glReadPixels returns incorrect image for iPhone 6, but works ok for iPad and iPhone 5

I'm using following code for reading on image from OpenGL ES scene:

- (UIImage *)drawableToCGImage
{
CGRect myRect = self.bounds;
NSInteger myDataLength = myRect.size.width * myRect.size.height * 4;

glFinish();
glPixelStorei(GL_PACK_ALIGNMENT, 4);

int width = myRect.size.width;
int height = myRect.size.height;

GLubyte *buffer = (GLubyte *) malloc(myDataLength);
GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer2);
for(int y1 = 0; y1 < height; y1++) {
    for(int x1 = 0; x1 < width * 4; x1++) {
        buffer[(height - 1 - y1) * width * 4 + x1] = buffer2[y1 * 4 * width + x1];
    }
}

free(buffer2);

CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, myDataLength, NULL);
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * myRect.size.width;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
CGImageRef imageRef = CGImageCreate(myRect.size.width, myRect.size.height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
UIImage *image = [UIImage imageWithCGImage:imageRef];

CGImageRelease(imageRef);

return image;
}

It works perfectly for iPad and old iPhone versions, but I noticed that on iPhone 6 (both device and simulators) it looks like monochrome glitches. What could it be?

Also, here is my code for CAEAGLLayer properties:

eaglLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                                @YES, kEAGLDrawablePropertyRetainedBacking,
                                kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];

Could somebody shed the light on this crazy magic, please?

Thanks to @MaticOblak, I've figured out the problem.

Buffer was filled incorrectly, because float values of rect size were not correctly rounded (yeah, only for iPhone 6 dimension). Instead integer values should be used.

UPD: my issue was fixed with the following code:

GLint viewport[4];
glGetIntegerv(GL_VIEWPORT, viewport);

int width = viewport[2];
int height = viewport[3];