The snd_msndmidi_input_read function in sound/isa/msnd/msnd_midi.c in the Linux kernel through 4.11.7 allows local users to cause a denial of service (over-boundary access) or possibly have unspecified other impact by changing the value of a message queue head pointer between two kernel reads of that value, aka a double fetch vulnerability. https://nvd.nist.gov/vuln/detail/CVE-2017-9985
