linux-kernel - [PATCH] ima: define new policy condition based on the filesystem name

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Message-Id: <1516033236.6607.6.camel@linux.vnet.ibm.com>
Date:   Mon, 15 Jan 2018 11:20:36 -0500
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     linux-integrity <linux-integrity@...r.kernel.org>
Cc:     linux-security-module <linux-security-module@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Dongsu Park <dongsu@...volk.io>,
        Alban Crequy <alban@...volk.io>,
        Christoph Hellwig <hch@...radead.org>,
        Seth Forshee <seth.forshee@...onical.com>
Subject: [PATCH] ima: define new policy condition based on the filesystem
 name

Some filesystems do not export the filesystem's magic number, as it is
considered internal, private data.  In other cases, the policy rule
needs to identify a specifically mounted filesystem (eg. rootfs).

This patch defines a new IMA policy condition named "fsname", based on
the superblock's file_system_type (sb->s_type) name.

By defining a policy rule in terms of the filesystem magic number and
the superblock filesystem name, files on the rootfs filesystem are only
appraised, when rootfs is a tmpfs filesystem, which supports xattrs.

Sample rules:
measure func=FILE_CHECK fsname=xfs
appraise fsmagic=0x01021994 fsname=rootfs

Suggested-by: Dave Chinner <dchinner@...hat.com>
Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
---
 Documentation/ABI/testing/ima_policy |  2 +-
 security/integrity/ima/ima_policy.c  | 25 ++++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index b0e8143c681f..281b88d17a37 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -21,7 +21,7 @@ Description:
 			audit | hash | dont_hash
 		condition:= base | lsm  [option]
 			base:	[[func=] [mask=] [fsmagic=] [fsuuid=] [uid=]
-				[euid=] [fowner=]]
+				[euid=] [fowner=] [fsname=]]
 			lsm:	[[subj_user=] [subj_role=] [subj_type=]
 				 [obj_user=] [obj_role=] [obj_type=]]
 			option:	[[appraise_type=]] [permit_directio] [force]
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 878ae1a06e1e..ceffb98d79ca 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -33,6 +33,7 @@
 #define IMA_INMASK	0x0040
 #define IMA_EUID	0x0080
 #define IMA_PCR		0x0100
+#define IMA_FSNAME	0x0200
 
 #define UNKNOWN		0
 #define MEASURE		0x0001	/* same as IMA_MEASURE */
@@ -74,6 +75,7 @@ struct ima_rule_entry {
 		void *args_p;	/* audit value */
 		int type;	/* audit type */
 	} lsm[MAX_LSM_RULES];
+	char *fsname;
 };
 
 /*
@@ -267,6 +269,9 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
 	if ((rule->flags & IMA_FSMAGIC)
 	    && rule->fsmagic != inode->i_sb->s_magic)
 		return false;
+	if ((rule->flags & IMA_FSNAME)
+	    && strcmp(rule->fsname, inode->i_sb->s_type->name))
+		return false;
 	if ((rule->flags & IMA_FSUUID) &&
 	    !uuid_equal(&rule->fsuuid, &inode->i_sb->s_uuid))
 		return false;
@@ -528,7 +533,7 @@ enum {
 	Opt_audit, Opt_hash, Opt_dont_hash,
 	Opt_obj_user, Opt_obj_role, Opt_obj_type,
 	Opt_subj_user, Opt_subj_role, Opt_subj_type,
-	Opt_func, Opt_mask, Opt_fsmagic,
+	Opt_func, Opt_mask, Opt_fsmagic, Opt_fsname,
 	Opt_fsuuid, Opt_uid_eq, Opt_euid_eq, Opt_fowner_eq,
 	Opt_uid_gt, Opt_euid_gt, Opt_fowner_gt,
 	Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
@@ -553,6 +558,7 @@ static match_table_t policy_tokens = {
 	{Opt_func, "func=%s"},
 	{Opt_mask, "mask=%s"},
 	{Opt_fsmagic, "fsmagic=%s"},
+	{Opt_fsname, "fsname=%s"},
 	{Opt_fsuuid, "fsuuid=%s"},
 	{Opt_uid_eq, "uid=%s"},
 	{Opt_euid_eq, "euid=%s"},
@@ -763,6 +769,17 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 			if (!result)
 				entry->flags |= IMA_FSMAGIC;
 			break;
+		case Opt_fsname:
+			ima_log_string(ab, "fsname", args[0].from);
+
+			entry->fsname = kstrdup(args[0].from, GFP_KERNEL);
+			if (!entry->fsname) {
+				result = -ENOMEM;
+				break;
+			}
+			result = 0;
+			entry->flags |= IMA_FSNAME;
+			break;
 		case Opt_fsuuid:
 			ima_log_string(ab, "fsuuid", args[0].from);
 
@@ -1094,6 +1111,12 @@ int ima_policy_show(struct seq_file *m, void *v)
 		seq_puts(m, " ");
 	}
 
+	if (entry->flags & IMA_FSNAME) {
+		snprintf(tbuf, sizeof(tbuf), "%s", entry->fsname);
+		seq_printf(m, pt(Opt_fsname), tbuf);
+		seq_puts(m, " ");
+	}
+
 	if (entry->flags & IMA_PCR) {
 		snprintf(tbuf, sizeof(tbuf), "%d", entry->pcr);
 		seq_printf(m, pt(Opt_pcr), tbuf);
-- 
2.7.4