Subject: Re: linux-next: manual merge of the userns tree with the vfs tree

From: Stephen Rothwell <[email-masked]>
Date: Mon, 6 Aug 2018 17:50:47 +1000

Hi all,

On Wed, 20 Jun 2018 12:39:05 +1000 Stephen Rothwell <[email-masked]> wrote:
>
> Today's linux-next merge of the userns tree got a conflict in:
> 
>   fs/proc/inode.c
>   fs/proc/root.c
> 
> between commit:
> 
>   0223e0999be2 ("procfs: Move proc_fill_super() to fs/proc/root.c")
>   83cd45075c36 ("proc: Add fs_context support to procfs")
> 
> from the vfs tree and commit:
> 
>   cc8cda3af2ba ("proc: Simplify and fix proc by removing the kernel mount")
>   9303f5f81bd4 ("proc: Change proc_parse_options to return an errno value")
>   04035aa33a12 ("proc: Don't change mount options on remount failure.")
> 
> from the userns tree.
> 
> I effectively reverted 9303f5f81bd4 and 04035aa33a12 since (I think)
> they are subsumed by the vfs tree changes.
> 
> I fixed it up (I think I got it mostly right this time - see below) and
> can carry the fix as necessary. This is now fixed as far as linux-next
> is concerned, but any non trivial conflicts should be mentioned to your
> upstream maintainer when your tree is submitted for merging.  You may
> also want to consider cooperating with the maintainer of the
> conflicting tree to minimise any particularly complex conflicts.
> 
> -- 
> Cheers,
> Stephen Rothwell
> 
> diff --cc fs/proc/root.c
> index efbdc08a3c86,3dceff6cd121..91e9b417bc6d
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@@ -80,71 -78,21 +80,74 @@@ static int proc_parse_option(struct fs_
>   	return 0;
>   }
>   
>  -int proc_remount(struct super_block *sb, int *flags, char *data)
>  +static void proc_set_options(struct super_block *s,
>  +			     struct fs_context *fc,
>  +			     struct pid_namespace *pid_ns,
>  +			     struct user_namespace *user_ns)
>   {
>  -	struct pid_namespace *pid = sb->s_fs_info;
>  -	struct proc_mount_options opts = {
>  -		.pid_gid  = pid->pid_gid,
>  -		.hide_pid = pid->hide_pid,
>  -	};
>  +	struct proc_fs_context *ctx = fc->fs_private;
>  +
>  +	if (ctx->mask & (1 << Opt_gid))
>  +		pid_ns->pid_gid = make_kgid(user_ns, ctx->gid);
>  +	if (ctx->mask & (1 << Opt_hidepid))
>  +		pid_ns->hide_pid = ctx->hidepid;
>  +}
>  +
>  +static int proc_fill_super(struct super_block *s, struct fs_context *fc)
>  +{
>  +	struct pid_namespace *pid_ns = get_pid_ns(s->s_fs_info);
>  +	struct inode *root_inode;
>   	int ret;
>   
>  -	sync_filesystem(sb);
>  -	ret = proc_parse_options(data, &opts);
>  -	if (ret)
>  +	proc_set_options(s, fc, pid_ns, current_user_ns());
>  +
>  +	/* User space would break if executables or devices appear on proc */
>  +	s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;
>  +	s->s_flags |= SB_NODIRATIME | SB_NOSUID | SB_NOEXEC;
>  +	s->s_blocksize = 1024;
>  +	s->s_blocksize_bits = 10;
>  +	s->s_magic = PROC_SUPER_MAGIC;
>  +	s->s_op = &proc_sops;
>  +	s->s_time_gran = 1;
>  +
>  +	/*
>  +	 * procfs isn't actually a stacking filesystem; however, there is
>  +	 * too much magic going on inside it to permit stacking things on
>  +	 * top of it
>  +	 */
>  +	s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
>  +
>  +	pde_get(&proc_root);
>  +	root_inode = proc_get_inode(s, &proc_root);
>  +	if (!root_inode) {
>  +		pr_err("proc_fill_super: get root inode failed\n");
>  +		return -ENOMEM;
>  +	}
>  +
>  +	s->s_root = d_make_root(root_inode);
>  +	if (!s->s_root) {
>  +		pr_err("proc_fill_super: allocate dentry failed\n");
>  +		return -ENOMEM;
>  +	}
>  +
>  +	ret = proc_setup_self(s);
>  +	if (ret) {
>   		return ret;
>  -	pid->pid_gid  = opts.pid_gid;
>  -	pid->hide_pid = opts.hide_pid;
>  +	}
> - 	return proc_setup_thread_self(s);
> ++	ret = proc_setup_thread_self(s);
> ++
> ++	rcu_assign_pointer(pid_ns->proc_super, s);
> ++	return ret;
>  +}
>  +
>  +int proc_reconfigure(struct super_block *sb, struct fs_context *fc)
>  +{
>  +	struct pid_namespace *pid = sb->s_fs_info;
>  +
>  +	sync_filesystem(sb);
>  +
>  +	if (fc)
>  +		proc_set_options(sb, fc, pid, current_user_ns());
>   	return 0;
>   }
>   
> @@@ -288,44 -208,23 +292,22 @@@ struct proc_dir_entry proc_root = 
>   	.proc_fops	= &proc_root_operations,
>   	.parent		= &proc_root,
>   	.subdir		= RB_ROOT,
>  -	.name		= proc_root.inline_name,
>  -	.inline_name	= "/proc",
>  +	.name		= "/proc",
>   };
>   
> - int pid_ns_prepare_proc(struct pid_namespace *ns)
> + #if defined(CONFIG_SYSCTL_SYSCALL) || defined(CONFIG_MCONSOLE)
> + struct file *file_open_proc(const char *pathname, int flags, umode_t mode)
>   {
> - 	struct proc_fs_context *ctx;
> - 	struct fs_context *fc;
>   	struct vfsmount *mnt;
> - 	int ret;
> - 
> - 	fc = vfs_new_fs_context(&proc_fs_type, NULL, 0,
> - 				FS_CONTEXT_FOR_KERNEL_MOUNT);
> - 	if (IS_ERR(fc))
> - 		return PTR_ERR(fc);
> - 
> - 	ctx = fc->fs_private;
> - 	if (ctx->pid_ns != ns) {
> - 		put_pid_ns(ctx->pid_ns);
> - 		get_pid_ns(ns);
> - 		ctx->pid_ns = ns;
> - 	}
> + 	struct file *file;
>   
> - 	ret = vfs_get_tree(fc);
> - 	if (ret < 0) {
> - 		put_fs_context(fc);
> - 		return ret;
> - 	}
> - 
> - 	mnt = vfs_create_mount(fc, 0);
> - 	put_fs_context(fc);
> + 	mnt = kern_mount(&proc_fs_type);
>   	if (IS_ERR(mnt))
> - 		return PTR_ERR(mnt);
> + 		return ERR_CAST(mnt);
>   
> - 	ns->proc_mnt = mnt;
> - 	return 0;
> - }
> + 	file = file_open_root(mnt->mnt_root, mnt, pathname, flags, mode);
> + 	kern_unmount(mnt);
>   
> - void pid_ns_release_proc(struct pid_namespace *ns)
> - {
> - 	kern_unmount(ns->proc_mnt);
> + 	return file;
>   }
> + #endif

Are there any comments on this resolution.  I just had to do it all
again due to slight changes in the vfs tree.  What are you guys going
to tell Linus when he comes to merge this?

-- 
Cheers,
Stephen Rothwell