From 63a1be14066c6367d37cc792a171d3dfaeac517f Mon Sep 17 00:00:00 2001
From: Sahan Fernando <sahan.h.fernando@gmail.com>
Date: Thu, 13 May 2021 12:19:53 +1000
Subject: [PATCH] Kernel: Don't update write_pos in DoubleBuffer if userspace
 copy fails

---
 Kernel/DoubleBuffer.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Kernel/DoubleBuffer.cpp b/Kernel/DoubleBuffer.cpp
index 2d3b39adac..41236e4c2b 100644
--- a/Kernel/DoubleBuffer.cpp
+++ b/Kernel/DoubleBuffer.cpp
@@ -47,10 +47,10 @@ ssize_t DoubleBuffer::write(const UserOrKernelBuffer& data, size_t size)
     Locker locker(m_lock);
     size_t bytes_to_write = min(size, m_space_for_writing);
     u8* write_ptr = m_write_buffer->data + m_write_buffer->size;
-    m_write_buffer->size += bytes_to_write;
-    compute_lockfree_metadata();
     if (!data.read(write_ptr, bytes_to_write))
         return -EFAULT;
+    m_write_buffer->size += bytes_to_write;
+    compute_lockfree_metadata();
     if (m_unblock_callback && !m_empty)
         m_unblock_callback();
     return (ssize_t)bytes_to_write;