Fix endless loop in apt-get update that can cause disk fillup

The apt http code parses Content-Length and Content-Range. For
both requests the variable "Size" is used and the semantic for
this Size is the total file size. However Content-Length is not
the entire file size for partital file requests. For servers that
send the Content-Range header first and then the Content-Length
header this can lead to globbing of Size so that its less than
the real file size. This may lead to a subsequent passing of a
negative number into the CircleBuf which leads to a endless
loop that writes data.

Thanks to Anton Blanchard for the analysis and initial patch.

LP: #1445239

1 files changed, 1 insertions, 1 deletions

diff --git a/methods/http.cc b/methods/http.cc
index 1b996db98..ad90c9891 100644
--- a/methods/http.cc
+++ b/methods/http.cc
@@ -443,7 +443,7 @@ bool HttpServerState::RunData(FileFd * const File)
       else if (JunkSize != 0)
 	 In.Limit(JunkSize);
       else
-	 In.Limit(Size - StartPos);
+	 In.Limit(DownloadSize);
       
       // Just transfer the whole block.
       do