blk-mq-debugfs: don't allow write on attributes with seq_operations set

BugLink: http://bugs.launchpad.net/bugs/1774063
[ Upstream commit 6b136a24b05c81a24e0b648a4bd938bcd0c4f69e ]

Attributes that only implement .seq_ops are read-only, any write to
them should be rejected. But currently kernel would crash when
writing to such debugfs entries, e.g.

chmod +w /sys/kernel/debug/block/<dev>/requeue_list
echo 0 > /sys/kernel/debug/block/<dev>/requeue_list
chmod -w /sys/kernel/debug/block/<dev>/requeue_list

Fix it by returning -EPERM in blk_mq_debugfs_write() when writing to
such attributes.

Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index b56a4f35720d8a46e8a5daf3f2c63a51475308a3..54bd8c31b822d25e35c8807903bef9dffbf1277b 100644 (file)
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -703,7 +703,11 @@ static ssize_t blk_mq_debugfs_write(struct file *file, const char __user *buf,
        const struct blk_mq_debugfs_attr *attr = m->private;
        void *data = d_inode(file->f_path.dentry->d_parent)->i_private;
 
-       if (!attr->write)
+       /*
+        * Attributes that only implement .seq_ops are read-only and 'attr' is
+        * the same with 'data' in this case.
+        */
+       if (attr == data || !attr->write)
                return -EPERM;
 
        return attr->write(data, buf, count, ppos);