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You can check the libc version with:

dpkg -s libc6

For my Debian 7 servers it reports "Version: 2.13-38+deb7u7" after upgrading. Everything below that (eg. "*u6") is vulnerable. I don't know about the specific version numbers in Ubuntu though.

Edit: the fixed Ubuntu version is "2.15-0ubuntu10.10"

Per the Ubuntu security advisory for this, 14.04 is not impacted.

Full blog post coming, but 14.04 was never vulnerable. glibc 2.17 was the last vulnerable version.