[RFC PATCH v5 1/2] ima: force re-appraisal on filesystems with FS_IMA_NO_CACHE

[Dongsu Park <dongsu@xxxxxxxxxx>]

From: Alban Crequy <alban@xxxxxxxxxx>

This patch forces files to be re-measured, re-appraised and re-audited
on file systems with the feature flag FS_IMA_NO_CACHE. In that way,
cached integrity results won't be used.

Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-integrity@xxxxxxxxxxxxxxx
Cc: linux-security-module@xxxxxxxxxxxxxxx
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
Cc: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Acked-by: "Serge E. Hallyn" <serge@xxxxxxxxxx>
Acked-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
Tested-by: Dongsu Park <dongsu@xxxxxxxxxx>
Signed-off-by: Alban Crequy <alban@xxxxxxxxxx>
Signed-off-by: Dongsu Park <dongsu@xxxxxxxxxx>
---
 include/linux/fs.h                |  1 +
 security/integrity/ima/ima_main.c | 15 +++++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 511fbaab..ced841ba 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2075,6 +2075,7 @@ struct file_system_type {
 #define FS_BINARY_MOUNTDATA	2
 #define FS_HAS_SUBTYPE		4
 #define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */
+#define FS_IMA_NO_CACHE		16	/* Force IMA to re-measure, re-appraise, re-audit files */
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
 	struct dentry *(*mount) (struct file_system_type *, int,
 		       const char *, void *);
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 6d78cb26..83edbad8 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -24,6 +24,7 @@
 #include <linux/slab.h>
 #include <linux/xattr.h>
 #include <linux/ima.h>
+#include <linux/fs.h>
 
 #include "ima.h"
 
@@ -228,9 +229,19 @@ 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 */
+	/*
+	 * Reset the measure, appraise and audit cached flags either if:
+	 * - ima_inode_setxattr was called, or
+	 * - based on filesystem feature flag
+	 * forcing the file to be re-evaluated.
+	 */
+	if (test_and_clear_bit(IMA_CHANGE_XATTR, &iint->atomic_flags)) {
 		iint->flags &= ~IMA_DONE_MASK;
+	} else if (inode->i_sb->s_type->fs_flags & FS_IMA_NO_CACHE) {
+		iint->flags &= ~IMA_DONE_MASK;
+		if (action & IMA_MEASURE)
+			iint->measured_pcrs = 0;
+	}
 
 	/* Determine if already appraised/measured based on bitmask
 	 * (IMA_MEASURE, IMA_MEASURED, IMA_XXXX_APPRAISE, IMA_XXXX_APPRAISED,
-- 
2.13.6