Description: btrfs: crafted image triggers WARN() in __btrfs_free_extent
References:
 https://github.com/bobfuzzer/CVE/tree/master/CVE-2019-19039
Notes:
 bwh> The reporter describes this as an information leak because a WARN()
 bwh> causes register contents to be logged.  This is mitigated on stretch
 bwh> onward because we restrict access to the kernel log by default.
 bwh> However this can still be a denial-of-service if panic_on_warn is
 bwh> enabled.
Bugs:
upstream: needed
4.19-upstream-stable:
4.9-upstream-stable:
3.16-upstream-stable: ignored "EOL"
sid: needed
4.19-buster-security:
4.9-stretch-security:
3.16-jessie-security: ignored "EOL"