SharedBuffer: Fix a denial of service

It's a very bad idea to increment the refcount on behalf of another
process. That process may (for either benign or evil reasons) not
reference the SharedBuffer, and then we'll be stuck with loads of
SharedBuffers until we OOM.

Instead, increment the refcount when the buffer is mapped. That way, a
buffer is only kept if *someone* has explicitly requested it via
get_shared_buffer.

Fixes #341

1 files changed, 3 insertions, 3 deletions

diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index e051d1ed13..5b143240e3 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -2408,7 +2408,7 @@ int Process::sys$create_shared_buffer(int size, void** buffer)
     int shared_buffer_id = ++s_next_shared_buffer_id;
     auto shared_buffer = make<SharedBuffer>(shared_buffer_id, size);
     shared_buffer->share_with(m_pid);
-    *buffer = shared_buffer->get_address(*this);
+    *buffer = shared_buffer->ref_for_process_and_get_address(*this);
     ASSERT((int)shared_buffer->size() >= size);
 #ifdef SHARED_BUFFER_DEBUG
     kprintf("%s(%u): Created shared buffer %d @ %p (%u bytes, vmo is %u)\n", name().characters(), pid(), shared_buffer_id, *buffer, size, shared_buffer->size());
@@ -2447,7 +2447,7 @@ int Process::sys$release_shared_buffer(int shared_buffer_id)
 #ifdef SHARED_BUFFER_DEBUG
     kprintf("%s(%u): Releasing shared buffer %d, buffer count: %u\n", name().characters(), pid(), shared_buffer_id, shared_buffers().resource().size());
 #endif
-    shared_buffer.release(*this);
+    shared_buffer.deref_for_process(*this);
     return 0;
 }
 
@@ -2463,7 +2463,7 @@ void* Process::sys$get_shared_buffer(int shared_buffer_id)
 #ifdef SHARED_BUFFER_DEBUG
     kprintf("%s(%u): Retaining shared buffer %d, buffer count: %u\n", name().characters(), pid(), shared_buffer_id, shared_buffers().resource().size());
 #endif
-    return shared_buffer.get_address(*this);
+    return shared_buffer.ref_for_process_and_get_address(*this);
 }
 
 int Process::sys$seal_shared_buffer(int shared_buffer_id)