[RFC PATCH] ima: force the re-evaluation of files on untrusted file systems

[Alban Crequy]

On Mon, Feb 5, 2018 at 2:40 PM, Mimi Zohar <zohar at linux.vnet.ibm.com> wrote:
> On filesystems, such as fuse or remote filesystems, that we can not
> detect or rely on the filesystem to tell us when a file has changed,
> always re-measure, re-appraise, and/or re-audit the file.
>
> Signed-of-by: Mimi Zohar <zohar at linux.vnet.ibm.com>
>
> ---
> Hi Miklos,
>
> Was something like this what you had in mind?
>
> Mimi
> ---
>  security/integrity/ima/ima_main.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 6d78cb26784d..a428bd75232e 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -170,6 +170,7 @@ static int process_measurement(struct file *file, char *buf, loff_t size,
>                                int mask, enum ima_hooks func, int opened)
>  {
>         struct inode *inode = file_inode(file);
> +       struct dentry *dentry = file_dentry(file);
>         struct integrity_iint_cache *iint = NULL;
>         struct ima_template_desc *template_desc;
>         char *pathbuf = NULL;
> @@ -228,9 +229,16 @@ static int process_measurement(struct file *file, char *buf, loff_t size,
>                                  IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
>                                  IMA_ACTION_FLAGS);
>
> -       if (test_and_clear_bit(IMA_CHANGE_XATTR, &iint->atomic_flags))
> -               /* reset all flags if ima_inode_setxattr was called */
> +       /*
> +        * Re-measure, re-appraise, and/or re-audit a file, if the security
> +        * xattrs changed or if the file is on an untrusted file system
> +        * (eg. FUSE, remote filesystems).
> +        */
> +       if (test_and_clear_bit(IMA_CHANGE_XATTR, &iint->atomic_flags) ||
> +           (dentry->d_op && dentry->d_op->d_revalidate)) {

It seems dangerous to rely implicitly on "d_revalidate != NULL". vfat
has a d_revalidate for handling 8.3 filenames but it's not a network
filesystem.
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