The environment variable TMPDIR was copied unchecked into a fixed-size heap
buffer. Use a length-limiting snprintf in place of ordinary sprintf to
prevent the overflow. Long TMPDIR variables can still cause odd truncated
filenames, which may be undesirable.
Reported by: Coverity (CWE-120)
CIDs: 1006706, 1006707
Sponsored by: Dell EMC Isilon
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