[RFC PATCH 2/4] ima: define new ima_sb_post_new_mount hook

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

IMA measures a file, verifies a file's integrity, and caches the
results.  On filesystems with MS_I_VERSION enabled, IMA can detect
file changes and cause them to be re-measured and verified.  On
filesystems without MS_I_VERSION enabled, files are measured and
verified just once.

This patch logs filesystems mounted without MS_I_VERSION.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
---
 include/linux/ima.h               |  5 +++++
 security/integrity/ima/ima_main.c | 44 +++++++++++++++++++++++++++++++++++++++
 security/security.c               |  1 +
 3 files changed, 50 insertions(+)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 0e4647e0eb60..4475cb01149c 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -23,6 +23,8 @@ extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
 extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
 			      enum kernel_read_file_id id);
 extern void ima_post_path_mknod(struct dentry *dentry);
+extern void ima_sb_post_new_mount(const struct vfsmount *newmnt,
+				  const struct path *path);
 
 #ifdef CONFIG_IMA_KEXEC
 extern void ima_add_kexec_buffer(struct kimage *image);
@@ -65,6 +67,9 @@ static inline void ima_post_path_mknod(struct dentry *dentry)
 	return;
 }
 
+static inline void ima_sb_post_new_mount(const struct vfsmount *newmnt,
+					 const struct path *path)
+{ }
 #endif /* CONFIG_IMA */
 
 #ifndef CONFIG_IMA_KEXEC
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index b00186914df8..a0a685189001 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -354,6 +354,50 @@ void ima_post_path_mknod(struct dentry *dentry)
 }
 
 /**
+ * ima_sb_post_new_mount - check filesystem mounted flags
+ *
+ * Indicate that filesystem isn't mounted with i_version enabled.
+ */
+void ima_sb_post_new_mount(const struct vfsmount *newmnt,
+			   const struct path *path)
+{
+	struct super_block *sb;
+	unsigned long pseudo_fs[] = {CGROUP_SUPER_MAGIC, CGROUP2_SUPER_MAGIC,
+		SYSFS_MAGIC, DEVPTS_SUPER_MAGIC, PSTOREFS_MAGIC, EFIVARFS_MAGIC,
+		DEBUGFS_MAGIC, TMPFS_MAGIC};
+	char *pathbuf = NULL;
+	char filename[NAME_MAX];
+	const char *pathname;
+	bool found = 0;
+	int i;
+
+	sb = newmnt ? newmnt->mnt_sb : path->mnt->mnt_sb;
+
+	if ((sb->s_flags & MS_I_VERSION) || (sb->s_flags & MS_RDONLY) ||
+	    (sb->s_flags & MS_KERNMOUNT))
+		return;
+
+	for (i = 0; i < ARRAY_SIZE(pseudo_fs); i++) {
+		if (pseudo_fs[i] != sb->s_magic)
+			continue;
+
+		found = 1;
+		break;
+	}
+	if (found)
+		return;
+
+	pathname = ima_d_path(path, &pathbuf, filename);
+	if (!pathname)
+		return;
+
+	if (newmnt)
+		pr_warn("ima: %s mounted without i_version enabled\n",
+			pathname);
+	 __putname(pathbuf);
+}
+
+/**
  * ima_read_file - pre-measure/appraise hook decision based on policy
  * @file: pointer to the file to be measured/appraised/audit
  * @read_id: caller identifier
diff --git a/security/security.c b/security/security.c
index 592153e8d2b6..79111141b383 100644
--- a/security/security.c
+++ b/security/security.c
@@ -402,6 +402,7 @@ void security_sb_post_new_mount(const struct vfsmount *newmnt,
 				const struct path *path)
 {
 	call_void_hook(sb_post_new_mount, newmnt, path);
+	ima_sb_post_new_mount(newmnt, path);
 }
 
 int security_sb_umount(struct vfsmount *mnt, int flags)
-- 
2.7.4