// SPDX-License-Identifier: GPL-2.0-only
#include <linux/fs.h>
#include <linux/fs_struct.h>
#include <linux/kernel_read_file.h>
#include <linux/security.h>
#include <linux/vmalloc.h>

/**
 * kernel_read_file() - read file contents into a kernel buffer
 *
 * @file:       file to read from
 * @offset:     where to start reading from (see below).
 * @buf:        pointer to a "void *" buffer for reading into (if
 *              *@buf is NULL, a buffer will be allocated, and
 *              @buf_size will be ignored)
 * @buf_size:   size of buf, if already allocated. If @buf not
 *              allocated, this is the largest size to allocate.
 * @file_size:  if non-NULL, the full size of @file will be
 *              written here.
 * @id:         the kernel_read_file_id identifying the type of
 *              file contents being read (for LSMs to examine)
 *
 * @offset must be 0 unless both @buf and @file_size are non-NULL
 * (i.e. the caller must be expecting to read partial file contents
 * via an already-allocated @buf, in at most @buf_size chunks, and
 * will be able to determine when the entire file was read by
 * checking @file_size). This isn't a recommended way to read a
 * file, though, since it is possible that the contents might
 * change between calls to kernel_read_file().
 *
 * Returns number of bytes read (no single read will be bigger
 * than SSIZE_MAX), or negative on error.
 *
 */
ssize_t kernel_read_file(struct file *file, loff_t offset, void **buf,
                         size_t buf_size, size_t *file_size,
                         enum kernel_read_file_id id)
{
        loff_t i_size, pos;
        ssize_t copied;
        void *allocated = NULL;
        bool whole_file;
        int ret;

        if (offset != 0 && (!*buf || !file_size))
                return -EINVAL;

        if (!S_ISREG(file_inode(file)->i_mode))
                return -EINVAL;

        ret = deny_write_access(file);
        if (ret)
                return ret;

        i_size = i_size_read(file_inode(file));
        if (i_size <= 0) {
                ret = -EINVAL;
                goto out;
        }
        /* The file is too big for sane activities. */
        if (i_size > SSIZE_MAX) {
                ret = -EFBIG;
                goto out;
        }
        /* The entire file cannot be read in one buffer. */
        if (!file_size && offset == 0 && i_size > buf_size) {
                ret = -EFBIG;
                goto out;
        }

        whole_file = (offset == 0 && i_size <= buf_size);
        ret = security_kernel_read_file(file, id, whole_file);
        if (ret)
                goto out;

        if (file_size)
                *file_size = i_size;

        if (!*buf)
                *buf = allocated = vmalloc(i_size);
        if (!*buf) {
                ret = -ENOMEM;
                goto out;
        }

        pos = offset;
        copied = 0;
        while (copied < buf_size) {
                ssize_t bytes;
                size_t wanted = min_t(size_t, buf_size - copied,
                                              i_size - pos);

                bytes = kernel_read(file, *buf + copied, wanted, &pos);
                if (bytes < 0) {
                        ret = bytes;
                        goto out_free;
                }

                if (bytes == 0)
                        break;
                copied += bytes;
        }

        if (whole_file) {
                if (pos != i_size) {
                        ret = -EIO;
                        goto out_free;
                }

                ret = security_kernel_post_read_file(file, *buf, i_size, id);
        }

out_free:
        if (ret < 0) {
                if (allocated) {
                        vfree(*buf);
                        *buf = NULL;
                }
        }

out:
        allow_write_access(file);
        return ret == 0 ? copied : ret;
}
EXPORT_SYMBOL_GPL(kernel_read_file);

ssize_t kernel_read_file_from_path(const char *path, loff_t offset, void **buf,
                                   size_t buf_size, size_t *file_size,
                                   enum kernel_read_file_id id)
{
        struct file *file;
        ssize_t ret;

        if (!path || !*path)
                return -EINVAL;

        file = filp_open(path, O_RDONLY, 0);
        if (IS_ERR(file))
                return PTR_ERR(file);

        ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
        fput(file);
        return ret;
}
EXPORT_SYMBOL_GPL(kernel_read_file_from_path);

ssize_t kernel_read_file_from_path_initns(const char *path, loff_t offset,
                                          void **buf, size_t buf_size,
                                          size_t *file_size,
                                          enum kernel_read_file_id id)
{
        struct file *file;
        struct path root;
        ssize_t ret;

        if (!path || !*path)
                return -EINVAL;

        task_lock(&init_task);
        get_fs_root(init_task.fs, &root);
        task_unlock(&init_task);

        file = file_open_root(&root, path, O_RDONLY, 0);
        path_put(&root);
        if (IS_ERR(file))
                return PTR_ERR(file);

        ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
        fput(file);
        return ret;
}
EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);

ssize_t kernel_read_file_from_fd(int fd, loff_t offset, void **buf,
                                 size_t buf_size, size_t *file_size,
                                 enum kernel_read_file_id id)
{
        CLASS(fd, f)(fd);

        if (fd_empty(f) || !(fd_file(f)->f_mode & FMODE_READ))
                return -EBADF;

        return kernel_read_file(fd_file(f), offset, buf, buf_size, file_size, id);
}
EXPORT_SYMBOL_GPL(kernel_read_file_from_fd);