linux-kernel - [PATCH 3.16 139/306] isofs: Do not return EACCES for unknown filesystems

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Message-ID: <lsq.1487198500.913306472@decadent.org.uk>
Date:   Wed, 15 Feb 2017 22:41:40 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Karel Zak" <kzak@...hat.com>,
        "Kent Overstreet" <kent.overstreet@...il.com>,
        "Jan Kara" <jack@...e.cz>
Subject: [PATCH 3.16 139/306] isofs: Do not return EACCES for unknown
 filesystems

3.16.40-rc1 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: Ben Hutchings <ben@...adent.org.uk>
---
 fs/isofs/inode.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/fs/isofs/inode.c
+++ b/fs/isofs/inode.c
@@ -711,6 +711,11 @@ 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.
@@ -1523,9 +1528,6 @@ 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);
 }