[ 3.5.y.z extended stable ] Patch "isofs: Refuse RW mount of the filesystem instead of making it" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    isofs: Refuse RW mount of the filesystem instead of making it

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From d08b32b423be5185128c6cc512b83460e292e194 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack at suse.cz>
Date: Thu, 25 Jul 2013 11:49:11 +0200
Subject: [PATCH] isofs: Refuse RW mount of the filesystem instead of making it
 RO

commit 17b7f7cf58926844e1dd40f5eb5348d481deca6a upstream.

Refuse RW mount of isofs filesystem. So far we just silently changed it
to RO mount but when the media is writeable, block layer won't notice
this change and thus will think device is used RW and will block eject
button of the drive. That is unexpected by users because for
non-writeable media eject button works just fine.

Userspace mount(8) command handles this just fine and retries mounting
with MS_RDONLY set so userspace shouldn't see any regression.  Plus any
tool mounting isofs is likely confronted with the case of read-only
media where block layer already refuses to mount the filesystem without
MS_RDONLY set so our behavior shouldn't be anything new for it.

Reported-by: Hui Wang <hui.wang at canonical.com>
Signed-off-by: Jan Kara <jack at suse.cz>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/isofs/inode.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/fs/isofs/inode.c b/fs/isofs/inode.c
index 29037c3..e92a342 100644
--- a/fs/isofs/inode.c
+++ b/fs/isofs/inode.c
@@ -119,8 +119,8 @@ static void destroy_inodecache(void)

 static int isofs_remount(struct super_block *sb, int *flags, char *data)
 {
-	/* we probably want a lot more here */
-	*flags |= MS_RDONLY;
+	if (!(*flags & MS_RDONLY))
+		return -EROFS;
 	return 0;
 }

@@ -769,15 +769,6 @@ root_found:
 	 */
 	s->s_maxbytes = 0x80000000000LL;

-	/*
-	 * The CDROM is read-only, has no nodes (devices) on it, and since
-	 * all of the files appear to be owned by root, we really do not want
-	 * to allow suid.  (suid or devices will not show up unless we have
-	 * Rock Ridge extensions)
-	 */
-
-	s->s_flags |= MS_RDONLY /* | MS_NODEV | MS_NOSUID */;
-
 	/* Set this for reference. Its not currently used except on write
 	   which we don't have .. */

@@ -1536,6 +1527,9 @@ struct inode *isofs_iget(struct super_block *sb,
 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);
 }

--
1.8.3.2