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// Copyright 2024 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
#include <fcntl.h>
#include <stddef.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>
// ShmemFile is shared memory region wrapper.
class ShmemFile
{
public:
// Maps shared memory region of size 'size' from a new temp file.
ShmemFile(size_t size)
{
char file_name[] = "syz.XXXXXX";
fd_ = mkstemp(file_name);
if (fd_ == -1)
failmsg("shmem open failed", "file=%s", file_name);
// OpenBSD has neither fallocate nor posix_fallocate.
if (ftruncate(fd_, size))
failmsg("shmem ftruncate failed", "size=%zu", size);
Mmap(fd_, nullptr, size, true);
if (unlink(file_name))
fail("shmem unlink failed");
}
// Maps shared memory region from the file 'fd' in read/write or write-only mode,
// preferably at the address 'preferred'.
ShmemFile(int fd, void* preferred, size_t size, bool write)
{
Mmap(fd, preferred, size, write);
}
~ShmemFile()
{
if (munmap(mem_, size_))
fail("shmem munmap failed");
if (fd_ != -1)
close(fd_);
}
// Prevents any future modifications to the region.
void Seal()
{
if (mprotect(mem_, size_, PROT_READ))
fail("shmem mprotect failed");
if (fd_ != -1)
close(fd_);
fd_ = -1;
}
int FD() const
{
return fd_;
}
void* Mem() const
{
return mem_;
}
private:
void* mem_ = nullptr;
size_t size_ = 0;
int fd_ = -1;
void Mmap(int fd, void* preferred, size_t size, bool write)
{
size_ = size;
mem_ = mmap(preferred, size, PROT_READ | (write ? PROT_WRITE : 0), MAP_SHARED, fd, 0);
if (mem_ == MAP_FAILED)
failmsg("shmem mmap failed", "size=%zu", size);
}
ShmemFile(const ShmemFile&) = delete;
ShmemFile& operator=(const ShmemFile&) = delete;
};
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