From eff0c5c06eb119d7ddc397928fd26228ad436fc0 Mon Sep 17 00:00:00 2001
From: Alistair Strachan <astrachan@google.com>
Date: Wed, 6 Jun 2018 13:46:44 -0700
Subject: [PATCH] Revert "proc: Convert proc_mount to use mount_ns."

This reverts commit e94591d0d90c13166cb6eb54ce5f96ed13d81b55.

This cleanup broke the parsing of procfs mount parameters.

Bug: 79705088
Change-Id: I0f07180ef9a994c884abfa269ffb273ee0bcbc0d
Signed-off-by: Alistair Strachan <astrachan@google.com>
---
 fs/proc/inode.c    |  9 ++------
 fs/proc/internal.h |  3 +--
 fs/proc/root.c     | 52 ++++++++++++++++++++++++++++++++++++++++++----
 3 files changed, 51 insertions(+), 13 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 225f541f7078..c5f154be0ab2 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -472,17 +472,12 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
 	return inode;
 }
 
-int proc_fill_super(struct super_block *s, void *data, int silent)
+int proc_fill_super(struct super_block *s)
 {
-	struct pid_namespace *ns = get_pid_ns(s->s_fs_info);
 	struct inode *root_inode;
 	int ret;
 
-	if (!proc_parse_options(data, ns))
-		return -EINVAL;
-
-	/* 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_iflags |= SB_I_USERNS_VISIBLE | SB_I_NODEV;
 	s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;
 	s->s_blocksize = 1024;
 	s->s_blocksize_bits = 10;
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 5e55186858c9..02e0d9e9b3fe 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -203,7 +203,7 @@ extern const struct inode_operations proc_pid_link_inode_operations;
 extern void proc_init_inodecache(void);
 void set_proc_pid_nlink(void);
 extern struct inode *proc_get_inode(struct super_block *, struct proc_dir_entry *);
-extern int proc_fill_super(struct super_block *, void *data, int flags);
+extern int proc_fill_super(struct super_block *);
 extern void proc_entry_rundown(struct proc_dir_entry *);
 
 /*
@@ -270,7 +270,6 @@ static inline void proc_tty_init(void) {}
  * root.c
  */
 extern struct proc_dir_entry proc_root;
-extern int proc_parse_options(char *options, struct pid_namespace *pid);
 
 extern void proc_self_init(void);
 extern int proc_remount(struct super_block *, int *, char *);
diff --git a/fs/proc/root.c b/fs/proc/root.c
index eafe87e010ec..ef6840c64e95 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -26,6 +26,21 @@
 
 #include "internal.h"
 
+static int proc_test_super(struct super_block *sb, void *data)
+{
+	return sb->s_fs_info == data;
+}
+
+static int proc_set_super(struct super_block *sb, void *data)
+{
+	int err = set_anon_super(sb, NULL);
+	if (!err) {
+		struct pid_namespace *ns = (struct pid_namespace *)data;
+		sb->s_fs_info = get_pid_ns(ns);
+	}
+	return err;
+}
+
 enum {
 	Opt_gid, Opt_hidepid, Opt_err,
 };
@@ -36,7 +51,7 @@ static const match_table_t tokens = {
 	{Opt_err, NULL},
 };
 
-int proc_parse_options(char *options, struct pid_namespace *pid)
+static int proc_parse_options(char *options, struct pid_namespace *pid)
 {
 	char *p;
 	substring_t args[MAX_OPT_ARGS];
@@ -89,16 +104,45 @@ int proc_remount(struct super_block *sb, int *flags, char *data)
 static struct dentry *proc_mount(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
+	int err;
+	struct super_block *sb;
 	struct pid_namespace *ns;
+	char *options;
 
 	if (flags & MS_KERNMOUNT) {
-		ns = data;
-		data = NULL;
+		ns = (struct pid_namespace *)data;
+		options = NULL;
 	} else {
 		ns = task_active_pid_ns(current);
+		options = data;
+
+		/* Does the mounter have privilege over the pid namespace? */
+		if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
+			return ERR_PTR(-EPERM);
+	}
+
+	sb = sget(fs_type, proc_test_super, proc_set_super, flags, ns);
+	if (IS_ERR(sb))
+		return ERR_CAST(sb);
+
+	if (!proc_parse_options(options, ns)) {
+		deactivate_locked_super(sb);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (!sb->s_root) {
+		err = proc_fill_super(sb);
+		if (err) {
+			deactivate_locked_super(sb);
+			return ERR_PTR(err);
+		}
+
+		sb->s_flags |= MS_ACTIVE;
+		/* User space would break if executables appear on proc */
+		sb->s_iflags |= SB_I_NOEXEC;
 	}
 
-	return mount_ns(fs_type, flags, data, ns, ns->user_ns, proc_fill_super);
+	return dget(sb->s_root);
 }
 
 static void proc_kill_sb(struct super_block *sb)
-- 
2.20.1