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fdb71cdf8f
This adds support for MS_RDONLY, a mount flag that tells the kernel to disallow any attempts to write to the newly mounted filesystem. As this flag is per-mount, and different mounts of the same filesystems (such as in case of bind mounts) can have different mutability settings, you have to go though a custody to find out if the filesystem is mounted read-only, instead of just asking the filesystem itself whether it's inherently read-only. This also adds a lot of checks we were previously missing; and moves some of them to happen after more specific checks (such as regular permission checks). One outstanding hole in this system is sys$mprotect(PROT_WRITE), as there's no way we can know if the original file description this region has been mounted from had been opened through a readonly mount point. Currently, we always allow such sys$mprotect() calls to succeed, which effectively allows anyone to circumvent the effect of MS_RDONLY. We should solve this one way or another.
71 lines
2.3 KiB
C++
71 lines
2.3 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <AK/StringBuilder.h>
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#include <AK/StringView.h>
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#include <AK/Vector.h>
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#include <Kernel/FileSystem/Custody.h>
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#include <Kernel/FileSystem/Inode.h>
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namespace Kernel {
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Custody::Custody(Custody* parent, const StringView& name, Inode& inode, int mount_flags)
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: m_parent(parent)
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, m_name(name)
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, m_inode(inode)
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, m_mount_flags(mount_flags)
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{
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}
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Custody::~Custody()
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{
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}
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String Custody::absolute_path() const
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{
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if (!parent())
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return "/";
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Vector<const Custody*, 32> custody_chain;
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for (auto* custody = this; custody; custody = custody->parent())
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custody_chain.append(custody);
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StringBuilder builder;
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for (int i = custody_chain.size() - 2; i >= 0; --i) {
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builder.append('/');
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builder.append(custody_chain[i]->name().characters());
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}
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return builder.to_string();
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}
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bool Custody::is_readonly() const
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{
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if (m_mount_flags & MS_RDONLY)
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return true;
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return m_inode->fs().is_readonly();
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}
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}
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