trigger NODATA error for invalid InRelease files

With the selfgrown splitting we got the problem of not recovering
from networks which just reply with invalid data like those sending
us login pages to authenticate with the network (e.g. hotels) back.

The good thing about the InRelease file is that we know that it must
be clearsigned (a Release file might or might not have a detached sig)
so if we get a file but are unable to split it something is seriously
wrong, so there is not much point in trying further.

The Acquire system already looks out for a NODATA error from gpgv,
so this adds a new error message sent to the acquire system in case
the splitting we do now ourselves failed including this magic word.

Closes: #712486

2 files changed, 13 insertions, 4 deletions

diff --git a/apt-pkg/contrib/gpgv.cc b/apt-pkg/contrib/gpgv.cc
index 31db7d5fe..f47e7ea48 100644
--- a/apt-pkg/contrib/gpgv.cc
+++ b/apt-pkg/contrib/gpgv.cc
@@ -154,7 +154,7 @@ void ExecGPGV(std::string const &File, std::string const &FileGPG,
 	 if (sigFd != -1)
 	    unlink(data);
 	 ioprintf(std::cerr, "Splitting up %s into data and signature failed", File.c_str());
-	 exit(EINTERNAL);
+	 exit(112);
       }
       Args.push_back(sig);
       Args.push_back(data);
diff --git a/apt-pkg/contrib/gpgv.h b/apt-pkg/contrib/gpgv.h
index 08b10a97a..45f069058 100644
--- a/apt-pkg/contrib/gpgv.h
+++ b/apt-pkg/contrib/gpgv.h
@@ -23,9 +23,18 @@
 /** \brief generates and run the command to verify a file with gpgv
  *
  * If File and FileSig specify the same file it is assumed that we
- * deal with a clear-signed message. In that case the file will be
- * rewritten to be in a good-known format without uneeded whitespaces
- * and additional messages (unsigned or signed).
+ * deal with a clear-signed message. Note that the method will accept
+ * and validate files which include additional (unsigned) messages
+ * without complaining. Do NOT open files accepted by this method
+ * for reading. Use #OpenMaybeClearSignedFile to access the message
+ * instead to ensure you are only reading signed data.
+ *
+ * The method does not return, but has some noteable exit-codes:
+ * 111 signals an internal error like the inability to execute gpgv,
+ * 112 indicates a clear-signed file which doesn't include a message,
+ *  which can happen if APT is run while on a network requiring
+ *  authentication before usage (e.g. in hotels)
+ * All other exit-codes are passed-through from gpgv.
  *
  * @param File is the message (unsigned or clear-signed)
  * @param FileSig is the signature (detached or clear-signed)