binder: use cred instead of task for selinux checks

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>

1 files changed, 7 insertions, 7 deletions

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index b3c525353769..4c7ed0268ce3 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -26,13 +26,13 @@
  *   #undef LSM_HOOK
  * };
  */
-LSM_HOOK(int, 0, binder_set_context_mgr, struct task_struct *mgr)
-LSM_HOOK(int, 0, binder_transaction, struct task_struct *from,
-	 struct task_struct *to)
-LSM_HOOK(int, 0, binder_transfer_binder, struct task_struct *from,
-	 struct task_struct *to)
-LSM_HOOK(int, 0, binder_transfer_file, struct task_struct *from,
-	 struct task_struct *to, struct file *file)
+LSM_HOOK(int, 0, binder_set_context_mgr, const struct cred *mgr)
+LSM_HOOK(int, 0, binder_transaction, const struct cred *from,
+	 const struct cred *to)
+LSM_HOOK(int, 0, binder_transfer_binder, const struct cred *from,
+	 const struct cred *to)
+LSM_HOOK(int, 0, binder_transfer_file, const struct cred *from,
+	 const struct cred *to, struct file *file)
 LSM_HOOK(int, 0, ptrace_access_check, struct task_struct *child,
 	 unsigned int mode)
 LSM_HOOK(int, 0, ptrace_traceme, struct task_struct *parent)