cmd/tailcat: fix genkey --embed-derp-map panic without a fixed region - #91
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genkey --embed-derp-map looked up dm.Regions[ci.RegionID] and used the result without checking it. With --region left at its "auto" default, ci.RegionID is -1, meaning "probe for the nearest region at each server startup", so the lookup missed and the nil *tailcfg.DERPRegion crashed on the next line. Nothing can be embedded in that case: embedding bakes one region's nodes into the address, which is the opposite of choosing the region later. Reject an explicit --region=auto as contradictory, and treat the "auto" default as a request to pick the nearest region now, exactly as --fixed-region does, since --embed-derp-map already implies a fixed region. Two adjacent forms reached the same nil lookup. A --region naming DERP hostnames leaves RegionID 0 while already embedding those nodes, so it is now a usage error; a numeric region absent from the DERP map now names the missing region instead of panicking. Thanks to Ray Chan for the report! Fixes tailscale#90 Reported-by: Ray Chan (https://github.com/chanchiwai-ray) Signed-off-by: Ben B <gmkbenjamin@hotmail.com>
bradfitz
approved these changes
Sep 4, 2026
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Thanks. The tests are pretty heavy, but I can lighten those up later if they start to annoy me :) |
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genkey --embed-derp-map looked up dm.Regions[ci.RegionID] and used the
result without checking it. With --region left at its "auto" default,
ci.RegionID is -1, meaning "probe for the nearest region at each server
startup", so the lookup missed and the nil *tailcfg.DERPRegion crashed
on the next line.
Nothing can be embedded in that case: embedding bakes one region's
nodes into the address, which is the opposite of choosing the region
later. Reject an explicit --region=auto as contradictory, and treat the
"auto" default as a request to pick the nearest region now, exactly as
--fixed-region does, since --embed-derp-map already implies a fixed
region.
Two adjacent forms reached the same nil lookup. A --region naming DERP
hostnames leaves RegionID 0 while already embedding those nodes, so it
is now a usage error; a numeric region absent from the DERP map now
names the missing region instead of panicking.
Thanks to Ray Chan for the report!
Fixes #90