BACKPORT: binder: use cred instead of task for selinux checks

commit 52f88693378a58094c538662ba652aff0253c4fe upstream.

Since binder was integrated with selinux, it has passed
'struct task_struct' associated with the binder_proc
to represent the source and target of transactions.
The conversion of task to SID was then done in the hook
implementations. It turns out that there are race conditions
which can result in an incorrect security context being used.

Fix by using the 'struct cred' saved during binder_open and pass
it to the selinux subsystem.

Cc: stable@vger.kernel.org # 5.14 (need backport for earlier stables)
Fixes: 79af73079d75 ("Add security hooks to binder and implement the hooks for SELinux.")
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Todd Kjos <tkjos@google.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Change-Id: Id7157515d2b08f11683aeb8ad9b8f1da075d34e7
[tkjos@ Fixed minor conflicts]
Bug: 200688826
Signed-off-by: Todd Kjos <tkjos@google.com>

1 files changed, 16 insertions, 16 deletions

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index ec3a6bab29de..169f4be3ce56 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1121,22 +1121,22 @@
  *
  * @binder_set_context_mgr
  *	Check whether @mgr is allowed to be the binder context manager.
- *	@mgr contains the task_struct for the task being registered.
+ *	@mgr contains the struct cred for the current binder process.
  *	Return 0 if permission is granted.
  * @binder_transaction
  *	Check whether @from is allowed to invoke a binder transaction call
  *	to @to.
- *	@from contains the task_struct for the sending task.
- *	@to contains the task_struct for the receiving task.
- * @binder_transfer_binder
+ *	@from contains the struct cred for the sending process.
+ *	@to contains the struct cred for the receiving process.
+ * @binder_transfer_binder:
  *	Check whether @from is allowed to transfer a binder reference to @to.
- *	@from contains the task_struct for the sending task.
- *	@to contains the task_struct for the receiving task.
- * @binder_transfer_file
+ *	@from contains the struct cred for the sending process.
+ *	@to contains the struct cred for the receiving process.
+ * @binder_transfer_file:
  *	Check whether @from is allowed to transfer @file to @to.
- *	@from contains the task_struct for the sending task.
+ *	@from contains the struct cred for the sending process.
  *	@file contains the struct file being transferred.
- *	@to contains the task_struct for the receiving task.
+ *	@to contains the struct cred for the receiving process.
  *
  * @ptrace_access_check:
  *	Check permission before allowing the current process to trace the
@@ -1301,13 +1301,13 @@
  */
 
 union security_list_options {
-	int (*binder_set_context_mgr)(struct task_struct *mgr);
-	int (*binder_transaction)(struct task_struct *from,
-					struct task_struct *to);
-	int (*binder_transfer_binder)(struct task_struct *from,
-					struct task_struct *to);
-	int (*binder_transfer_file)(struct task_struct *from,
-					struct task_struct *to,
+	int (*binder_set_context_mgr)(const struct cred *mgr);
+	int (*binder_transaction)(const struct cred *from,
+					const struct cred *to);
+	int (*binder_transfer_binder)(const struct cred *from,
+					const struct cred *to);
+	int (*binder_transfer_file)(const struct cred *from,
+					const struct cred *to,
 					struct file *file);
 
 	int (*ptrace_access_check)(struct task_struct *child,