[PATCH] r/o bind mounts: elevate write count for ioctls()

Some ioctl()s can cause writes to the filesystem.  Take these, and make them
use mnt_want/drop_write() instead.

[AV: updated]

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 7 insertions, 5 deletions

diff --git a/fs/fat/file.c b/fs/fat/file.c
index c614175876e0..2a3bed967041 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -8,6 +8,7 @@
 
 #include <linux/capability.h>
 #include <linux/module.h>
+#include <linux/mount.h>
 #include <linux/time.h>
 #include <linux/msdos_fs.h>
 #include <linux/smp_lock.h>
@@ -46,10 +47,9 @@ int fat_generic_ioctl(struct inode *inode, struct file *filp,
 
                 mutex_lock(&inode->i_mutex);
 
-                if (IS_RDONLY(inode)) {
-                        err = -EROFS;
-                        goto up;
-                }
+                err = mnt_want_write(filp->f_path.mnt);
+                if (err)
+                        goto up_no_drop_write;
 
                 /*
                  * ATTR_VOLUME and ATTR_DIR cannot be changed; this also
@@ -105,7 +105,9 @@ int fat_generic_ioctl(struct inode *inode, struct file *filp,
 
                 MSDOS_I(inode)->i_attrs = attr & ATTR_UNUSED;
                 mark_inode_dirty(inode);
-        up:
+up:
+                mnt_drop_write(filp->f_path.mnt);
+up_no_drop_write:
                 mutex_unlock(&inode->i_mutex);
                 return err;
         }