstance) + return ERR_PTR(-EINVAL); + if (opts.newinstance) s = sget(fs_type, NULL, set_anon_super, flags, NULL); else @@ -491,6 +506,9 @@ static struct file_system_type devpts_fs_type = { .name = "devpts", .mount = devpts_mount, .kill_sb = devpts_kill_sb, +#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES + .fs_flags = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT, +#endif }; /* -- cgit v1.2.3-58-ga151