Copy input data if slice has additional space

The additional space could be corrupted, because some libraries check
for slice capacity and use the available additional space of the slice.

core.go

@@ -19,6 +19,15 @@ func (s *Session) Close(data []byte) (*Letter, error) { //nolint:gocognit
 		letter.SuiteID = s.envelope.SuiteID
 	}
 
+	// Check for additional data in slice, which we should not touch.
+	// TODO: Pre-allocate needed overhead for AEAD and others.
+	if len(data) != cap(data) {
+		// Make a copy of the data in order to not modify unrelated data.
+		copiedData := make([]byte, len(data))
+		copy(copiedData, data)
+		data = copiedData
+	}
+
 	/////////////////
 	// key management
 	/////////////////

go.sum

@@ -23,6 +23,7 @@ github.com/StackExchange/wmi v0.0.0-20210224194228-fe8f1750fd46/go.mod h1:3eOhrU
 github.com/VictoriaMetrics/metrics v1.15.2/go.mod h1:Z1tSfPfngDn12bTfZSCqArT3OPY3u88J12hSoOhuiRE=
 github.com/aead/ecdh v0.2.0 h1:pYop54xVaq/CEREFEcukHRZfTdjiWvYIsZDXXrBapQQ=
 github.com/aead/ecdh v0.2.0/go.mod h1:a9HHtXuSo8J1Js1MwLQx2mBhkXMT6YwUmVVEY4tTB8U=
+github.com/aead/serpent v0.0.0-20160714141033-fba169763ea6 h1:5L8Mj9Co9sJVgW3TpYk2gxGJnDjsYuboNTcRmbtGKGs=
 github.com/aead/serpent v0.0.0-20160714141033-fba169763ea6/go.mod h1:3HgLJ9d18kXMLQlJvIY3+FszZYMxCz8WfE2MQ7hDY0w=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
@@ -35,6 +36,7 @@ github.com/beorn7/perks v0.0.0-20180321164747-3a771d992973/go.mod h1:Dwedo/Wpr24
 github.com/beorn7/perks v1.0.0/go.mod h1:KWe93zE9D1o94FZ5RNwFwVgaQK1VOXiVxmqh+CedLV8=
 github.com/bgentry/speakeasy v0.1.0/go.mod h1:+zsyZBPWlz7T6j88CTgSN5bM796AkVf0kBD4zp0CCIs=
 github.com/bketelsen/crypt v0.0.3-0.20200106085610-5cbc8cc4026c/go.mod h1:MKsuJmJgSg28kpZDP6UIiPt0e0Oz0kqKNGyRaWEPv84=
+github.com/bluele/gcache v0.0.2 h1:WcbfdXICg7G/DGBh1PFfcirkWOQV+v077yF1pSy3DGw=
 github.com/bluele/gcache v0.0.2/go.mod h1:m15KV+ECjptwSPxKhOhQoAFQVtUFjTVkc3H8o0t/fp0=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/cespare/xxhash v1.1.0/go.mod h1:XrSqR1VqqWfGrhpAt58auRo0WTKS1nRRg3ghfAqPWnc=
@@ -70,6 +72,7 @@ github.com/go-logfmt/logfmt v0.3.0/go.mod h1:Qt1PoO58o5twSAckw1HlFXLmHsOX5/0LbT9
 github.com/go-logfmt/logfmt v0.4.0/go.mod h1:3RMwSq7FuexP4Kalkev3ejPJsZTpXXBr9+V4qmtdjCk=
 github.com/go-ole/go-ole v1.2.5/go.mod h1:pprOEPIfldk/42T2oK7lQ4v4JSDwmV0As9GaiUsvbm0=
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
+github.com/gofrs/uuid v4.0.0+incompatible h1:1SD/1F5pU8p29ybwgQSwpQk+mwdRrXCYuPhW6m+TnJw=
 github.com/gofrs/uuid v4.0.0+incompatible/go.mod h1:b2aQJv3Z4Fp6yNu3cdSllBxTCLRxnplIgP/c0N/04lM=
 github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
 github.com/gogo/protobuf v1.2.1/go.mod h1:hp+jE20tsWTFYpLwKvXlhS1hjn+gTNwPg2I6zVXpSg4=
@@ -103,7 +106,9 @@ github.com/google/renameio v0.1.0/go.mod h1:KWCgfxg9yswjAJkECMjeO8J8rahYeXnNhOm4
 github.com/googleapis/gax-go/v2 v2.0.4/go.mod h1:0Wqv26UfaUD9n4G6kQubkQ+KchISgw+vpHVxEJEs9eg=
 github.com/googleapis/gax-go/v2 v2.0.5/go.mod h1:DWXyrwAJ9X0FpwwEdw+IPEYBICEFu5mhpdKc/us6bOk=
 github.com/gopherjs/gopherjs v0.0.0-20181017120253-0766667cb4d1/go.mod h1:wJfORRmW1u3UXTncJ5qlYoELFm8eSnnEO6hX4iZ3EWY=
+github.com/gorilla/mux v1.8.0 h1:i40aqfkR1h2SlN9hojwV5ZA91wcXFOvkdNIeFDP5koI=
 github.com/gorilla/mux v1.8.0/go.mod h1:DVbg23sWSpFRCP0SfiEN6jmj59UnW/n46BH5rLB71So=
+github.com/gorilla/websocket v1.4.2 h1:+/TMaTYc4QFitKJxsQ7Yye35DkWvkdLcvGKqM+x0Ufc=
 github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/grpc-ecosystem/go-grpc-middleware v1.0.0/go.mod h1:FiyG127CGDf3tlThmgyCl78X/SZQqEOJBCDaAfeWzPs=
 github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0/go.mod h1:8NvIoxWQoOIhqOTXgfV/d3M/q6VIi02HzZEHgUlZvzk=
@@ -209,8 +214,11 @@ github.com/safing/portbase v0.11.0/go.mod h1:Xb0htNFFEb6BlkloWyVbQoUguUMGrTVmEDw
 github.com/satori/go.uuid v1.2.0 h1:0uYX9dsZ2yD7q2RtLRtPSdGDWzjeM3TbMJP9utgA0ww=
 github.com/satori/go.uuid v1.2.0/go.mod h1:dA0hQrYB0VpLJoorglMZABFdXlWrHn1NEOzdhQKdks0=
 github.com/sean-/seed v0.0.0-20170313163322-e2103e2c3529/go.mod h1:DxrIzT+xaE7yg65j358z/aeFdxmN0P9QXhEzd20vsDc=
+github.com/seehuhn/fortuna v1.0.1 h1:lu9+CHsmR0bZnx5Ay646XvCSRJ8PJTi5UYJwDBX68H0=
 github.com/seehuhn/fortuna v1.0.1/go.mod h1:LX8ubejCnUoT/hX+1aKUtbKls2H6DRkqzkc7TdR3iis=
+github.com/seehuhn/sha256d v1.0.0 h1:TXTsAuEWr02QjRm153Fnvvb6fXXDo7Bmy1FizxarGYw=
 github.com/seehuhn/sha256d v1.0.0/go.mod h1:PEuxg9faClSveVuFXacQmi+NtDI/PX8bpKjtNzf2+s4=
+github.com/shirou/gopsutil v3.21.2+incompatible h1:U+YvJfjCh6MslYlIAXvPtzhW3YZEtc9uncueUNpD/0A=
 github.com/shirou/gopsutil v3.21.2+incompatible/go.mod h1:5b4v6he4MtMOwMlS0TUMTu2PcXUg8+E1lC7eC3UO/RA=
 github.com/shurcooL/sanitized_anchor_name v1.0.0/go.mod h1:1NzhyTcUVG4SuEtjjoZeVRXNmyL/1OwPU0+IJeTBvfc=
 github.com/sirupsen/logrus v1.2.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=
@@ -244,10 +252,14 @@ github.com/tevino/abool v0.0.0-20170917061928-9b9efcf221b5 h1:hNna6Fi0eP1f2sMBe/
 github.com/tevino/abool v0.0.0-20170917061928-9b9efcf221b5/go.mod h1:f1SCnEOt6sc3fOJfPQDRDzHOtSXuTtnz0ImG9kPRDV0=
 github.com/tevino/abool v1.2.0 h1:heAkClL8H6w+mK5md9dzsuohKeXHUpY7Vw0ZCKW+huA=
 github.com/tevino/abool v1.2.0/go.mod h1:qc66Pna1RiIsPa7O4Egxxs9OqkuxDX55zznh9K07Tzg=
+github.com/tidwall/gjson v1.6.8 h1:CTmXMClGYPAmln7652e69B7OLXfTi5ABcPPwjIWUv7w=
 github.com/tidwall/gjson v1.6.8/go.mod h1:zeFuBCIqD4sN/gmqBzZ4j7Jd6UcA2Fc56x7QFsv+8fI=
+github.com/tidwall/match v1.0.3 h1:FQUVvBImDutD8wJLN6c5eMzWtjgONK9MwIBCOrUJKeE=
 github.com/tidwall/match v1.0.3/go.mod h1:eRSPERbgtNPcGhD8UCthc6PmLEQXEWd3PRB5JTxsfmM=
 github.com/tidwall/pretty v1.0.2/go.mod h1:XNkn88O1ChpSDQmQeStsy+sBenx6DDtFZJxhVysOjyk=
+github.com/tidwall/pretty v1.1.0 h1:K3hMW5epkdAVwibsQEfR/7Zj0Qgt4DxtNumTq/VloO8=
 github.com/tidwall/pretty v1.1.0/go.mod h1:XNkn88O1ChpSDQmQeStsy+sBenx6DDtFZJxhVysOjyk=
+github.com/tidwall/sjson v1.1.5 h1:wsUceI/XDyZk3J1FUvuuYlK62zJv2HO2Pzb8A5EWdUE=
 github.com/tidwall/sjson v1.1.5/go.mod h1:VuJzsZnTowhSxWdOgsAnb886i4AjEyTkk7tNtsL7EYE=
 github.com/tklauser/go-sysconf v0.3.4/go.mod h1:Cl2c8ZRWfHD5IrfHo9VN+FX9kCFjIOyVklgXycLB6ek=
 github.com/tklauser/numcpus v0.2.1/go.mod h1:9aU+wOc6WjUIZEwWMP62PL/41d65P+iks1gBkr4QyP8=