libpng security vulnerability

[manoelneto]

@Chris Babcock;602013

4.13.1 was already completing testing when this came up.

If you have source from GitHub, you can use this ZIP update to get the new libpng version with prebuilt Android libraries: https://epicgames.app.box.com/s/abvk2gj65pg4ccdoin39sudi9y6uosvb

This should work with 4.12.x and 4.13.x as-is; let me know if there are any problems with older releases.

There are a few linking errors when building x86 and x86_64 APKs. To fix it, the Android.mk file in the zip needs to be modified like this:

Find this line:

LOCAL_CFLAGS := -O2 -Os -DNDEBUG -fomit-frame-pointer -g0

And add this right bellow it:

ifeq ($(TARGET_ARCH_ABI),x86)
	LOCAL_CFLAGS += -fno-stack-protector
endif
ifeq ($(TARGET_ARCH_ABI),x86_64)
	LOCAL_CFLAGS += -fno-stack-protector
endif

Then run “BuildForAndroid.bat” to re-compile the libPNG Android libraries.

The problem is caused UE4 uses the “stack-protector” compiler flag on arm7 and arm64 builds but not on x86/x86_64 ones, while libPNG was compiled with that flag for all architectures, causing linker conflicts.