io_uring: use correct pointer for io_uring_show_cred()

Previous commit changed how we index the registered credentials, but
neglected to update one spot that is used when the personalities are
iterated through ->show_fdinfo(). Ensure we use the right struct type
for the iteration.

Reported-by: syzbot+a6d494688cdb797bdfce@syzkaller.appspotmail.com
Fixes: 1e6fa521 ("io_uring: COW io_identity on mismatch")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -8974,7 +8974,8 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 #ifdef CONFIG_PROC_FS
 static int io_uring_show_cred(int id, void *p, void *data)
 {
-	const struct cred *cred = p;
+	struct io_identity *iod = p;
+	const struct cred *cred = iod->creds;
 	struct seq_file *m = data;
 	struct user_namespace *uns = seq_user_ns(m);
 	struct group_info *gi;