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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 22 insertions, 28 deletions

diff --git a/security/security.c b/security/security.c
index 1c696bce8e1c..a864ff824dd3 100644
--- a/security/security.c
+++ b/security/security.c
@@ -723,25 +723,25 @@ static void __init lsm_early_task(struct task_struct *task)
 
 /* Security operations */
 
-int security_binder_set_context_mgr(struct task_struct *mgr)
+int security_binder_set_context_mgr(const struct cred *mgr)
 {
 	return call_int_hook(binder_set_context_mgr, 0, mgr);
 }
 
-int security_binder_transaction(struct task_struct *from,
-				struct task_struct *to)
+int security_binder_transaction(const struct cred *from,
+				const struct cred *to)
 {
 	return call_int_hook(binder_transaction, 0, from, to);
 }
 
-int security_binder_transfer_binder(struct task_struct *from,
-				    struct task_struct *to)
+int security_binder_transfer_binder(const struct cred *from,
+				    const struct cred *to)
 {
 	return call_int_hook(binder_transfer_binder, 0, from, to);
 }
 
-int security_binder_transfer_file(struct task_struct *from,
-				  struct task_struct *to, struct file *file)
+int security_binder_transfer_file(const struct cred *from,
+				  const struct cred *to, struct file *file)
 {
 	return call_int_hook(binder_transfer_file, 0, from, to, file);
 }
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 227eb8967963..f32026bc96b4 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2004,22 +2004,19 @@ static inline u32 open_file_to_av(struct file *file)
 
 /* Hook functions begin here. */
 
-static int selinux_binder_set_context_mgr(struct task_struct *mgr)
+static int selinux_binder_set_context_mgr(const struct cred *mgr)
 {
-	u32 mysid = current_sid();
-	u32 mgrsid = task_sid(mgr);
-
 	return avc_has_perm(&selinux_state,
-			    mysid, mgrsid, SECCLASS_BINDER,
+			    current_sid(), cred_sid(mgr), SECCLASS_BINDER,
 			    BINDER__SET_CONTEXT_MGR, NULL);
 }
 
-static int selinux_binder_transaction(struct task_struct *from,
-				      struct task_struct *to)
+static int selinux_binder_transaction(const struct cred *from,
+				      const struct cred *to)
 {
 	u32 mysid = current_sid();
-	u32 fromsid = task_sid(from);
-	u32 tosid = task_sid(to);
+	u32 fromsid = cred_sid(from);
+	u32 tosid = cred_sid(to);
 	int rc;
 
 	if (mysid != fromsid) {
@@ -2030,27 +2027,24 @@ static int selinux_binder_transaction(struct task_struct *from,
 			return rc;
 	}
 
-	return avc_has_perm(&selinux_state,
-			    fromsid, tosid, SECCLASS_BINDER, BINDER__CALL,
-			    NULL);
+	return avc_has_perm(&selinux_state, fromsid, tosid,
+			    SECCLASS_BINDER, BINDER__CALL, NULL);
 }
 
-static int selinux_binder_transfer_binder(struct task_struct *from,
-					  struct task_struct *to)
+static int selinux_binder_transfer_binder(const struct cred *from,
+					  const struct cred *to)
 {
-	u32 fromsid = task_sid(from);
-	u32 tosid = task_sid(to);
-
 	return avc_has_perm(&selinux_state,
-			    fromsid, tosid, SECCLASS_BINDER, BINDER__TRANSFER,
+			    cred_sid(from), cred_sid(to),
+			    SECCLASS_BINDER, BINDER__TRANSFER,
 			    NULL);
 }
 
-static int selinux_binder_transfer_file(struct task_struct *from,
-					struct task_struct *to,
+static int selinux_binder_transfer_file(const struct cred *from,
+					const struct cred *to,
 					struct file *file)
 {
-	u32 sid = task_sid(to);
+	u32 sid = cred_sid(to);
 	struct file_security_struct *fsec = selinux_file(file);
 	struct dentry *dentry = file->f_path.dentry;
 	struct inode_security_struct *isec;