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Subject[PATCH] mtd: Do not corrupt backing device for inode
Date
We cannot modify file->f_mapping->backing_dev_info directly, because it
will corrupt backing device for inode, since inode->i_mapping ==
file->f_mapping (see __dentry_open() in fs/open.c).

So we have to copy f_mapping first.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
drivers/mtd/mtdchar.c | 22 +++++++++++++++++++++-
1 files changed, 21 insertions(+), 1 deletions(-)
diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 5b081cb..d85be4d 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -88,8 +88,23 @@ static int mtd_open(struct inode *inode, struct file *file)
goto out;
}

- if (mtd->backing_dev_info)
+ if (mtd->backing_dev_info) {
+ /*
+ * We assume that file->f_mapping is equal to inode->i_mapping.
+ */
+ BUG_ON(file->f_mapping != inode->i_mapping);
+
+ /*
+ * We cannot modify file->f_mapping->backing_dev_info directly,
+ * because it will corrupt backing device for inode, since
+ * inode->i_mapping is equal to file->f_mapping. So we have to
+ * copy f_mapping first.
+ */
+ file->f_mapping = kmalloc(sizeof(*file->f_mapping), GFP_KERNEL);
+ memcpy(file->f_mapping, inode->i_mapping,
+ sizeof(*file->f_mapping));
file->f_mapping->backing_dev_info = mtd->backing_dev_info;
+ }

/* You can't open it RW if it's not a writeable device */
if ((file->f_mode & FMODE_WRITE) && !(mtd->flags & MTD_WRITEABLE)) {
@@ -129,6 +144,11 @@ static int mtd_close(struct inode *inode, struct file *file)
file->private_data = NULL;
kfree(mfi);

+ if (mtd->backing_dev_info) {
+ kfree(file->f_mapping);
+ file->f_mapping = inode->i_mapping;
+ }
+
return 0;
} /* mtd_close */

--
1.7.0.4


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