net/valkey: fix nil pointer panic in shardForKey - #4173
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shardForKey dereferences the atomic pointer without a nil check:
return *vr.shards[xxhash.Sum64String(key)%ringSize].Load()
When shard slots are not yet initialized (e.g. ring created with zero
addresses before AddrUpdater populates them), Load() returns nil and
the dereference panics. This crashes every request hitting a
Valkey-backed cluster rate limit filter:
panic caused by: runtime error: invalid memory address or nil pointer dereference
github.com/zalando/skipper/net.(*valkeyRing).shardForKey(0x363fc1b64000, {0x363fc15dcc00?, 0x0?})
github.com/zalando/skipper/net/valkey.go:249 +0x64
Change shardForKey to return (valkey.Client, error) and check for nil
before dereferencing. Propagate the error through all valkeyRing
methods and ValkeyRingClient wrappers so callers receive a proper error
instead of a panic.
An alternative approach would be to prevent nil from ever being stored
by ensuring newValkeyRing does not return a usable ring until
updateShards has run with at least one address, and guarding SetAddr
against partial initialization races. This would be a stronger
invariant but a larger change; the nil-check in shardForKey is the
minimal safety net that prevents the panic regardless of cause.
Signed-off-by: Thilina Madumal <thilina.madumal@zalando.de>
madumalt
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Logs of the Panic |
szuecs
reviewed
Aug 7, 2026
| // shardForKey does the lookup for valkey most operations to find the valkey ring shard | ||
| func (vr *valkeyRing) shardForKey(key string) valkey.Client { | ||
| return *vr.shards[xxhash.Sum64String(key)%ringSize].Load() | ||
| func (vr *valkeyRing) shardForKey(key string) (valkey.Client, error) { |
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we should not have a change here. We should fix the initial creation.
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Yeah that's what I proposed in the alternative approach. But atm I don't have all information how can I do it. Any leads?
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I think in skipper.go we create the valkey client. We could expose Ready() bool in valkey client and we do something like for !valkey.Ready() { time.Sleep(time.Second) } in skipper.go before we start the main listener that would make skipper "ready" for NLB and kubernetes.
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Ready() should check that the sharding client array has no nil entry or something like that.
madumalt
marked this pull request as draft
August 7, 2026 09:17
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shardForKey dereferences the atomic pointer without a nil check:
When shard slots are not yet initialized (e.g. ring created with zero addresses before AddrUpdater populates them), Load() returns nil and the dereference panics. This crashes every request hitting a Valkey-backed cluster rate limit filter:
Change shardForKey to return (valkey.Client, error) and check for nil before dereferencing. Propagate the error through all valkeyRing methods and ValkeyRingClient wrappers so callers receive a proper error instead of a panic.
Alternative Approach
An alternative approach would be to prevent nil from ever being stored by ensuring newValkeyRing does not return a usable ring until updateShards has run with at least one address, and guarding SetAddr against partial initialization races. This would be a stronger invariant but a larger change; the nil-check in shardForKey is the minimal safety net that prevents the panic regardless of cause.