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From:   Miklos Szeredi <mszeredi@redhat.com>
To:     David Howells <dhowells@redhat.com>
Cc:     Al Viro <viro@ZenIV.linux.org.uk>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH 3/6] mount: fix regression in setting "subtype" from legacy API
Date:   Thu, 20 Sep 2018 17:12:11 +0200
Message-Id: <20180920151214.15484-4-mszeredi@redhat.com>
In-Reply-To: <20180920151214.15484-1-mszeredi@redhat.com>
References: <20180920151214.15484-1-mszeredi@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Subtype was initilized at the wrong place from the wrong source
(fstype->fs_type->name, which does not ever contain a subtype).

Set subtype from do_new_mount(), where it actually does something.
Verified with fuse.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/fs_context.c | 34 ----------------------------------
 fs/namespace.c  | 21 +++++++++++++++++++++
 2 files changed, 21 insertions(+), 34 deletions(-)

diff --git a/fs/fs_context.c b/fs/fs_context.c
index ceaf42559016..c0ecbb1ecdfe 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -684,27 +684,6 @@ static int legacy_validate(struct fs_context *fc)
 				     ctx->secdata);
 }
 
-/*
- * Determine the superblock subtype.
- */
-static int legacy_set_subtype(struct fs_context *fc)
-{
-	const char *subtype = strchr(fc->fs_type->name, '.');
-
-	if (subtype) {
-		subtype++;
-		if (!subtype[0])
-			return -EINVAL;
-	} else {
-		subtype = "";
-	}
-
-	fc->subtype = kstrdup(subtype, GFP_KERNEL);
-	if (!fc->subtype)
-		return -ENOMEM;
-	return 0;
-}
-
 /*
  * Get a mountable root with the legacy mount command.
  */
@@ -713,7 +692,6 @@ static int legacy_get_tree(struct fs_context *fc)
 	struct legacy_fs_context *ctx = fc->fs_private;
 	struct super_block *sb;
 	struct dentry *root;
-	int ret;
 
 	root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
 				      fc->source, ctx->legacy_data,
@@ -724,20 +702,8 @@ static int legacy_get_tree(struct fs_context *fc)
 	sb = root->d_sb;
 	BUG_ON(!sb);
 
-	if ((fc->fs_type->fs_flags & FS_HAS_SUBTYPE) &&
-	    !fc->subtype) {
-		ret = legacy_set_subtype(fc);
-		if (ret < 0)
-			goto err_sb;
-	}
-
 	fc->root = root;
 	return 0;
-
-err_sb:
-	dput(root);
-	deactivate_locked_super(sb);
-	return ret;
 }
 
 /*
diff --git a/fs/namespace.c b/fs/namespace.c
index 865b6f2c5e7d..7671c1f6fc22 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2617,6 +2617,7 @@ static int do_new_mount(struct path *mountpoint, const char *fstype,
 {
 	struct file_system_type *fs_type;
 	struct fs_context *fc;
+	const char *subtype = NULL;
 	int err;
 
 	if (!fstype)
@@ -2627,6 +2628,19 @@ static int do_new_mount(struct path *mountpoint, const char *fstype,
 	if (!fs_type)
 		goto out;
 
+	if (fs_type->fs_flags & FS_HAS_SUBTYPE) {
+		subtype = strchr(fstype, '.');
+		if (subtype) {
+			subtype++;
+			if (!subtype[0]) {
+				put_filesystem(fs_type);
+				return -EINVAL;
+			}
+		} else {
+			subtype = "";
+		}
+	}
+
 	fc = vfs_new_fs_context(fs_type, NULL, sb_flags, sb_flags,
 				FS_CONTEXT_FOR_USER_MOUNT);
 	put_filesystem(fs_type);
@@ -2635,6 +2649,13 @@ static int do_new_mount(struct path *mountpoint, const char *fstype,
 		goto out;
 	}
 
+	if (subtype) {
+		fc->subtype = kstrdup(subtype, GFP_KERNEL);
+		err = -ENOMEM;
+		if (!fc->subtype)
+			goto out;
+	}
+
 	if (name) {
 		err = vfs_parse_fs_string(fc, "source", name, strlen(name));
 		if (err < 0)
-- 
2.14.3