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crypto/tls: fix first byte test for 255 CBC padding bytes

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The BadCBCPadding255 test from bogo failed because at most 255 trailing
bytes were checked, but for a padding of 255 there are 255 padding bytes
plus 1 length byte with value 255.

Change-Id: I7dd237c013d2c7c8599067246e31b7ba93106cf7
Reviewed-on: https://go-review.googlesource.com/68070
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Peter Wu 2017-10-04 13:44:34 +01:00 committed by Adam Langley
parent 51cfe6849a
commit cb3b345209
2 changed files with 16 additions and 3 deletions
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7
src/crypto/tls/conn.go
View File

@ -213,10 +213,11 @@ func extractPadding(payload []byte) (toRemove int, good byte) {
// if len(payload) >= (paddingLen - 1) then the MSB of t is zero
good = byte(int32(^t) >> 31)
toCheck := 255 // the maximum possible padding length
// The maximum possible padding length plus the actual length field
toCheck := 256
// The length of the padded data is public, so we can use an if here
if toCheck+1 > len(payload) {
toCheck = len(payload) - 1
if toCheck > len(payload) {
toCheck = len(payload)
}
for i := 0; i < toCheck; i++ {

12
src/crypto/tls/conn_test.go
View File

@ -21,6 +21,12 @@ func TestRoundUp(t *testing.T) {
}
}
// will be initialized with {0, 255, 255, ..., 255}
var padding255Bad = [256]byte{}
// will be initialized with {255, 255, 255, ..., 255}
var padding255Good = [256]byte{255}
var paddingTests = []struct {
in []byte
good bool
@ -36,9 +42,15 @@ var paddingTests = []struct {
{[]byte{1, 4, 4, 4, 4, 4}, true, 1},
{[]byte{5, 5, 5, 5, 5, 5}, true, 0},
{[]byte{6, 6, 6, 6, 6, 6}, false, 0},
{padding255Bad[:], false, 0},
{padding255Good[:], true, 0},
}
func TestRemovePadding(t *testing.T) {
for i := 1; i < len(padding255Bad); i++ {
padding255Bad[i] = 255
padding255Good[i] = 255
}
for i, test := range paddingTests {
paddingLen, good := extractPadding(test.in)
expectedGood := byte(255)