From 2d91761cf6fb79cdc587c90270455396a8170d37 Mon Sep 17 00:00:00 2001
From: Gunnar Beutner <gunnar@beutner.name>
Date: Tue, 13 Apr 2021 19:27:49 +0200
Subject: Kernel: Make sure the offset stays the same when using mremap()

When using mmap() on a file with a non-zero offset subsequent
calls to mremap() would incorrectly reset the offset to zero.
---
 Kernel/Syscalls/mmap.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'Kernel')

diff --git a/Kernel/Syscalls/mmap.cpp b/Kernel/Syscalls/mmap.cpp
index db401a59c5..3e8ede3c8a 100644
--- a/Kernel/Syscalls/mmap.cpp
+++ b/Kernel/Syscalls/mmap.cpp
@@ -566,6 +566,7 @@ KResultOr<FlatPtr> Process::sys$mremap(Userspace<const Syscall::SC_mremap_params
         auto range = old_region->range();
         auto old_name = old_region->name();
         auto old_prot = region_access_flags_to_prot(old_region->access());
+        auto old_offset = old_region->offset_in_vmobject();
         NonnullRefPtr inode = static_cast<SharedInodeVMObject&>(old_region->vmobject()).inode();
 
         // Unmap without deallocating the VM range since we're going to reuse it.
@@ -575,7 +576,7 @@ KResultOr<FlatPtr> Process::sys$mremap(Userspace<const Syscall::SC_mremap_params
 
         auto new_vmobject = PrivateInodeVMObject::create_with_inode(inode);
 
-        auto new_region_or_error = space().allocate_region_with_vmobject(range, new_vmobject, 0, old_name, old_prot, false);
+        auto new_region_or_error = space().allocate_region_with_vmobject(range, new_vmobject, old_offset, old_name, old_prot, false);
         if (new_region_or_error.is_error())
             return new_region_or_error.error().error();
         auto& new_region = *new_region_or_error.value();
-- 
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