So you've finally started to receive that official Samsung Android 4.4.2 KitKat update for your Galaxy S4 or Galaxy Note 3, or you might have just jumped the gun and decided you'd rather flash a custom ROM instead of endure the inevitable wait for your carrier. Thankfully the transition is super smooth, and your phone is going to feel faster and more efficient than ever thanks to Android 4.4 KitKat's improved memory management and behind-the-scenes enhancements. What isn't an enhancement though, and is something that seems to be unique to the Android 4.4.2 KitKat update for the Galaxy S4 and Note 3 only, is the near complete inability to use that precious SD card on your phone. Yes that's right, Samsung seems to have single-handedly messed up SD card support in KitKat, but it's not without an easy fix (if you're rooted that is). For those who aren't rooted it seems that your only options are to either not take the update until Samsung addresses the fix with a minor patch, or just to endure it until said patch comes along. We're not 100% sure which versions of the Note 3 or S4 this affects, as reports of non-working SD cards have been spotty at best, but it's safe to assume everyone who took the update will face this issue one way or another.
Basically the problem looks like this: if you're using an app that attempts to access the SD card to either modify, delete or create a new file, that app will be denied access to doing such a thing. The first time I ran into it was using a 3rd party camera app (i.e. not the built-in Samsung app), and noticed that none of the pictures I took were saving. I then tried to clear some space off my SD card using Solid Explorer (a root file browser) and wasn't able to change or delete anything at all on the SD card. Connecting it to my PC didn't exhibit this problem. It turns out that Samsung seems to have forgotten that Google changed the way SD cards worked in Android 4.4 KitKat, and presumably forgot to add the new permission to the permissions manifest file in the system. If you've got root access here's the quick and dirty fix:
First use your favorite root file browser to navigate to the file. Personally I like Solid Explorer, but many people also use ES File Explorer as well. Navigate to your root system directory, head on into the system folder, then etc, then permissions. Inside you'll find a "platform.xml" file, go ahead and open that with the file editor with the same name as your root browser (in my case SETextEditor since I'm using Solid Explorer). Scroll down about half way and you'll find a section with "WRITE_EXTERNAL_STORAGE" at the end of the name. Likely you'll already have the permissions "sdcard_r" and "sdcard_rw" underneath the header, but the 3rd permission is what allows us to actually do anything other than just read the SD card. Check the image below for the correct formatting, but make sure you add "" below the other two. If you're unsure of the formatting just copy one of the other ones and change sdcard to media.
Once that's all done go ahead and reboot your phone and give it a try. Just go into your file browser and try to create or delete any file on the SD card and see if you can. If it was successful than congrats, you've fixed the issue! This is such a small oversight that's going to create a major impact on a ton of users, especially since one of the biggest features of owning a Samsung phone is the ability to use an SD card in the first place, so we imagine Samsung will have an official fix soon if some of the new rollouts don't already include it. I'm not going to provide a flashable .zip file just in case your platform.xml is different from mine; you don't want to have to reflash your phone just for one silly little file after all. Feel free to leave any comments or ask questions if you're stuck or unsure of a certain part of the process!