promote filesize to a hashstring

It is a very simple hashstring, which is why it isn't contributing to
the usability of a list of them, but it is also trivial to check and
calculate, so it doesn't hurt checking it either as it can combined even
with the simplest other hashes greatly complicate attacks on them as you
suddenly need a same-size hash collision, which is usually a lot harder
to achieve.

2 files changed, 29 insertions, 7 deletions

diff --git a/apt-pkg/contrib/hashes.cc b/apt-pkg/contrib/hashes.cc
index 417982343..55180c642 100644
--- a/apt-pkg/contrib/hashes.cc
+++ b/apt-pkg/contrib/hashes.cc
@@ -29,7 +29,7 @@
 
 const char * HashString::_SupportedHashes[] =
 {
-   "SHA512", "SHA256", "SHA1", "MD5Sum", NULL
+   "SHA512", "SHA256", "SHA1", "MD5Sum", "Checksum-FileSize", NULL
 };
 
 HashString::HashString()
@@ -111,6 +111,8 @@ std::string HashString::GetHashForFile(std::string filename) const      /*{{{*/
       SHA512.AddFD(Fd);
       fileHash = (std::string)SHA512.Result();
    }
+   else if (strcasecmp(Type.c_str(), "Checksum-FileSize") == 0)
+      strprintf(fileHash, "%llu", Fd.FileSize());
    Fd.Close();
 
    return fileHash;
@@ -147,7 +149,13 @@ bool HashStringList::usable() const					/*{{{*/
       return false;
    std::string const forcedType = _config->Find("Acquire::ForceHash", "");
    if (forcedType.empty() == true)
-      return true;
+   {
+      // FileSize alone isn't usable
+      for (std::vector<HashString>::const_iterator hs = list.begin(); hs != list.end(); ++hs)
+	 if (hs->HashType() != "Checksum-FileSize")
+	    return true;
+      return false;
+   }
    return find(forcedType) != NULL;
 }
 									/*}}}*/
@@ -201,6 +209,9 @@ bool HashStringList::VerifyFile(std::string filename) const		/*{{{*/
    HashString const * const hs = find(NULL);
    if (hs == NULL || hs->VerifyFile(filename) == false)
       return false;
+   HashString const * const hsf = find("Checksum-FileSize");
+   if (hsf != NULL && hsf->VerifyFile(filename) == false)
+      return false;
    return true;
 }
 									/*}}}*/
@@ -235,6 +246,14 @@ bool HashStringList::operator!=(HashStringList const &other) const
 }
 									/*}}}*/
 
+// PrivateHashes							/*{{{*/
+class PrivateHashes {
+public:
+   unsigned long long FileSize;
+
+   PrivateHashes() : FileSize(0) {}
+};
+									/*}}}*/
 // Hashes::Add* - Add the contents of data or FD			/*{{{*/
 bool Hashes::Add(const unsigned char * const Data,unsigned long long const Size, unsigned int const Hashes)
 {
@@ -254,6 +273,7 @@ bool Hashes::Add(const unsigned char * const Data,unsigned long long const Size,
 #if __GNUC__ >= 4
 	#pragma GCC diagnostic pop
 #endif
+   d->FileSize += Size;
    return Res;
 }
 bool Hashes::AddFD(int const Fd,unsigned long long Size, unsigned int const Hashes)
@@ -314,15 +334,17 @@ HashStringList Hashes::GetHashStringList()
 #if __GNUC__ >= 4
 	#pragma GCC diagnostic pop
 #endif
+   std::string SizeStr;
+   strprintf(SizeStr, "%llu", d->FileSize);
+   hashes.push_back(HashString("Checksum-FileSize", SizeStr));
    return hashes;
 }
 #if __GNUC__ >= 4
 	#pragma GCC diagnostic push
 	#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
-	#pragma GCC diagnostic ignored "-Wsuggest-attribute=const"
 #endif
-Hashes::Hashes() {}
-Hashes::~Hashes() {}
+Hashes::Hashes() { d = new PrivateHashes(); }
+Hashes::~Hashes() { delete d; }
 #if __GNUC__ >= 4
 	#pragma GCC diagnostic pop
 #endif
diff --git a/apt-pkg/contrib/hashes.h b/apt-pkg/contrib/hashes.h
index caeba006d..e2e213855 100644
--- a/apt-pkg/contrib/hashes.h
+++ b/apt-pkg/contrib/hashes.h
@@ -161,10 +161,10 @@ class HashStringList
    std::vector<HashString> list;
 };
 
+class PrivateHashes;
 class Hashes
 {
-   /** \brief dpointer placeholder */
-   void *d;
+   PrivateHashes *d;
 
    public:
    /* those will disappear in the future as it is hard to add new ones this way.