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

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 [off-list ref]

---
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)) {