Address challenge feedback from Discord

Author: zardus

challenges/computing-101/DESCRIPTION.md

@@ -15,3 +15,7 @@ If you have questions, comments, feedback, and so on, join us on [the Discord ch
 **NOTE:**
 If you are looking for the old Assembly Crash Course, it has [been archived](https://pwn.college/archive/assembly-crash-course).
 Computing 101 is the current path through that material, with the concepts split across the modules below.
+
+**NOTE:**
+Computing 101 is foundational welcome material, not a belt checkpoint.
+Later belt dojos assume these machine-code and assembly skills, so learners with prior experience can skip around, and this is the place to return when those assumptions feel shaky.

challenges/computing-101/building-a-web-server/common/run.py

@@ -317,6 +317,10 @@ def retry_session():
     return session
 
 
+def request_failure(method, exc):
+    return f"{method}: Failed to connect ({type(exc).__name__}: {exc})"
+
+
 def random_data():
     return ''.join(random.choices(string.ascii_letters + string.digits,
                                   k=random.randrange(32, 256))).encode()
@@ -334,8 +338,8 @@ def validate_connect():
     session = retry_session()
     try:
         session.get("http://localhost", timeout=1)
-    except requests.exceptions.ConnectionError:
-        return "Connect: Failed to connect"
+    except requests.exceptions.RequestException as e:
+        return request_failure("Connect", e)
 
 
 def validate_get(data=None):
@@ -347,8 +351,8 @@ def validate_get(data=None):
         f.flush()
         try:
             response = session.get("http://localhost" + f.name, timeout=1)
-        except requests.exceptions.ConnectionError:
-            return "GET: Failed to connect"
+        except requests.exceptions.RequestException as e:
+            return request_failure("GET", e)
         if response.text.encode() != data:
             return "GET: File contents not correct"
 
@@ -361,8 +365,8 @@ def validate_post(data=None):
         pass
     try:
         session.post("http://localhost" + f.name, data=data, timeout=1)
-    except requests.exceptions.ConnectionError:
-        return "POST: Failed to connect"
+    except requests.exceptions.RequestException as e:
+        return request_failure("POST", e)
     try:
         if open(f.name, "rb").read() != data:
             return "POST: File contents not correct"
@@ -461,19 +465,30 @@ def target():
                     "-e", "inject=brk:signal=SIGKILL",
                     results_dir=results_dir,
                     timeout=timeout) as results:
-            for operation in operations:
-                print(f"Performing operation: {operation_names[operation]}")
+            for operation_index, operation in enumerate(operations, 1):
+                operation_name = operation_names[operation]
+                operation_label = f"operation {operation_index}/{len(operations)} ({operation_name})"
+                print(f"Performing {operation_label}")
                 try:
                     error = operation()
                     if error:
-                        errors.append(error)
+                        errors.append(f"{operation_label}: {error}")
                 except Exception as e:
-                    errors.append(f"Exception: {str(e)}")
+                    errors.append(f"{operation_label}: Exception ({type(e).__name__}: {e})")
         print()
 
         strace_errors = validate_strace(level, results, requirements)
         errors.extend(strace_errors)
 
+        request_operations = [op for op in operations if op in (validate_get, validate_post)]
+        connection_failures = [e for e in errors if "Failed to connect" in e]
+        if level >= 9 and request_operations and len(connection_failures) >= len(request_operations):
+            errors.append(
+                "Every checked HTTP request failed to connect. "
+                "For the concurrent levels, the parent should keep accepting after fork, "
+                "while each child handles one accepted client and exits."
+            )
+
         print("===== Result =====")
         if not errors:
             print("[✓] Success")

challenges/computing-101/common/builder

@@ -3,6 +3,7 @@
 import os
 os.environ["PATH"] = "/challenge/bin:/bin:/usr/bin:/usr/local/bin"
 
+import logging
 import pwnlib.context
 import pwnlib.asm
 import pwnlib.elf
@@ -14,6 +15,7 @@ import magic
 import sys
 
 pwnlib.context.context.arch = "amd64"
+logging.getLogger("pwnlib").setLevel(logging.ERROR)
 cs = capstone.Cs(capstone.CS_ARCH_X86, capstone.CS_MODE_64)
 
 

challenges/computing-101/control-flow/switch/DESCRIPTION.md

@@ -27,6 +27,10 @@ In this way, the program implements conditional logic _without any conditional c
 This challenge (at `/challenge/reverse-me`) has 256 possible cases, with only one of them (corresponding to an alphanumeric character) being different than the others.
 Look at the jump table (you'll have to look at a lot of entries...), look at the program to understand how to influence the index, and get the flag!
 
+`/challenge/reverse-me` is generated without source-level debug information, so gdb may say that it has no debugging symbols.
+That is expected: use gdb for disassembly and memory inspection, not for source-level debugging.
+As in the previous challenge, use gdb to understand the binary, then run `/challenge/reverse-me` directly with the recovered byte to get the flag.
+
 ----
 **NOTE:**
 Though you should look at the disassembly using `objdump -d -M intel /challenge/reverse-me`, objdump will try to interpret the jump table data as assembly instructions, which will result in garbage.
@@ -70,4 +74,3 @@ The output will be long, but it starts like this:
 The number after `x/` is how many entries gdb should print.
 Since the input byte chooses one of 256 entries, and each entry is one 8-byte code address, this lets you scan the table for the one address that differs.
 If gdb prints multiple entries on one line, the address on the left is the first entry on that line; the next entry is 8 bytes later.
-As in the previous challenge, use gdb to understand the binary, then run `/challenge/reverse-me` directly with the recovered byte to get the flag.

challenges/computing-101/numbers-as-strings/itoa-digit/challenge/.py/chal.py

@@ -14,7 +14,7 @@ def run_one(so_path, value, *, quiet):
         p = subprocess.run(
             ["/challenge/harness", so_path, str(value)],
             stdout=subprocess.PIPE,
-            stderr=(subprocess.DEVNULL if quiet else None),
+            stderr=subprocess.PIPE,
             timeout=5,
         )
     except subprocess.TimeoutExpired:
@@ -23,7 +23,9 @@ def run_one(so_path, value, *, quiet):
             "A function has to reach a `ret`; an accidental loop with no way out spins forever."
         )
     if p.returncode != 0:
-        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.")
+        stderr = p.stderr.decode("utf-8", errors="replace").strip()
+        details = f"\n\nHarness stderr:\n{stderr}" if stderr else ""
+        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.{details}")
     if len(p.stdout) < 8:
         raise AssertionError("The harness never reported a result --- did your itoa_digit crash?")
     return int.from_bytes(p.stdout[-8:], "little")

challenges/computing-101/numbers-as-strings/itoa-minimal/challenge/.py/chal.py

@@ -15,7 +15,7 @@ def run_one(so_path, value, *, quiet):
         p = subprocess.run(
             ["/challenge/harness", so_path, str(value)],
             stdout=subprocess.PIPE,
-            stderr=(subprocess.DEVNULL if quiet else None),
+            stderr=subprocess.PIPE,
             timeout=5,
         )
     except subprocess.TimeoutExpired:
@@ -24,7 +24,9 @@ def run_one(so_path, value, *, quiet):
             "A function has to reach a `ret`; an accidental loop with no way out spins forever."
         )
     if p.returncode != 0:
-        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.")
+        stderr = p.stderr.decode("utf-8", errors="replace").strip()
+        details = f"\n\nHarness stderr:\n{stderr}" if stderr else ""
+        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.{details}")
     return p.stdout
 
 

challenges/computing-101/numbers-as-strings/itoa-negative/challenge/.py/chal.py

@@ -18,7 +18,7 @@ def run_one(so_path, value, *, quiet):
         p = subprocess.run(
             ["/challenge/harness", so_path, str(value)],
             stdout=subprocess.PIPE,
-            stderr=(subprocess.DEVNULL if quiet else None),
+            stderr=subprocess.PIPE,
             timeout=5,
         )
     except subprocess.TimeoutExpired:
@@ -27,7 +27,9 @@ def run_one(so_path, value, *, quiet):
             "If the divide loop doesn't shrink the value toward 0 each pass, it spins forever."
         )
     if p.returncode != 0:
-        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.")
+        stderr = p.stderr.decode("utf-8", errors="replace").strip()
+        details = f"\n\nHarness stderr:\n{stderr}" if stderr else ""
+        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.{details}")
     return p.stdout
 
 

challenges/computing-101/numbers-as-strings/itoa-two-digits/challenge/.py/chal.py

@@ -15,7 +15,7 @@ def run_one(so_path, value, *, quiet):
         p = subprocess.run(
             ["/challenge/harness", so_path, str(value)],
             stdout=subprocess.PIPE,
-            stderr=(subprocess.DEVNULL if quiet else None),
+            stderr=subprocess.PIPE,
             timeout=5,
         )
     except subprocess.TimeoutExpired:
@@ -24,7 +24,9 @@ def run_one(so_path, value, *, quiet):
             "A function has to reach a `ret`; an accidental loop with no way out spins forever."
         )
     if p.returncode != 0:
-        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.")
+        stderr = p.stderr.decode("utf-8", errors="replace").strip()
+        details = f"\n\nHarness stderr:\n{stderr}" if stderr else ""
+        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.{details}")
     return p.stdout
 
 

challenges/computing-101/numbers-as-strings/itoa/challenge/.py/chal.py

@@ -15,7 +15,7 @@ def run_one(so_path, value, *, quiet):
         p = subprocess.run(
             ["/challenge/harness", so_path, str(value)],
             stdout=subprocess.PIPE,
-            stderr=(subprocess.DEVNULL if quiet else None),
+            stderr=subprocess.PIPE,
             timeout=5,
         )
     except subprocess.TimeoutExpired:
@@ -24,7 +24,9 @@ def run_one(so_path, value, *, quiet):
             "If the divide loop doesn't shrink the value toward 0 each pass, it spins forever."
         )
     if p.returncode != 0:
-        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.")
+        stderr = p.stderr.decode("utf-8", errors="replace").strip()
+        details = f"\n\nHarness stderr:\n{stderr}" if stderr else ""
+        raise AssertionError(f"The harness exited abnormally (status {p.returncode}) on value {value}.{details}")
     return p.stdout
 
 

challenges/computing-101/the-stack-revisited/mem-envp/DESCRIPTION.md

@@ -39,3 +39,12 @@ Two new things to notice:
 
 In this challenge, we will set the `FLAG` environment variable to the actual flag and run your program with no arguments and no other env vars.
 That means `[rsp+24]` will hold a pointer to the `FLAG=...` string, and you can get the flag by `write()`ing it out!
+
+This is a whole-program level, so submit an executable, not a shared library.
+Assemble and link your program, then pass that executable to the checker:
+
+```console
+hacker@dojo:~$ as -o envp.o envp.s
+hacker@dojo:~$ ld -o envp envp.o
+hacker@dojo:~$ /challenge/check envp
+```