gpgv: Flush the files before checking for errors

This is a follow up to the previous issue where we did not check
if getline() returned -1 due to an end of file or due to an error
like memory allocation, treating both as end of file.

Here we ensure that we also handle buffered writes correctly by
flushing the files before checking for any errors in our error
stack.

Buffered writes themselves were introduced in 1.1.9, but the
function was never called with a buffered file from inside
apt until commit 46c4043d741cb2c1d54e7f5bfaa234f1b7580f6c
which was first released with apt 1.2.10. The function is
public, though, so fixing this is a good idea anyway.

Affected: >= 1.1.9
(cherry picked from commit 6212ee84a517ed68217429022bd45c108ecf9f85)
(cherry picked from commit e115da452632a024a2885fea27a6c2c5145282b1)

1 files changed, 6 insertions, 0 deletions

diff --git a/apt-pkg/contrib/gpgv.cc b/apt-pkg/contrib/gpgv.cc
index 7e7b3ac80..a5f2441b7 100644
--- a/apt-pkg/contrib/gpgv.cc
+++ b/apt-pkg/contrib/gpgv.cc
@@ -329,6 +329,12 @@ bool SplitClearSignedFile(std::string const &InFile, FileFd * const ContentFile,
    if (buf != NULL)
       free(buf);
 
+   // Flush the files. Errors will be checked below.
+   if (SignatureFile != nullptr)
+      SignatureFile->Flush();
+   if (ContentFile != nullptr)
+      ContentFile->Flush();
+
    // An error occured during reading - propagate it up
    bool const hasErrored = _error->PendingError();
    _error->MergeWithStack();