[RFC PATCH] ima: differentiate overlay, pivot_root, and other pathnames

[RFC PATCH] ima: differentiate overlay, pivot_root, and other pathnames

[Mimi Zohar]

Relative file pathnames are included in the IMA measurement list making
it difficult to differentiate files.  Permit replacing the relative
pathname with the (raw) full pathname in the measurement list.

Define a new module param named "ima.rawpath".

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
comment: this change does not address the simple "unshare -m" case
without pivot_root.

 .../admin-guide/kernel-parameters.txt          |  7 +++++++
 security/integrity/ima/ima_api.c               | 18 +++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91ba391f9b32..d49a5edcd3c3 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1890,6 +1890,13 @@
 			different crypto accelerators. This option can be used
 			to achieve best performance for particular HW.
 
+	ima.rawpath=	[IMA]
+			Format: <bool>
+			Default: 0
+			This parameter controls whether the IMA measurement
+			list contains the relative or raw full file pathnames
+			in the IMA measurement list.
+
 	init=		[KNL]
 			Format: <full_path>
 			Run specified binary instead of /sbin/init as init
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index a64fb0130b01..42c6ff7056e6 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -9,14 +9,19 @@
  *	appraise_measurement, store_measurement and store_template.
  */
 #include <linux/slab.h>
+#include <linux/moduleparam.h>
 #include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/fs_struct.h>
 #include <linux/xattr.h>
 #include <linux/evm.h>
 #include <linux/iversion.h>
 
 #include "ima.h"
 
+static bool rawpath_enabled;
+module_param_named(rawpath, rawpath_enabled, bool, 0);
+
 /*
  * ima_free_template_entry - free an existing template entry
  */
@@ -390,11 +395,22 @@ void ima_audit_measurement(struct integrity_iint_cache *iint,
  */
 const char *ima_d_path(const struct path *path, char **pathbuf, char *namebuf)
 {
+	struct dentry *dentry = NULL;
 	char *pathname = NULL;
 
 	*pathbuf = __getname();
 	if (*pathbuf) {
-		pathname = d_absolute_path(path, *pathbuf, PATH_MAX);
+		if (!rawpath_enabled) {
+			pathname = d_absolute_path(path, *pathbuf, PATH_MAX);
+		} else {
+			/* Use union/overlay full pathname */
+			if (unlikely(path->dentry->d_flags & DCACHE_OP_REAL))
+				dentry = d_real(path->dentry, NULL);
+			else
+				dentry = path->dentry;
+			pathname = dentry_path_raw(dentry, *pathbuf, PATH_MAX);
+		}
+
 		if (IS_ERR(pathname)) {
 			__putname(*pathbuf);
 			*pathbuf = NULL;
-- 
2.27.0

Re: [RFC PATCH] ima: differentiate overlay, pivot_root, and other pathnames

[Mimi Zohar]

On Wed, 2021-11-10 at 10:28 -0500, Michael Peters wrote:

> This looks good, but would be even better if the flag that controlled
> this was settable in the ima_policy. That's much easier to work with
> in a lot of DevOps toolchains and pipelines and is similar to how the
> other ima configuration is done.

Thanks, Michael.  Agreed, which is one of the reasons for posting this
patch as an RFC.  The other reason is that it is an incomplete
solution, since it doesn't address mount namespaces.  Any suggestions
for addressing mount namespaces would be appreciated. Assuming there is
a benefit for a partial solution, I'll add the per policy rule support.

thanks,

Mimi