summaryrefslogtreecommitdiffstats
path: root/fs/namespace.c
diff options
context:
space:
mode:
Diffstat (limited to 'fs/namespace.c')
-rw-r--r--fs/namespace.c64
1 files changed, 61 insertions, 3 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index f8893dc6a989..df0f7521979a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -431,13 +431,18 @@ int __mnt_want_write_file(struct file *file)
}
/**
- * mnt_want_write_file - get write access to a file's mount
+ * mnt_want_write_file_path - get write access to a file's mount
* @file: the file who's mount on which to take a write
*
* This is like mnt_want_write, but it takes a file and can
* do some optimisations if the file is open for write already
+ *
+ * Called by the vfs for cases when we have an open file at hand, but will do an
+ * inode operation on it (important distinction for files opened on overlayfs,
+ * since the file operations will come from the real underlying file, while
+ * inode operations come from the overlay).
*/
-int mnt_want_write_file(struct file *file)
+int mnt_want_write_file_path(struct file *file)
{
int ret;
@@ -447,6 +452,53 @@ int mnt_want_write_file(struct file *file)
sb_end_write(file->f_path.mnt->mnt_sb);
return ret;
}
+
+static inline int may_write_real(struct file *file)
+{
+ struct dentry *dentry = file->f_path.dentry;
+ struct dentry *upperdentry;
+
+ /* Writable file? */
+ if (file->f_mode & FMODE_WRITER)
+ return 0;
+
+ /* Not overlayfs? */
+ if (likely(!(dentry->d_flags & DCACHE_OP_REAL)))
+ return 0;
+
+ /* File refers to upper, writable layer? */
+ upperdentry = d_real(dentry, NULL, 0, D_REAL_UPPER);
+ if (upperdentry && file_inode(file) == d_inode(upperdentry))
+ return 0;
+
+ /* Lower layer: can't write to real file, sorry... */
+ return -EPERM;
+}
+
+/**
+ * mnt_want_write_file - get write access to a file's mount
+ * @file: the file who's mount on which to take a write
+ *
+ * This is like mnt_want_write, but it takes a file and can
+ * do some optimisations if the file is open for write already
+ *
+ * Mostly called by filesystems from their ioctl operation before performing
+ * modification. On overlayfs this needs to check if the file is on a read-only
+ * lower layer and deny access in that case.
+ */
+int mnt_want_write_file(struct file *file)
+{
+ int ret;
+
+ ret = may_write_real(file);
+ if (!ret) {
+ sb_start_write(file_inode(file)->i_sb);
+ ret = __mnt_want_write_file(file);
+ if (ret)
+ sb_end_write(file_inode(file)->i_sb);
+ }
+ return ret;
+}
EXPORT_SYMBOL_GPL(mnt_want_write_file);
/**
@@ -484,10 +536,16 @@ void __mnt_drop_write_file(struct file *file)
__mnt_drop_write(file->f_path.mnt);
}
-void mnt_drop_write_file(struct file *file)
+void mnt_drop_write_file_path(struct file *file)
{
mnt_drop_write(file->f_path.mnt);
}
+
+void mnt_drop_write_file(struct file *file)
+{
+ __mnt_drop_write(file->f_path.mnt);
+ sb_end_write(file_inode(file)->i_sb);
+}
EXPORT_SYMBOL(mnt_drop_write_file);
static int mnt_make_readonly(struct mount *mnt)