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Date: Tue, 7 Jul 2020 16:56:52 -0700
From: Kees Cook <keescook@...omium.org>
To: Scott Branden <scott.branden@...adcom.com>
Cc: Luis Chamberlain <mcgrof@...nel.org>,
Wolfram Sang <wsa@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
David Brown <david.brown@...aro.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Shuah Khan <shuah@...nel.org>, bjorn.andersson@...aro.org,
Shuah Khan <skhan@...uxfoundation.org>,
Arnd Bergmann <arnd@...db.de>,
Mimi Zohar <zohar@...ux.ibm.com>,
"Rafael J . Wysocki" <rafael@...nel.org>,
linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
Olof Johansson <olof@...om.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Dan Carpenter <dan.carpenter@...cle.com>,
Colin Ian King <colin.king@...onical.com>,
Takashi Iwai <tiwai@...e.de>, linux-kselftest@...r.kernel.org,
Andy Gross <agross@...nel.org>,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org
Subject: Re: [PATCH v10 2/9] fs: introduce kernel_pread_file* support
On Mon, Jul 06, 2020 at 04:23:02PM -0700, Scott Branden wrote:
> Add kernel_pread_file* support to kernel to allow for partial read
> of files with an offset into the file.
>
> Signed-off-by: Scott Branden <scott.branden@...adcom.com>
> ---
> fs/exec.c | 93 ++++++++++++++++++++++++--------
> include/linux/kernel_read_file.h | 17 ++++++
> 2 files changed, 87 insertions(+), 23 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 4ea87db5e4d5..e6a8a65f7478 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -928,10 +928,14 @@ struct file *open_exec(const char *name)
> }
> EXPORT_SYMBOL(open_exec);
>
> -int kernel_read_file(struct file *file, void **buf, loff_t *size,
> - loff_t max_size, enum kernel_read_file_id id)
> -{
> - loff_t i_size, pos;
> +int kernel_pread_file(struct file *file, void **buf, loff_t *size,
> + loff_t max_size, loff_t pos,
> + enum kernel_read_file_id id)
> +{
> + loff_t alloc_size;
> + loff_t buf_pos;
> + loff_t read_end;
> + loff_t i_size;
> ssize_t bytes = 0;
> int ret;
>
> @@ -951,21 +955,32 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
> ret = -EINVAL;
> goto out;
> }
> - if (i_size > SIZE_MAX || (max_size > 0 && i_size > max_size)) {
> +
> + /* Default read to end of file */
> + read_end = i_size;
> +
> + /* Allow reading partial portion of file */
> + if ((id == READING_FIRMWARE_PARTIAL_READ) &&
> + (i_size > (pos + max_size)))
> + read_end = pos + max_size;
There's no need to involve "id" here. There are other signals about
what's happening (i.e. pos != 0, max_size != i_size, etc).
> +
> + alloc_size = read_end - pos;
> + if (i_size > SIZE_MAX || (max_size > 0 && alloc_size > max_size)) {
> ret = -EFBIG;
> goto out;
> }
>
> - if (id != READING_FIRMWARE_PREALLOC_BUFFER)
> - *buf = vmalloc(i_size);
> + if ((id != READING_FIRMWARE_PARTIAL_READ) &&
> + (id != READING_FIRMWARE_PREALLOC_BUFFER))
> + *buf = vmalloc(alloc_size);
> if (!*buf) {
> ret = -ENOMEM;
> goto out;
> }
The id usage here was a mistake in upstream, and the series I sent is
trying to clean that up.
Greg, it seems this series is going to end up in your tree due to it
being drivers/misc? I guess I need to direct my series to Greg then, but
get LSM folks Acks.
>
> - pos = 0;
> - while (pos < i_size) {
> - bytes = kernel_read(file, *buf + pos, i_size - pos, &pos);
> + buf_pos = 0;
> + while (pos < read_end) {
> + bytes = kernel_read(file, *buf + buf_pos, read_end - pos, &pos);
> if (bytes < 0) {
> ret = bytes;
> goto out_free;
> @@ -973,20 +988,23 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
>
> if (bytes == 0)
> break;
> +
> + buf_pos += bytes;
> }
>
> - if (pos != i_size) {
> + if (pos != read_end) {
> ret = -EIO;
> goto out_free;
> }
>
> - ret = security_kernel_post_read_file(file, *buf, i_size, id);
> + ret = security_kernel_post_read_file(file, *buf, alloc_size, id);
> if (!ret)
> *size = pos;
This call cannot be inside kernel_pread_file(): any future LSMs will see
a moving window of contents, etc. It'll need to be in kernel_read_file()
proper.
>
> out_free:
> if (ret < 0) {
> - if (id != READING_FIRMWARE_PREALLOC_BUFFER) {
> + if ((id != READING_FIRMWARE_PARTIAL_READ) &&
> + (id != READING_FIRMWARE_PREALLOC_BUFFER)) {
> vfree(*buf);
> *buf = NULL;
> }
> @@ -996,10 +1014,18 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
> allow_write_access(file);
> return ret;
> }
> +
> +int kernel_read_file(struct file *file, void **buf, loff_t *size,
> + loff_t max_size, enum kernel_read_file_id id)
> +{
> + return kernel_pread_file(file, buf, size, max_size, 0, id);
> +}
> EXPORT_SYMBOL_GPL(kernel_read_file);
>
> -int kernel_read_file_from_path(const char *path, void **buf, loff_t *size,
> - loff_t max_size, enum kernel_read_file_id id)
> +int kernel_pread_file_from_path(const char *path, void **buf,
> + loff_t *size,
> + loff_t max_size, loff_t pos,
> + enum kernel_read_file_id id)
> {
> struct file *file;
> int ret;
> @@ -1011,15 +1037,22 @@ int kernel_read_file_from_path(const char *path, void **buf, loff_t *size,
> if (IS_ERR(file))
> return PTR_ERR(file);
>
> - ret = kernel_read_file(file, buf, size, max_size, id);
> + ret = kernel_pread_file(file, buf, size, max_size, pos, id);
> fput(file);
> return ret;
> }
> +
> +int kernel_read_file_from_path(const char *path, void **buf, loff_t *size,
> + loff_t max_size, enum kernel_read_file_id id)
> +{
> + return kernel_pread_file_from_path(path, buf, size, max_size, 0, id);
> +}
> EXPORT_SYMBOL_GPL(kernel_read_file_from_path);
>
> -int kernel_read_file_from_path_initns(const char *path, void **buf,
> - loff_t *size, loff_t max_size,
> - enum kernel_read_file_id id)
> +int kernel_pread_file_from_path_initns(const char *path, void **buf,
> + loff_t *size,
> + loff_t max_size, loff_t pos,
> + enum kernel_read_file_id id)
> {
> struct file *file;
> struct path root;
> @@ -1037,14 +1070,22 @@ 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, size, max_size, id);
> + ret = kernel_pread_file(file, buf, size, max_size, pos, id);
> fput(file);
> return ret;
> }
> +
> +int kernel_read_file_from_path_initns(const char *path, void **buf,
> + loff_t *size, loff_t max_size,
> + enum kernel_read_file_id id)
> +{
> + return kernel_pread_file_from_path_initns(path, buf, size, max_size, 0, id);
> +}
> EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
>
> -int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
> - enum kernel_read_file_id id)
> +int kernel_pread_file_from_fd(int fd, void **buf, loff_t *size,
> + loff_t max_size, loff_t pos,
> + enum kernel_read_file_id id)
> {
> struct fd f = fdget(fd);
> int ret = -EBADF;
> @@ -1052,11 +1093,17 @@ int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
> if (!f.file)
> goto out;
>
> - ret = kernel_read_file(f.file, buf, size, max_size, id);
> + ret = kernel_pread_file(f.file, buf, size, max_size, pos, id);
> out:
> fdput(f);
> return ret;
> }
> +
> +int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
> + enum kernel_read_file_id id)
> +{
> + return kernel_pread_file_from_fd(fd, buf, size, max_size, 0, id);
> +}
> EXPORT_SYMBOL_GPL(kernel_read_file_from_fd);
For each of these execution path, the mapping to LSM hooks is:
- all path must call security_kernel_read_file(file, id) before reading
(this appears to be fine as-is in your series).
- anything doing a "full" read needs to call
security_kernel_post_read_file() with the file and full buffer, size,
etc (so all the kernel_read_file*() paths). I imagine instead of
adding 3 copy/pasted versions of this, it may be possible to refactor
the helpers into a single core "full" caller that takes struct file,
or doing some logic in kernel_pread_file() that notices it has the
entire file in the buffer and doing the call then.
As an example of what I mean about doing the call, here's how I might
imagine it for one of the paths if it took struct file:
int kernel_read_file_from_file(struct file *file, void **buf, loff_t *size,
loff_t max_size, enum kernel_read_file_id id)
{
int ret;
ret = kernel_pread_file_from_file(file, buf, size, max_size, 0, id);
if (ret)
return ret;
return security_kernel_post_read_file(file, buf, *size, id);
}
>
> #if defined(CONFIG_HAVE_AOUT) || defined(CONFIG_BINFMT_FLAT) || \
> diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h
> index 53f5ca41519a..f061ccb8d0b4 100644
> --- a/include/linux/kernel_read_file.h
> +++ b/include/linux/kernel_read_file.h
> @@ -8,6 +8,7 @@
> #define __kernel_read_file_id(id) \
> id(UNKNOWN, unknown) \
> id(FIRMWARE, firmware) \
> + id(FIRMWARE_PARTIAL_READ, firmware) \
> id(FIRMWARE_PREALLOC_BUFFER, firmware) \
> id(FIRMWARE_EFI_EMBEDDED, firmware) \
And again, sorry that this was in here as a misleading example.
> id(MODULE, kernel-module) \
> @@ -36,15 +37,31 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
> return kernel_read_file_str[id];
> }
>
> +int kernel_pread_file(struct file *file,
> + void **buf, loff_t *size, loff_t pos,
> + loff_t max_size,
> + enum kernel_read_file_id id);
> int kernel_read_file(struct file *file,
> void **buf, loff_t *size, loff_t max_size,
> enum kernel_read_file_id id);
> +int kernel_pread_file_from_path(const char *path,
> + void **buf, loff_t *size, loff_t pos,
> + loff_t max_size,
> + enum kernel_read_file_id id);
> int kernel_read_file_from_path(const char *path,
> void **buf, loff_t *size, loff_t max_size,
> enum kernel_read_file_id id);
> +int kernel_pread_file_from_path_initns(const char *path,
> + void **buf, loff_t *size, loff_t pos,
> + loff_t max_size,
> + enum kernel_read_file_id id);
> int kernel_read_file_from_path_initns(const char *path,
> void **buf, loff_t *size, loff_t max_size,
> enum kernel_read_file_id id);
> +int kernel_pread_file_from_fd(int fd,
> + void **buf, loff_t *size, loff_t pos,
> + loff_t max_size,
> + enum kernel_read_file_id id);
> int kernel_read_file_from_fd(int fd,
> void **buf, loff_t *size, loff_t max_size,
> enum kernel_read_file_id id);
I remain concerned that adding these helpers will lead a poor
interaction with LSMs, but I guess I get to hold my tongue. :)
--
Kees Cook
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