tee: rewrite num_params access in tee_fetch_buf_data

Pointer to num_params field of the fetched structure is passed in a
separate function argument which provokes covscan complaints about
uninitialised accesses and also tingles my aliasing rules senses.
Rewrite to access it via the arg_struct argument which is fetched
earlier in the function flow.

* src/tee.c (TEE_FETCH_BUF_DATA): Change &arg_.num_params
to offsetof(typeof(arg_), num_params).
(tee_fetch_buf_data): Accept offset of the num_params field instead
of pointer to it; reconstruct the num_params pointer using it.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/tee.c b/src/tee.c
index f9eda5248..d7e9b15d9 100644
--- a/src/tee.c
+++ b/src/tee.c
@@ -33,7 +33,7 @@ struct tee_ioctl_shm_register_fd_data {
 
 #define TEE_FETCH_BUF_DATA(buf_, arg_, params_) \
 	tee_fetch_buf_data(tcp, arg, &buf_, sizeof(arg_), \
-			   &arg_, &arg_.num_params, \
+			   &arg_, offsetof(typeof(arg_), num_params), \
 			   params_)
 
 /* session id is printed as 0x%x in libteec */
@@ -56,7 +56,7 @@ tee_fetch_buf_data(struct tcb *const tcp,
 		   struct tee_ioctl_buf_data *buf,
 		   size_t arg_size,
 		   void *arg_struct,
-		   unsigned *num_params,
+		   size_t num_params_offs,
 		   uint64_t *params)
 {
 	if (umove_or_printaddr(tcp, arg, buf))
@@ -69,6 +69,7 @@ tee_fetch_buf_data(struct tcb *const tcp,
 		tee_print_buf(buf);
 		return RVAL_IOCTL_DECODED;
 	}
+	uint32_t *num_params = (uint32_t *) (arg_struct + num_params_offs);
 	if (entering(tcp) &&
 	    (arg_size + TEE_IOCTL_PARAM_SIZE(*num_params) != buf->buf_len)) {
 		/*