On Tue, Feb 16, 2016 at 12:54 PM, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> From: Dmitry Kasatkin <d.kasatkin@xxxxxxxxxxx>
>
> This patch is based on top of the "vfs: support for a common kernel file
> loader" patch set. In general when the kernel is reading a file into
> memory it does not want anything else writing to it.
Oh yes please. Thanks for this! That had bothered me for a long time. :)
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
-Kees
>
> The kernel currently only forbids write access to a file being executed.
> This patch extends this locking to files being read by the kernel.
>
> Changelog:
> - moved function to kernel_read_file() - Mimi
> - updated patch description - Mimi
>
> Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> ---
> fs/exec.c | 29 +++++++++++++++++++++--------
> 1 file changed, 21 insertions(+), 8 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 604f669..1b7d617 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -846,15 +846,25 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
> if (ret)
> return ret;
>
> + ret = deny_write_access(file);
> + if (ret)
> + return ret;
> +
> i_size = i_size_read(file_inode(file));
> - if (max_size > 0 && i_size > max_size)
> - return -EFBIG;
> - if (i_size <= 0)
> - return -EINVAL;
> + if (max_size > 0 && i_size > max_size) {
> + ret = -EFBIG;
> + goto out;
> + }
> + if (i_size <= 0) {
> + ret = -EINVAL;
> + goto out;
> + }
>
> *buf = vmalloc(i_size);
> - if (!*buf)
> - return -ENOMEM;
> + if (!*buf) {
> + ret = -ENOMEM;
> + goto out;
> + }
>
> pos = 0;
> while (pos < i_size) {
> @@ -872,18 +882,21 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
>
> if (pos != i_size) {
> ret = -EIO;
> - goto out;
> + goto out_free;
> }
>
> ret = security_kernel_post_read_file(file, *buf, i_size, id);
> if (!ret)
> *size = pos;
>
> -out:
> +out_free:
> if (ret < 0) {
> vfree(*buf);
> *buf = NULL;
> }
> +
> +out:
> + allow_write_access(file);
> return ret;
> }
> EXPORT_SYMBOL_GPL(kernel_read_file);
> --
> 2.1.0
>
--
Kees Cook
Chrome OS & Brillo Security
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
