Commit 0fa8e084 authored by Kees Cook's avatar Kees Cook Committed by Greg Kroah-Hartman
Browse files

fs/kernel_file_read: Add "offset" arg for partial reads 



To perform partial reads, callers of kernel_read_file*() must have a
non-NULL file_size argument and a preallocated buffer. The new "offset"
argument can then be used to seek to specific locations in the file to
fill the buffer to, at most, "buf_size" per call.

Where possible, the LSM hooks can report whether a full file has been
read or not so that the contents can be reasoned about.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201002173828.2099543-14-keescook@chromium.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 34736dae

drivers/base/firmware_loader/main.c

+1 −1
Original line number Diff line number Diff line
@@ -499,7 +499,7 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv, 
		fw_priv->size = 0;



		/* load firmware files from the mount namespace of init */

		rc = kernel_read_file_from_path_initns(path, &buffer, msize,

		rc = kernel_read_file_from_path_initns(path, 0, &buffer, msize,

						       NULL,

						       READING_FIRMWARE);

		if (rc < 0) {

fs/kernel_read_file.c

+54 −24
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
 * 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)
@@ -19,19 +20,31 @@ 
 * @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 INT_MAX), or negative on error.

 *

 */

int kernel_read_file(struct file *file, void **buf,

int 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 bytes = 0;

	size_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;
@@ -39,19 +52,27 @@ int kernel_read_file(struct file *file, void **buf, 
	if (ret)

		return ret;



	ret = security_kernel_read_file(file, id, true);

	if (ret)

		goto out;



	i_size = i_size_read(file_inode(file));

	if (i_size <= 0) {

		ret = -EINVAL;

		goto out;

	}

	if (i_size > INT_MAX || i_size > buf_size) {

	/* The file is too big for sane activities. */

	if (i_size > INT_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;
@@ -62,9 +83,14 @@ int kernel_read_file(struct file *file, void **buf, 
		goto out;

	}



	pos = 0;

	while (pos < i_size) {

		bytes = kernel_read(file, *buf + pos, i_size - pos, &pos);

	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;
@@ -72,14 +98,17 @@ int kernel_read_file(struct file *file, void **buf, 


		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) {
@@ -91,11 +120,11 @@ out_free: 


out:

	allow_write_access(file);

	return ret == 0 ? pos : ret;

	return ret == 0 ? copied : ret;

}

EXPORT_SYMBOL_GPL(kernel_read_file);



int kernel_read_file_from_path(const char *path, void **buf,

int 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)

{
@@ -109,14 +138,15 @@ int kernel_read_file_from_path(const char *path, void **buf, 
	if (IS_ERR(file))

		return PTR_ERR(file);



	ret = kernel_read_file(file, buf, buf_size, file_size, id);

	ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);

	fput(file);

	return ret;

}

EXPORT_SYMBOL_GPL(kernel_read_file_from_path);



int kernel_read_file_from_path_initns(const char *path, void **buf,

				      size_t buf_size, size_t *file_size,

int 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;
@@ -135,14 +165,14 @@ int kernel_read_file_from_path_initns(const char *path, void **buf, 
	if (IS_ERR(file))

		return PTR_ERR(file);



	ret = kernel_read_file(file, buf, buf_size, file_size, id);

	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);



int kernel_read_file_from_fd(int fd, void **buf, size_t buf_size,

			     size_t *file_size,

int 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)

{

	struct fd f = fdget(fd);
@@ -151,7 +181,7 @@ int kernel_read_file_from_fd(int fd, void **buf, size_t buf_size, 
	if (!f.file)

		goto out;



	ret = kernel_read_file(f.file, buf, buf_size, file_size, id);

	ret = kernel_read_file(f.file, offset, buf, buf_size, file_size, id);

out:

	fdput(f);

	return ret;

include/linux/kernel_read_file.h

+4 −4
Original line number Diff line number Diff line
@@ -35,19 +35,19 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id) 
	return kernel_read_file_str[id];

}



int kernel_read_file(struct file *file,

int 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);

int kernel_read_file_from_path(const char *path,

int 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);

int kernel_read_file_from_path_initns(const char *path,

int 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);

int kernel_read_file_from_fd(int fd,

int 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);

kernel/kexec_file.c

+2 −2
Original line number Diff line number Diff line
@@ -221,7 +221,7 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd, 
	int ret;

	void *ldata;



	ret = kernel_read_file_from_fd(kernel_fd, &image->kernel_buf,

	ret = kernel_read_file_from_fd(kernel_fd, 0, &image->kernel_buf,

				       INT_MAX, NULL, READING_KEXEC_IMAGE);

	if (ret < 0)

		return ret;
@@ -241,7 +241,7 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd, 
#endif

	/* It is possible that there no initramfs is being loaded */

	if (!(flags & KEXEC_FILE_NO_INITRAMFS)) {

		ret = kernel_read_file_from_fd(initrd_fd, &image->initrd_buf,

		ret = kernel_read_file_from_fd(initrd_fd, 0, &image->initrd_buf,

					       INT_MAX, NULL,

					       READING_KEXEC_INITRAMFS);

		if (ret < 0)

kernel/module.c

+1 −1
Original line number Diff line number Diff line
@@ -4054,7 +4054,7 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags) 
		      |MODULE_INIT_IGNORE_VERMAGIC))

		return -EINVAL;



	err = kernel_read_file_from_fd(fd, &hdr, INT_MAX, NULL,

	err = kernel_read_file_from_fd(fd, 0, &hdr, INT_MAX, NULL,

				       READING_MODULE);

	if (err < 0)

		return err;

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