linux-kernel - [PATCH 03/13] devpts: Cleanup newinstance parsing

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Date:	Mon,  4 Apr 2016 20:29:19 -0500
From:	"Eric W. Biederman" <ebiederm@...ssion.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Greg KH <greg@...ah.com>, Jiri Slaby <jslaby@...e.com>,
	Aurelien Jarno <aurelien@...el32.net>,
	Andy Lutomirski <luto@...capital.net>,
	Florian Weimer <fw@...eb.enyo.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Jann Horn <jann@...jh.net>,
	"security@...nel.org" <security@...nel.org>, security@...ntu.com,
	security@...ian.org, Willy Tarreau <w@....eu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 03/13] devpts: Cleanup newinstance parsing

Add a dedicated parsing routing for newinstance that does not modify
data, so parsing out newinstance can be separate from the parsing of
the other mount options.

Allways pass as data to parse_mount_options the filesystem specific
portion of the super_block that holds the mount options.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/devpts/inode.c | 44 ++++++++++++++++++++++----------------------
 1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 9f22c959d1f7..c3d53d2f7c3e 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -105,7 +105,6 @@ struct pts_mount_opts {
 	kgid_t   gid;
 	umode_t mode;
 	umode_t ptmxmode;
-	int newinstance;
 	int max;
 };
 
@@ -228,19 +227,27 @@ static inline struct super_block *pts_sb_from_inode(struct inode *inode)
 	return devpts_mnt->mnt_sb;
 }
 
-#define PARSE_MOUNT	0
-#define PARSE_REMOUNT	1
+static bool parse_newinstance(const char *data)
+{
+	while (data) {
+		const char *p = strchr(data, ',');
+		size_t len = p ? p - data : strlen(data);
+		if ((len == 11) && (memcmp(data, "newinstance", 11) == 0)) {
+			return true;
+		}
+		data = p ? p + 1 : NULL;
+	}
+	return false;
+}
 
 /*
  * parse_mount_options():
  *	Set @opts to mount options specified in @data. If an option is not
- *	specified in @data, set it to its default value. The exception is
- *	'newinstance' option which can only be set/cleared on a mount (i.e.
- *	cannot be changed during remount).
+ *	specified in @data, set it to its default value.
  *
  * Note: @data may be NULL (in which case all options are set to default).
  */
-static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
+static int parse_mount_options(char *data, struct pts_mount_opts *opts)
 {
 	char *p;
 	kuid_t uid;
@@ -254,10 +261,6 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
 	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 	opts->max     = NR_UNIX98_PTY_MAX;
 
-	/* newinstance makes sense only on initial mount */
-	if (op == PARSE_MOUNT)
-		opts->newinstance = 0;
-
 	while ((p = strsep(&data, ",")) != NULL) {
 		substring_t args[MAX_OPT_ARGS];
 		int token;
@@ -298,9 +301,6 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
 			opts->ptmxmode = option & S_IALLUGO;
 			break;
 		case Opt_newinstance:
-			/* newinstance makes sense only on initial mount */
-			if (op == PARSE_MOUNT)
-				opts->newinstance = 1;
 			break;
 		case Opt_max:
 			if (match_int(&args[0], &option) ||
@@ -399,7 +399,7 @@ static int devpts_remount(struct super_block *sb, int *flags, char *data)
 	struct pts_mount_opts *opts = &fsi->mount_opts;
 
 	sync_filesystem(sb);
-	err = parse_mount_options(data, PARSE_REMOUNT, opts);
+	err = parse_mount_options(data, opts);
 
 	/*
 	 * parse_mount_options() restores options to default values
@@ -528,20 +528,18 @@ static struct dentry *devpts_mount(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
 	int error;
-	struct pts_mount_opts opts;
 	struct super_block *s;
+	bool newinstance;
 
-	error = parse_mount_options(data, PARSE_MOUNT, &opts);
-	if (error)
-		return ERR_PTR(error);
+	newinstance = parse_newinstance(data);
 
 	/* Require newinstance for all user namespace mounts to ensure
 	 * the mount options are not changed.
 	 */
-	if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
+	if ((current_user_ns() != &init_user_ns) && !newinstance)
 		return ERR_PTR(-EINVAL);
 
-	if (opts.newinstance)
+	if (newinstance)
 		s = sget(fs_type, NULL, set_anon_super, flags, NULL);
 	else
 		s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
@@ -557,7 +555,9 @@ static struct dentry *devpts_mount(struct file_system_type *fs_type,
 		s->s_flags |= MS_ACTIVE;
 	}
 
-	memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
+	error = parse_mount_options(data, &DEVPTS_SB(s)->mount_opts);
+	if (error)
+		goto out_undo_sget;
 
 	error = mknod_ptmx(s);
 	if (error)
-- 
2.6.3