SELinux: Abstract use of file security blob

Don't use the file->f_security pointer directly.
Provide a helper function that provides the security blob pointer.
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

security/selinux/hooks.c

@@ -394,7 +394,7 @@ static int file_alloc_security(struct file *file)
 
 static void file_free_security(struct file *file)
 {
-	struct file_security_struct *fsec = file->f_security;
+	struct file_security_struct *fsec = selinux_file(file);
 	file->f_security = NULL;
 	kmem_cache_free(file_security_cache, fsec);
 }
@@ -1733,7 +1733,7 @@ static int file_has_perm(const struct cred *cred,
 			 struct file *file,
 			 u32 av)
 {
-	struct file_security_struct *fsec = file->f_security;
+	struct file_security_struct *fsec = selinux_file(file);
 	struct inode *inode = file_inode(file);
 	struct common_audit_data ad;
 	u32 sid = cred_sid(cred);
@@ -2077,7 +2077,7 @@ static int selinux_binder_transfer_file(struct task_struct *from,
 					struct file *file)
 {
 	u32 sid = task_sid(to);
-	struct file_security_struct *fsec = file->f_security;
+	struct file_security_struct *fsec = selinux_file(file);
 	struct dentry *dentry = file->f_path.dentry;
 	struct inode_security_struct *isec;
 	struct common_audit_data ad;
@@ -3323,7 +3323,7 @@ static int selinux_revalidate_file_permission(struct file *file, int mask)
 static int selinux_file_permission(struct file *file, int mask)
 {
 	struct inode *inode = file_inode(file);
-	struct file_security_struct *fsec = file->f_security;
+	struct file_security_struct *fsec = selinux_file(file);
 	struct inode_security_struct *isec;
 	u32 sid = current_sid();
 
@@ -3358,7 +3358,7 @@ static int ioctl_has_perm(const struct cred *cred, struct file *file,
 		u32 requested, u16 cmd)
 {
 	struct common_audit_data ad;
-	struct file_security_struct *fsec = file->f_security;
+	struct file_security_struct *fsec = selinux_file(file);
 	struct inode *inode = file_inode(file);
 	struct inode_security_struct *isec;
 	struct lsm_ioctlop_audit ioctl;
@@ -3610,7 +3610,7 @@ static void selinux_file_set_fowner(struct file *file)
 {
 	struct file_security_struct *fsec;
 
-	fsec = file->f_security;
+	fsec = selinux_file(file);
 	fsec->fown_sid = current_sid();
 }
 
@@ -3625,7 +3625,7 @@ static int selinux_file_send_sigiotask(struct task_struct *tsk,
 	/* struct fown_struct is never outside the context of a struct file */
 	file = container_of(fown, struct file, f_owner);
 
-	fsec = file->f_security;
+	fsec = selinux_file(file);
 
 	if (!signum)
 		perm = signal_to_av(SIGIO); /* as per send_sigio_to_task */
@@ -3649,7 +3649,7 @@ static int selinux_file_open(struct file *file)
 	struct file_security_struct *fsec;
 	struct inode_security_struct *isec;
 
-	fsec = file->f_security;
+	fsec = selinux_file(file);
 	isec = inode_security(file_inode(file));
 	/*
 	 * Save inode label and policy sequence number
@@ -3788,7 +3788,7 @@ static int selinux_kernel_module_from_file(struct file *file)
 	ad.type = LSM_AUDIT_DATA_FILE;
 	ad.u.file = file;
 
-	fsec = file->f_security;
+	fsec = selinux_file(file);
 	if (sid != fsec->sid) {
 		rc = avc_has_perm(&selinux_state,
 				  sid, fsec->sid, SECCLASS_FD, FD__USE, &ad);

security/selinux/include/objsec.h

@@ -165,4 +165,9 @@ static inline struct task_security_struct *selinux_cred(const struct cred *cred)
 	return cred->security + selinux_blob_sizes.lbs_cred;
 }
 
+static inline struct file_security_struct *selinux_file(const struct file *file)
+{
+	return file->f_security;
+}
+
 #endif /* _SELINUX_OBJSEC_H_ */