[PATCH 5.10 3/3] binder: use cred instead of task for getsecid

[Todd Kjos]

commit 4d5b5539742d2554591751b4248b0204d20dcc9d upstream.

Use the 'struct cred' saved at binder_open() to lookup
the security ID via security_cred_getsecid(). This
ensures that the security context that opened binder
is the one used to generate the secctx.

Cc: stable at vger.kernel.org # 5.4+
Fixes: ec74136ded79 ("binder: create node flag to request sender's security context")
Signed-off-by: Todd Kjos <tkjos at google.com>
Suggested-by: Stephen Smalley <stephen.smalley.work at gmail.com>
Reported-by: kernel test robot <lkp at intel.com>
Acked-by: Casey Schaufler <casey at schaufler-ca.com>
Signed-off-by: Paul Moore <paul at paul-moore.com>
Change-Id: Ia7b59804a0bdbd51191bbcca556414840307c623
---
 drivers/android/binder.c | 2 +-
 include/linux/security.h | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 50fff726dc70..3ba3944a9e1f 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -3103,7 +3103,7 @@ static void binder_transaction(struct binder_proc *proc,
 		u32 secid;
 		size_t added_size;
 
-		security_task_getsecid(proc->tsk, &secid);
+		security_cred_getsecid(proc->cred, &secid);
 		ret = security_secid_to_secctx(secid, &secctx, &secctx_sz);
 		if (ret) {
 			return_error = BR_FAILED_REPLY;
diff --git a/include/linux/security.h b/include/linux/security.h
index e67cc8c40865..35355429648e 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1003,6 +1003,11 @@ static inline void security_transfer_creds(struct cred *new,
 {
 }
 
+static inline void security_cred_getsecid(const struct cred *c, u32 *secid)
+{
+	*secid = 0;
+}
+
 static inline int security_kernel_act_as(struct cred *cred, u32 secid)
 {
 	return 0;
-- 
2.34.0.rc0.344.g81b53c2807-goog