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

[firefly-linux-kernel-4.4.55.git] / fs / open.c

diff --git a/fs/open.c b/fs/open.c
index 8111947905d8ebe814a0f38fd17eb7ff6b4f4135..e12f1701032428ae3dd8476043a0103bac2f385f 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -730,6 +730,35 @@ out:
        return error;
 }
 
+/*
+ * You have to be very careful that these write
+ * counts get cleaned up in error cases and
+ * upon __fput().  This should probably never
+ * be called outside of __dentry_open().
+ */
+static inline int __get_file_write_access(struct inode *inode,
+                                         struct vfsmount *mnt)
+{
+       int error;
+       error = get_write_access(inode);
+       if (error)
+               return error;
+       /*
+        * Do not take mount writer counts on
+        * special files since no writes to
+        * the mount itself will occur.
+        */
+       if (!special_file(inode->i_mode)) {
+               /*
+                * Balanced in __fput()
+                */
+               error = mnt_want_write(mnt);
+               if (error)
+                       put_write_access(inode);
+       }
+       return error;
+}
+
 static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
                                        int flags, struct file *f,
                                        int (*open)(struct inode *, struct file *))
@@ -742,7 +771,7 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
                                FMODE_PREAD | FMODE_PWRITE;
        inode = dentry->d_inode;
        if (f->f_mode & FMODE_WRITE) {
-               error = get_write_access(inode);
+               error = __get_file_write_access(inode, mnt);
                if (error)
                        goto cleanup_file;
        }
@@ -784,8 +813,11 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
 
 cleanup_all:
        fops_put(f->f_op);
-       if (f->f_mode & FMODE_WRITE)
+       if (f->f_mode & FMODE_WRITE) {
                put_write_access(inode);
+               if (!special_file(inode->i_mode))
+                       mnt_drop_write(mnt);
+       }
        file_kill(f);
        f->f_path.dentry = NULL;
        f->f_path.mnt = NULL;