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Bug 1486711 - Fill logically uninitialized parts of an XPCOM string's buffer with a marker byte in debug builds. r=froydnj

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MozReview-Commit-ID: IwLikJpacAW

Differential Revision: https://phabricator.services.mozilla.com/D4657

--HG--
extra : moz-landing-system : lando
This commit is contained in:
Henri Sivonen 2018-09-07 05:47:57 +00:00
parent 434c47b3cb
commit 1a38ec4710
3 changed files with 63 additions and 0 deletions
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14
servo/support/gecko/nsstring/src/lib.rs
View File

@ -452,6 +452,20 @@ macro_rules! define_string_types {
let mut this = self.string.as_repr();
this.as_mut().length = length as u32;
*(this.as_mut().data.as_ptr().offset(length as isize)) = 0;
if cfg!(debug_assertions) {
// Overwrite the unused part in debug builds. Note
// that capacity doesn't include space for the zero
// terminator, so starting after the zero-terminator
// we wrote ends up overwriting the terminator space
// not reflected in the capacity number.
// write_bytes() takes care of multiplying the length
// by the size of T.
ptr::write_bytes(this.as_mut().data.as_ptr().offset((length + 1) as isize),
0xE4u8,
self.capacity - length);
}
// We don't have a Rust interface for mozilla/MemoryChecking.h,
// so let's just not communicate with MSan/Valgrind here.
}
mem::forget(self); // Don't run the failure path in drop()
BulkWriteOk{}

17
xpcom/string/nsCharTraits.h
View File

@ -9,6 +9,7 @@
#include <ctype.h> // for |EOF|, |WEOF|
#include <string.h> // for |memcpy|, et al
#include "mozilla/MemoryChecking.h"
// This file may be used (through nsUTF8Utils.h) from non-XPCOM code, in
// particular the standalone software updater. In that case stub out
@ -148,6 +149,14 @@ struct nsCharTraits<char16_t>
aN * sizeof(char_type)));
}
static void uninitialize(char_type* aStr, size_t aN)
{
#ifdef DEBUG
memset(aStr, 0xE4, aN * sizeof(char_type));
#endif
MOZ_MAKE_MEM_UNDEFINED(aStr, aN * sizeof(char_type));
}
static char_type*
copyASCII(char_type* aStr1, const char* aStr2, size_t aN)
{
@ -356,6 +365,14 @@ struct nsCharTraits<char>
aN * sizeof(char_type)));
}
static void uninitialize(char_type* aStr, size_t aN)
{
#ifdef DEBUG
memset(aStr, 0xE4, aN * sizeof(char_type));
#endif
MOZ_MAKE_MEM_UNDEFINED(aStr, aN * sizeof(char_type));
}
static char_type*
copyASCII(char_type* aStr1, const char* aStr2, size_t aN)
{

32
xpcom/string/nsTSubstring.cpp
View File

@ -127,6 +127,16 @@ nsTSubstring<T>::StartBulkWriteImpl(size_type aCapacity,
char_traits::move(this->mData + aNewSuffixStart,
this->mData + aOldSuffixStart,
aSuffixLength);
if (aSuffixLength) {
char_traits::uninitialize(this->mData + aPrefixToPreserve,
aNewSuffixStart - aPrefixToPreserve);
char_traits::uninitialize(this->mData + aNewSuffixStart + aSuffixLength,
curCapacity + 1 - aNewSuffixStart -
aSuffixLength);
} else {
char_traits::uninitialize(this->mData + aPrefixToPreserve,
curCapacity + 1 - aPrefixToPreserve);
}
return curCapacity;
}
}
@ -224,6 +234,16 @@ nsTSubstring<T>::StartBulkWriteImpl(size_type aCapacity,
if (oldData == newData) {
char_traits::move(
newData + aNewSuffixStart, oldData + aOldSuffixStart, aSuffixLength);
if (aSuffixLength) {
char_traits::uninitialize(this->mData + aPrefixToPreserve,
aNewSuffixStart - aPrefixToPreserve);
char_traits::uninitialize(this->mData + aNewSuffixStart + aSuffixLength,
newCapacity + 1 - aNewSuffixStart -
aSuffixLength);
} else {
char_traits::uninitialize(this->mData + aPrefixToPreserve,
newCapacity + 1 - aPrefixToPreserve);
}
} else {
char_traits::copy(newData, oldData, aPrefixToPreserve);
char_traits::copy(
@ -242,6 +262,18 @@ nsTSubstring<T>::FinishBulkWriteImpl(size_type aLength)
if (aLength) {
this->mData[aLength] = char_type(0);
this->mLength = aLength;
#ifdef DEBUG
// ifdefed in order to avoid the call to Capacity() in non-debug
// builds.
//
// Our string is mutable, so Capacity() doesn't return zero.
// Capacity() doesn't include the space for the zero terminator,
// but we want to unitialize that slot, too. Since we start
// counting after the zero terminator the we just wrote above,
// we end up overwriting the space for terminator not reflected
// in the capacity number.
char_traits::uninitialize(this->mData + aLength + 1, Capacity() - aLength);
#endif
} else {
::ReleaseData(this->mData, this->mDataFlags);
SetToEmptyBuffer();