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Kernel: Use FixedStringBuffer for fixed-length strings in syscalls

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Using the kernel stack is preferable, especially when the examined
strings should be limited to a reasonable length.

This is a small improvement, because if we don't actually move these
strings then we don't need to own heap allocations for them during the
syscall handler function scope.

In addition to that, some kernel strings are known to be limited, like
the hostname string, for these strings we also can use FixedStringBuffer
to store and copy to and from these buffers, without using any heap
allocations at all.
This commit is contained in:
Liav A 2023-07-17 19:22:01 +03:00 • committed by Andrew Kaster
parent 3fd4997fc2
commit d8b514873f
13 changed files with 100 additions and 46 deletions
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6
Kernel/Syscalls/mount.cpp
View file

@ -5,6 +5,7 @@
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/FixedStringBuffer.h>
#include <Kernel/FileSystem/Custody.h>
#include <Kernel/FileSystem/MountFile.h>
#include <Kernel/FileSystem/VirtualFileSystem.h>
@ -20,14 +21,15 @@ ErrorOr<FlatPtr> Process::sys$fsopen(Userspace<Syscall::SC_fsopen_params const*>
if (!credentials->is_superuser())
return Error::from_errno(EPERM);
auto params = TRY(copy_typed_from_user(user_params));
auto fs_type_string = TRY(try_copy_kstring_from_user(params.fs_type));
// NOTE: 16 characters should be enough for any fstype today and in the future.
auto fs_type_string = TRY(get_syscall_name_string_fixed_buffer<16>(params.fs_type));
// NOTE: If some userspace program uses MS_REMOUNT, return EINVAL to indicate that we never want this
// flag to appear in the mount table...
if (params.flags & MS_REMOUNT || params.flags & MS_BIND)
return Error::from_errno(EINVAL);
auto const* fs_type_initializer = TRY(VirtualFileSystem::find_filesystem_type_initializer(fs_type_string->view()));
auto const* fs_type_initializer = TRY(VirtualFileSystem::find_filesystem_type_initializer(fs_type_string.representable_view()));
VERIFY(fs_type_initializer);
auto mount_file = TRY(MountFile::create(*fs_type_initializer, params.flags));
auto description = TRY(OpenFileDescription::try_create(move(mount_file)));