mtd: mtdchar: Do not corrupt backing device of device node inode
We cannot modify file->f_mapping->backing_dev_info, because it will corrupt
backing device of device node inode, since file->f_mapping is equal to
inode->i_mapping (see __dentry_open() in fs/open.c).
Let's introduce separate inode for MTD device with appropriate backing
device.
[dwmw2: Refactor to keep it all entirely within mtdchar.c; use iget_locked()]
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index c355491..8bb5e4a 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -15,12 +15,15 @@
#include <linux/smp_lock.h>
#include <linux/backing-dev.h>
#include <linux/compat.h>
+#include <linux/mount.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/compatmac.h>
#include <asm/uaccess.h>
+#define MTD_INODE_FS_MAGIC 0x11307854
+static struct vfsmount *mtd_inode_mnt __read_mostly;
/*
* Data structure to hold the pointer to the mtd device as well
@@ -28,6 +31,7 @@
*/
struct mtd_file_info {
struct mtd_info *mtd;
+ struct inode *ino;
enum mtd_file_modes mode;
};
@@ -64,6 +68,7 @@
int ret = 0;
struct mtd_info *mtd;
struct mtd_file_info *mfi;
+ struct inode *mtd_ino;
DEBUG(MTD_DEBUG_LEVEL0, "MTD_open\n");
@@ -85,11 +90,23 @@
goto out;
}
- if (mtd->backing_dev_info)
- file->f_mapping->backing_dev_info = mtd->backing_dev_info;
+ mtd_ino = iget_locked(mtd_inode_mnt->mnt_sb, devnum);
+ if (!mtd_ino) {
+ put_mtd_device(mtd);
+ ret = -ENOMEM;
+ goto out;
+ }
+ if (mtd_ino->i_state & I_NEW) {
+ mtd_ino->i_private = mtd;
+ mtd_ino->i_mode = S_IFCHR;
+ mtd_ino->i_data.backing_dev_info = mtd->backing_dev_info;
+ unlock_new_inode(mtd_ino);
+ }
+ file->f_mapping = mtd_ino->i_mapping;
/* You can't open it RW if it's not a writeable device */
if ((file->f_mode & FMODE_WRITE) && !(mtd->flags & MTD_WRITEABLE)) {
+ iput(mtd_ino);
put_mtd_device(mtd);
ret = -EACCES;
goto out;
@@ -97,10 +114,12 @@
mfi = kzalloc(sizeof(*mfi), GFP_KERNEL);
if (!mfi) {
+ iput(mtd_ino);
put_mtd_device(mtd);
ret = -ENOMEM;
goto out;
}
+ mfi->ino = mtd_ino;
mfi->mtd = mtd;
file->private_data = mfi;
@@ -122,6 +141,8 @@
if ((file->f_mode & FMODE_WRITE) && mtd->sync)
mtd->sync(mtd);
+ iput(mfi->ino);
+
put_mtd_device(mtd);
file->private_data = NULL;
kfree(mfi);
@@ -951,22 +972,80 @@
#endif
};
+static int mtd_inodefs_get_sb(struct file_system_type *fs_type, int flags,
+ const char *dev_name, void *data,
+ struct vfsmount *mnt)
+{
+ return get_sb_pseudo(fs_type, "mtd_inode:", NULL, MTD_INODE_FS_MAGIC,
+ mnt);
+}
+
+static struct file_system_type mtd_inodefs_type = {
+ .name = "mtd_inodefs",
+ .get_sb = mtd_inodefs_get_sb,
+ .kill_sb = kill_anon_super,
+};
+
+static void mtdchar_notify_add(struct mtd_info *mtd)
+{
+}
+
+static void mtdchar_notify_remove(struct mtd_info *mtd)
+{
+ struct inode *mtd_ino = ilookup(mtd_inode_mnt->mnt_sb, mtd->index);
+
+ if (mtd_ino) {
+ /* Destroy the inode if it exists */
+ mtd_ino->i_nlink = 0;
+ iput(mtd_ino);
+ }
+}
+
+static struct mtd_notifier mtdchar_notifier = {
+ .add = mtdchar_notify_add,
+ .remove = mtdchar_notify_remove,
+};
+
static int __init init_mtdchar(void)
{
- int status;
+ int ret;
- status = __register_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS,
+ ret = __register_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS,
"mtd", &mtd_fops);
- if (status < 0) {
- printk(KERN_NOTICE "Can't allocate major number %d for Memory Technology Devices.\n",
- MTD_CHAR_MAJOR);
+ if (ret < 0) {
+ pr_notice("Can't allocate major number %d for "
+ "Memory Technology Devices.\n", MTD_CHAR_MAJOR);
+ return ret;
}
- return status;
+ ret = register_filesystem(&mtd_inodefs_type);
+ if (ret) {
+ pr_notice("Can't register mtd_inodefs filesystem: %d\n", ret);
+ goto err_unregister_chdev;
+ }
+
+ mtd_inode_mnt = kern_mount(&mtd_inodefs_type);
+ if (IS_ERR(mtd_inode_mnt)) {
+ ret = PTR_ERR(mtd_inode_mnt);
+ pr_notice("Error mounting mtd_inodefs filesystem: %d\n", ret);
+ goto err_unregister_filesystem;
+ }
+ register_mtd_user(&mtdchar_notifier);
+
+ return ret;
+
+err_unregister_filesystem:
+ unregister_filesystem(&mtd_inodefs_type);
+err_unregister_chdev:
+ __unregister_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS, "mtd");
+ return ret;
}
static void __exit cleanup_mtdchar(void)
{
+ unregister_mtd_user(&mtdchar_notifier);
+ mntput(mtd_inode_mnt);
+ unregister_filesystem(&mtd_inodefs_type);
__unregister_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS, "mtd");
}