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Subject[PATCH] ima: define new policy condition based on the filesystem name
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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@redhat.com>
Signed-off-by: Mimi Zohar <zohar@linux.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
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