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Regression: Fix assigning to nil map in DeepMerge #18143

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merged 3 commits into from
May 4, 2020
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Regression: Fix assigning to nil map in DeepMerge #18143

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Regression: Fix assigning to nil map in DeepMerge
Apr 30, 2020
28966fe
Add changelog
Apr 30, 2020
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May 4, 2020
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1 change: 1 addition & 0 deletions CHANGELOG.next.asciidoc
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Original file line number Diff line number Diff line change
Expand Up @@ -80,6 +80,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
- Fix goroutine leak and Elasticsearch output file descriptor leak when output reloading is in use. {issue}10491[10491] {pull}17381[17381]
- Fix `setup.dashboards.index` setting not working. {pull}17749[17749]
- Fix Elasticsearch license endpoint URL referenced in error message. {issue}17880[17880] {pull}18030[18030]
- Fix panic when assigning a key to a `nil` value in an event. {pull}18143[18143]

*Auditbeat*

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16 changes: 11 additions & 5 deletions libbeat/common/mapstr.go
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Expand Up @@ -96,20 +96,26 @@ func (m MapStr) deepUpdateMap(d MapStr, overwrite bool) {
}

func deepUpdateValue(old interface{}, val MapStr, overwrite bool) interface{} {
if old == nil {
return val
}

switch sub := old.(type) {
case MapStr:
if sub == nil {
return val
}
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Surprised that this isn't caught already by the if old == nil check at the start of this function. 🤔

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Just found https://groups.google.com/forum/#!topic/golang-nuts/wnH302gBa4I/discussion.

Should we remove the code on lines 99-101?

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There is nil, and then there is nil :)

An interface value is a tuple (type, value). An interface is nil, if and only if both type and value are nil. This is why the initial check fails here. We have a type (type MapStr, nil). The switch statement only looks for type, unpacks it, and we finally have the nil value in sub. This is when the call panics.

Removing line 99 should be safe. E.g.: https://play.golang.org/p/uajkDxQW9qH


sub.deepUpdateMap(val, overwrite)
return sub
case map[string]interface{}:
if sub == nil {
return val
}

tmp := MapStr(sub)
tmp.deepUpdateMap(val, overwrite)
return tmp
default:
// This should never happen
// We reach the default branch if old is no map or if old == nil.
// In either case we return `val`, such that the old value is completely
// replaced when merging.
return val
}
}
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5 changes: 5 additions & 0 deletions libbeat/common/mapstr_test.go
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Expand Up @@ -87,6 +87,11 @@ func TestMapStrDeepUpdate(t *testing.T) {
MapStr{"a.b": 1},
MapStr{"a": 1, "a.b": 1},
},
{
MapStr{"a": (MapStr)(nil)},
MapStr{"a": MapStr{"b": 1}},
MapStr{"a": MapStr{"b": 1}},
},
}

for i, test := range tests {
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