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CoreFoundation: correct alignment mis-assumption #3164

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Apr 1, 2022
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CoreFoundation: correct alignment mis-assumption #3164

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16 changes: 15 additions & 1 deletion CoreFoundation/Base.subproj/CFRuntime.c
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Original file line number Diff line number Diff line change
Expand Up @@ -442,7 +442,21 @@ CFTypeRef _CFRuntimeCreateInstance(CFAllocatorRef allocator, CFTypeID typeID, CF
uintptr_t isa = __CFRuntimeObjCClassTable[typeID];
CFIndex size = sizeof(CFRuntimeBase) + extraBytes;
const CFRuntimeClass *cls = __CFRuntimeClassTable[typeID];
size_t align = (cls->version & _kCFRuntimeRequiresAlignment) ? cls->requiredAlignment : 16;

#if !defined(__APPLE__) && (defined(__i686__) || (defined(__arm__) && !defined(__aarch64__)) || defined(_M_IX86) || defined(_M_ARM))
// Linux and Windows 32-bit targets perform 8-byte alignment by default.
static const kDefaultAlignment = 8;
#else
static const kDefaultAlignment = 16;
#endif

// Ensure that we get the alignment correct for various targets. In the
// case that we are over-aligned `swift_allocObject` will go through a
// different allocator to ensure that the pointer is suitably aligned. When
// we subsequently release the pointer we do not tag that release to go
// through the overalign'ed path. This may result in a cross-domainf free
// and a resultant heap corruption.
size_t align = (cls->version & _kCFRuntimeRequiresAlignment) ? cls->requiredAlignment : kDefaultAlignment;

CFRuntimeBase *memory = (CFRuntimeBase *)swift_allocObject(isa, size, align - 1);

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