btrfs: fix extent map use-after-free when handling missing device in read_one_chunk

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix extent map use-after-free when handling missing device in read_one_chunk Store the error code before freeing the extent_map. Though it's reference counted structure, in that function it's the first and last allocation so this would lead to a potential use-after-free. The error can happen eg. when chunk is stored on a missing device and the degraded mount option is missing. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216721

References

• https://git.kernel.org/stable/c/b8e7ed42bc3ca0d0e4191ee394d34962d3624c22
• https://git.kernel.org/stable/c/fce3713197ebba239e1c7e02174ed216ea1ee014
• https://git.kernel.org/stable/c/169a4cf46882974d4db6d85eb623ec898e51bbc0
• https://git.kernel.org/stable/c/1742e1c90c3da344f3bb9b1f1309b3f47482756a