[PATCH v15 11/26] ima: Define mac_admin_ns_capable() as a wrapper for ns_capable()

[Stefan Berger <stefanb@xxxxxxxxxxxxx>]

Define mac_admin_ns_capable() as a wrapper for the combined ns_capable()
checks on CAP_MAC_ADMIN and CAP_SYS_ADMIN in a user namespace. Return
true on the check if either capability or both are available.

Use mac_admin_ns_capable() in place of capable(SYS_ADMIN). This will allow
an IMA namespace to read the policy with only CAP_MAC_ADMIN, which has
less privileges than CAP_SYS_ADMIN.

Since CAP_MAC_ADMIN is an additional capability added to an existing gate
avoid auditing in case it is not set.

Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Signed-off-by: Denis Semakin <denis.semakin@xxxxxxxxxx>
Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>

---
v13:
  - implemented file_sb_user_ns(const struct file *); const is needed so it
    can be called with seq_file's 'const struct file *file'

v11:
  - use ns_capable_noaudit for CAP_MAC_ADMIN to avoid auditing in this case
---
 include/linux/capability.h      | 6 ++++++
 include/linux/fs.h              | 5 +++++
 security/integrity/ima/ima.h    | 6 ++++++
 security/integrity/ima/ima_fs.c | 5 ++++-
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 65efb74c3585..dc3e1230b365 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -270,6 +270,12 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
 		ns_capable(ns, CAP_SYS_ADMIN);
 }
 
+static inline bool mac_admin_ns_capable(struct user_namespace *ns)
+{
+	return ns_capable_noaudit(ns, CAP_MAC_ADMIN) ||
+		ns_capable(ns, CAP_SYS_ADMIN);
+}
+
 /* audit system wants to get cap info from files as well */
 int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
 			   const struct dentry *dentry,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c1769a2c5d70..4662efed3171 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2730,6 +2730,11 @@ static inline struct user_namespace *file_mnt_user_ns(struct file *file)
 	return mnt_user_ns(file->f_path.mnt);
 }
 
+static inline struct user_namespace *file_sb_user_ns(const struct file *file)
+{
+	return i_user_ns(file_inode(file));
+}
+
 static inline struct mnt_idmap *file_mnt_idmap(struct file *file)
 {
 	return mnt_idmap(file->f_path.mnt);
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 4de8ec776611..69f95ed0b8c6 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -492,4 +492,10 @@ static inline int ima_filter_rule_match(u32 secid, u32 field, u32 op,
 #define	POLICY_FILE_FLAGS	S_IWUSR
 #endif /* CONFIG_IMA_READ_POLICY */
 
+static inline
+struct user_namespace *ima_user_ns_from_file(const struct file *filp)
+{
+	return file_sb_user_ns(filp);
+}
+
 #endif /* __LINUX_IMA_H */
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 89d3113ceda1..c41aa61b7393 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -377,6 +377,9 @@ static const struct seq_operations ima_policy_seqops = {
  */
 static int ima_open_policy(struct inode *inode, struct file *filp)
 {
+#ifdef CONFIG_IMA_READ_POLICY
+	struct user_namespace *user_ns = ima_user_ns_from_file(filp);
+#endif
 	struct ima_namespace *ns = &init_ima_ns;
 
 	if (!(filp->f_flags & O_WRONLY)) {
@@ -385,7 +388,7 @@ static int ima_open_policy(struct inode *inode, struct file *filp)
 #else
 		if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
 			return -EACCES;
-		if (!capable(CAP_SYS_ADMIN))
+		if (!mac_admin_ns_capable(user_ns))
 			return -EPERM;
 		return seq_open(filp, &ima_policy_seqops);
 #endif
-- 
2.37.3