bpf: Plug a potential exclusive map memory leak

When excl_prog_hash is 0 and excl_prog_hash_size is non-zero, the map also
needs to be freed. Otherwise, the map memory will not be reclaimed, just
like the memory leak problem reported by syzbot [1].

syzbot reported:
BUG: memory leak
  backtrace (crc 7b9fb9b4):
    map_create+0x322/0x11e0 kernel/bpf/syscall.c:1512
    __sys_bpf+0x3556/0x3610 kernel/bpf/syscall.c:6131

Fixes: baefdbd ("bpf: Implement exclusive map creation")
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=cf08c551fecea9fd1320
Tested-by: [email protected]
Signed-off-by: Edward Adam Davis <[email protected]>
Acked-by: Yonghong Song <[email protected]>

Author: ea1davis

kernel/bpf/syscall.c

@@ -1586,7 +1586,8 @@ static int map_create(union bpf_attr *attr, bpfptr_t uattr)
 			goto free_map;
 		}
 	} else if (attr->excl_prog_hash_size) {
-		return -EINVAL;
+		err = -EINVAL;
+		goto free_map;
 	}
 
 	err = security_bpf_map_create(map, attr, token, uattr.is_kernel);