linux-kernel - [PATCH 4.8 114/140] isofs: Do not return EACCES for unknown filesystems

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Date:   Wed, 26 Oct 2016 14:22:54 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...il.com>,
        Karel Zak <kzak@...hat.com>, Jan Kara <jack@...e.cz>
Subject: [PATCH 4.8 114/140] isofs: Do not return EACCES for unknown filesystems

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@...e.cz>

commit a2ed0b391dd9c3ef1d64c7c3e370f4a5ffcd324a upstream.

When isofs_mount() is called to mount a device read-write, it returns
EACCES even before it checks that the device actually contains an isofs
filesystem. This may confuse mount(8) which then tries to mount all
subsequent filesystem types in read-only mode.

Fix the problem by returning EACCES only once we verify that the device
indeed contains an iso9660 filesystem.

Fixes: 17b7f7cf58926844e1dd40f5eb5348d481deca6a
Reported-by: Kent Overstreet <kent.overstreet@...il.com>
Reported-by: Karel Zak <kzak@...hat.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/isofs/inode.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/fs/isofs/inode.c
+++ b/fs/isofs/inode.c
@@ -687,6 +687,11 @@ static int isofs_fill_super(struct super
 	pri_bh = NULL;
 
 root_found:
+	/* We don't support read-write mounts */
+	if (!(s->s_flags & MS_RDONLY)) {
+		error = -EACCES;
+		goto out_freebh;
+	}
 
 	if (joliet_level && (pri == NULL || !opt.rock)) {
 		/* This is the case of Joliet with the norock mount flag.
@@ -1501,9 +1506,6 @@ struct inode *__isofs_iget(struct super_
 static struct dentry *isofs_mount(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
-	/* We don't support read-write mounts */
-	if (!(flags & MS_RDONLY))
-		return ERR_PTR(-EACCES);
 	return mount_bdev(fs_type, flags, dev_name, data, isofs_fill_super);
 }