binder: use cred instead of task for getsecid

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@vger.kernel.org # 5.4+
Fixes: ec74136ded79 ("binder: create node flag to request sender's security context")
Signed-off-by: Todd Kjos <tkjos@google.com>
Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 1571e01cfa5286576a3ff140c87355a41fcba95f..49b08c04fa09a919de8b342b08f5e8c05e87e17f 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2713,16 +2713,7 @@ static void binder_transaction(struct binder_proc *proc,
                u32 secid;
                size_t added_size;
 
-               /*
-                * Arguably this should be the task's subjective LSM secid but
-                * we can't reliably access the subjective creds of a task
-                * other than our own so we must use the objective creds, which
-                * are safe to access.  The downside is that if a task is
-                * temporarily overriding it's creds it will not be reflected
-                * here; however, it isn't clear that binder would handle that
-                * case well anyway.
-                */
-               security_task_getsecid_obj(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 9be72166e85965e54de92419f74d310ba76e0bf5..cc6d393583368e38d6ed51dc414fe4dfa710abde 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1041,6 +1041,11 @@ 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;