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nftables: validate csumOffset bounds in payloadSet evaluate #13624

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nftables: validate csumOffset bounds in payloadSet evaluate #13624

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7 changes: 7 additions & 0 deletions pkg/tcpip/nftables/nft_payload_set.go
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Original file line number Diff line number Diff line change
Expand Up @@ -157,6 +157,13 @@ func (op payloadSet) evaluate(regs *registerSet, evalCtx opEvalCtx) {

// Updates the checksum of the header specified by the payload base.
if op.csumType == linux.NFT_PAYLOAD_CSUM_INET {
// Equivalent to Linux skb_copy_bits returning -1 when the
// checksum field is outside the packet; matches the data
// bounds check at line 105.
if int(op.csumOffset)+2 > len(payload) {
regs.verdict = stack.NFVerdict{Code: VC(linux.NFT_BREAK)}
return
}
// Reads the old checksum from the packet payload.
oldTotalCsum := binary.BigEndian.Uint16(payload[op.csumOffset:])

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14 changes: 14 additions & 0 deletions pkg/tcpip/nftables/nftables_test.go
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Expand Up @@ -2087,6 +2087,20 @@ func TestEvaluatePayloadSet(t *testing.T) {
op1: mustCreateImmediate(t, linux.NFT_REG_3, arbitraryIPv6AddrB[:], stack.NFVerdict{}),
op2: mustCreatePayloadSet(t, linux.NFT_PAYLOAD_NETWORK_HEADER, ipv6DstAddrOffset, ipv6DstAddrLen, linux.NFT_REG_3, linux.NFT_PAYLOAD_CSUM_NONE, 0, linux.NFT_PAYLOAD_L4CSUM_PSEUDOHDR),
},
{
tname: "csumOffset equal to network header length triggers NFT_BREAK",
pkt: makeIPv4Packet(header.IPv4MinimumSize, arbitraryIPv4Fields()),
outPkt: nil,
op1: mustCreateImmediate(t, linux.NFT_REG_1, numToBE(0, ipv4LengthLen), stack.NFVerdict{}),
op2: mustCreatePayloadSet(t, linux.NFT_PAYLOAD_NETWORK_HEADER, ipv4LengthOffset, ipv4LengthLen, linux.NFT_REG_1, linux.NFT_PAYLOAD_CSUM_INET, header.IPv4MinimumSize, 0x0),
},
{
tname: "csumOffset past network header length triggers NFT_BREAK",
pkt: makeIPv4Packet(header.IPv4MinimumSize, arbitraryIPv4Fields()),
outPkt: nil,
op1: mustCreateImmediate(t, linux.NFT_REG_1, numToBE(0, ipv4LengthLen), stack.NFVerdict{}),
op2: mustCreatePayloadSet(t, linux.NFT_PAYLOAD_NETWORK_HEADER, ipv4LengthOffset, ipv4LengthLen, linux.NFT_REG_1, linux.NFT_PAYLOAD_CSUM_INET, 250, 0x0),
},
} {
t.Run(test.tname, func(t *testing.T) {
// Sets up an NFTables object with a single table, chain, and rule.
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