From: Valerie Aurora <vaurora@xxxxxxxxxx>
Passing the CL_MAKE_HARD_READONLY flag to clone_mnt() causes the clone
to fail if the source superblock is not read-only. If it is
read-only, it increments the hard read-only users and sets the
MNT_HARD_READONLY flag in the vfsmount. When the mount is freed via
free_vfsmnt(), automatically decrement the hard read-only users count.
Cc: Ram Pai <linuxram@xxxxxxxxxx>
Signed-off-by: Valerie Aurora <valerie.aurora@xxxxxxxxx>
---
fs/namespace.c | 18 ++++++++++++++++++
fs/pnode.h | 1 +
include/linux/mount.h | 1 +
3 files changed, 20 insertions(+), 0 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 454d7ad..0f028e0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -417,6 +417,12 @@ EXPORT_SYMBOL(simple_set_mnt);
void free_vfsmnt(struct vfsmount *mnt)
{
kfree(mnt->mnt_devname);
+ if (mnt->mnt_flags & MNT_HARD_READONLY) {
+ BUG_ON(mnt->mnt_sb->s_hard_readonly_users <= 0);
+ down_write(&mnt->mnt_sb->s_umount);
+ mnt->mnt_sb->s_hard_readonly_users--;
+ up_write(&mnt->mnt_sb->s_umount);
+ }
mnt_free_id(mnt);
#ifdef CONFIG_SMP
free_percpu(mnt->mnt_writers);
@@ -602,6 +608,16 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
if ((flag & CL_NO_SLAVE) && (IS_MNT_SLAVE(old)))
return ERR_PTR(-EINVAL);
+ if (flag & CL_MAKE_HARD_READONLY) {
+ down_write(&sb->s_umount);
+ if (!(sb->s_flags & MS_RDONLY)) {
+ up_write(&sb->s_umount);
+ return ERR_PTR(-EBUSY);
+ }
+ sb->s_hard_readonly_users++;
+ up_write(&sb->s_umount);
+ }
+
mnt = alloc_vfsmnt(old->mnt_devname);
if (!mnt)
return ERR_PTR(-ENOMEM);
@@ -637,6 +653,8 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
}
if (flag & CL_MAKE_SHARED)
set_mnt_shared(mnt);
+ if (flag & CL_MAKE_HARD_READONLY)
+ mnt->mnt_flags |= MNT_HARD_READONLY;
/* stick the duplicate mount on the same expiry list
* as the original if that was on one */
diff --git a/fs/pnode.h b/fs/pnode.h
index 8920e47..dc7b468 100644
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -24,6 +24,7 @@
#define CL_PRIVATE 0x10
#define CL_NO_SHARED 0x20
#define CL_NO_SLAVE 0x40
+#define CL_MAKE_HARD_READONLY 0x80
static inline void set_mnt_shared(struct vfsmount *mnt)
{
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 5e7a594..44aa119 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -45,6 +45,7 @@ struct mnt_namespace;
#define MNT_INTERNAL 0x4000
+#define MNT_HARD_READONLY 0x8000 /* has a hard read-only ref on the sb */
struct vfsmount {
struct list_head mnt_hash;
--
1.7.0.4
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