From fa126effc2a03e22708960344e62fc21259deb23 Mon Sep 17 00:00:00 2001 From: "Wladimir J. van der Laan" Date: Thu, 5 Jun 2014 10:10:52 +0200 Subject: [PATCH] Avoid undefined behavior using CFlatData in CScript serialization `&vch[vch.size()]` and even `&vch[0]` on vectors can cause assertion errors with VC in debug mode. This is the problem mentioned in #4239. The deeper problem with this is that we rely on undefined behavior. - Add `begin_ptr` and `end_ptr` functions that get the beginning and end pointer of vector in a reliable way that copes with empty vectors and doesn't reference outside the vector (see https://stackoverflow.com/questions/1339470/how-to-get-the-address-of-the-stdvector-buffer-start-most-elegantly/1339767#1339767). - Add a convenience constructor to CFlatData that wraps a vector. I added `begin_ptr` and `end_ptr` as separate functions as I imagine they will be useful in more places. --- src/script.h | 8 ++++---- src/serialize.h | 34 ++++++++++++++++++++++++++++++++++ 2 files changed, 38 insertions(+), 4 deletions(-) diff --git a/src/script.h b/src/script.h index bd6574627..ea988f0e4 100644 --- a/src/script.h +++ b/src/script.h @@ -770,12 +770,12 @@ public: void Serialize(Stream &s, int nType, int nVersion) const { std::vector compr; if (Compress(compr)) { - s << CFlatData(&compr[0], &compr[compr.size()]); + s << CFlatData(compr); return; } unsigned int nSize = script.size() + nSpecialScripts; s << VARINT(nSize); - s << CFlatData(&script[0], &script[script.size()]); + s << CFlatData(script); } template @@ -784,13 +784,13 @@ public: s >> VARINT(nSize); if (nSize < nSpecialScripts) { std::vector vch(GetSpecialSize(nSize), 0x00); - s >> REF(CFlatData(&vch[0], &vch[vch.size()])); + s >> REF(CFlatData(vch)); Decompress(nSize, vch); return; } nSize -= nSpecialScripts; script.resize(nSize); - s >> REF(CFlatData(&script[0], &script[script.size()])); + s >> REF(CFlatData(script)); } }; diff --git a/src/serialize.h b/src/serialize.h index 134174659..5ac85554c 100644 --- a/src/serialize.h +++ b/src/serialize.h @@ -37,6 +37,34 @@ inline T& REF(const T& val) return const_cast(val); } +/** Get begin pointer of vector (non-const version). + * @note These functions avoid the undefined case of indexing into an empty + * vector, as well as that of indexing after the end of the vector. + */ +template +inline T* begin_ptr(std::vector& v) +{ + return v.empty() ? NULL : &v[0]; +} +/** Get begin pointer of vector (const version) */ +template +inline const T* begin_ptr(const std::vector& v) +{ + return v.empty() ? NULL : &v[0]; +} +/** Get end pointer of vector (non-const version) */ +template +inline T* end_ptr(std::vector& v) +{ + return v.empty() ? NULL : (&v[0] + v.size()); +} +/** Get end pointer of vector (const version) */ +template +inline const T* end_ptr(const std::vector& v) +{ + return v.empty() ? NULL : (&v[0] + v.size()); +} + ///////////////////////////////////////////////////////////////// // // Templates for serializing to anything that looks like a stream, @@ -318,6 +346,12 @@ protected: char* pend; public: CFlatData(void* pbeginIn, void* pendIn) : pbegin((char*)pbeginIn), pend((char*)pendIn) { } + template + explicit CFlatData(std::vector &v) + { + pbegin = (char*)begin_ptr(v); + pend = (char*)end_ptr(v); + } char* begin() { return pbegin; } const char* begin() const { return pbegin; } char* end() { return pend; }