From bf58c10dced30d34372fdfc4a778286370a4bfb8 Mon Sep 17 00:00:00 2001
From: Mark Andrews <marka@isc.org>
Date: Wed, 8 Mar 2023 16:05:03 +1100
Subject: [PATCH] Silence NULL pointer dereferene false positive

Only attempt to digest 'in' if it is non NULL.  This will prevent
false positives about NULL pointer dereferences against 'in' and
should also speed up the processing.
---
 lib/isc/siphash.c | 138 +++++++++++++++++++++++-----------------------
 1 file changed, 70 insertions(+), 68 deletions(-)

diff --git a/lib/isc/siphash.c b/lib/isc/siphash.c
index 46bd5de70a..ce24a6229f 100644
--- a/lib/isc/siphash.c
+++ b/lib/isc/siphash.c
@@ -90,51 +90,52 @@ isc_siphash24(const uint8_t *k, const uint8_t *in, const size_t inlen,
 
 	uint64_t b = ((uint64_t)inlen) << 56;
 
-	const uint8_t *end = (in == NULL)
-				     ? NULL
-				     : in + inlen - (inlen % sizeof(uint64_t));
-	const size_t left = inlen & 7;
+	if (in != NULL && inlen != 0) {
+		const uint8_t *end = in + inlen - (inlen % sizeof(uint64_t));
+		const size_t left = inlen & 7;
 
-	for (; in != end; in += 8) {
-		uint64_t m = case_sensitive
-				     ? ISC_U8TO64_LE(in)
-				     : isc_ascii_tolower8(ISC_U8TO64_LE(in));
+		for (; in != end; in += 8) {
+			uint64_t m =
+				case_sensitive
+					? ISC_U8TO64_LE(in)
+					: isc_ascii_tolower8(ISC_U8TO64_LE(in));
 
-		v3 ^= m;
+			v3 ^= m;
 
-		for (size_t i = 0; i < cROUNDS; ++i) {
-			SIPROUND(v0, v1, v2, v3);
+			for (size_t i = 0; i < cROUNDS; ++i) {
+				SIPROUND(v0, v1, v2, v3);
+			}
+
+			v0 ^= m;
 		}
 
-		v0 ^= m;
-	}
-
-	switch (left) {
-	case 7:
-		b |= U8TO64_ONE(case_sensitive, in[6]) << 48;
-		FALLTHROUGH;
-	case 6:
-		b |= U8TO64_ONE(case_sensitive, in[5]) << 40;
-		FALLTHROUGH;
-	case 5:
-		b |= U8TO64_ONE(case_sensitive, in[4]) << 32;
-		FALLTHROUGH;
-	case 4:
-		b |= U8TO64_ONE(case_sensitive, in[3]) << 24;
-		FALLTHROUGH;
-	case 3:
-		b |= U8TO64_ONE(case_sensitive, in[2]) << 16;
-		FALLTHROUGH;
-	case 2:
-		b |= U8TO64_ONE(case_sensitive, in[1]) << 8;
-		FALLTHROUGH;
-	case 1:
-		b |= U8TO64_ONE(case_sensitive, in[0]);
-		FALLTHROUGH;
-	case 0:
-		break;
-	default:
-		UNREACHABLE();
+		switch (left) {
+		case 7:
+			b |= U8TO64_ONE(case_sensitive, in[6]) << 48;
+			FALLTHROUGH;
+		case 6:
+			b |= U8TO64_ONE(case_sensitive, in[5]) << 40;
+			FALLTHROUGH;
+		case 5:
+			b |= U8TO64_ONE(case_sensitive, in[4]) << 32;
+			FALLTHROUGH;
+		case 4:
+			b |= U8TO64_ONE(case_sensitive, in[3]) << 24;
+			FALLTHROUGH;
+		case 3:
+			b |= U8TO64_ONE(case_sensitive, in[2]) << 16;
+			FALLTHROUGH;
+		case 2:
+			b |= U8TO64_ONE(case_sensitive, in[1]) << 8;
+			FALLTHROUGH;
+		case 1:
+			b |= U8TO64_ONE(case_sensitive, in[0]);
+			FALLTHROUGH;
+		case 0:
+			break;
+		default:
+			UNREACHABLE();
+		}
 	}
 
 	v3 ^= b;
@@ -173,39 +174,40 @@ isc_halfsiphash24(const uint8_t *k, const uint8_t *in, const size_t inlen,
 
 	uint32_t b = ((uint32_t)inlen) << 24;
 
-	const uint8_t *end = (in == NULL)
-				     ? NULL
-				     : in + inlen - (inlen % sizeof(uint32_t));
-	const int left = inlen & 3;
+	if (in != NULL && inlen != 0) {
+		const uint8_t *end = in + inlen - (inlen % sizeof(uint32_t));
+		const int left = inlen & 3;
 
-	for (; in != end; in += 4) {
-		uint32_t m = case_sensitive
-				     ? ISC_U8TO32_LE(in)
-				     : isc_ascii_tolower4(ISC_U8TO32_LE(in));
+		for (; in != end; in += 4) {
+			uint32_t m =
+				case_sensitive
+					? ISC_U8TO32_LE(in)
+					: isc_ascii_tolower4(ISC_U8TO32_LE(in));
 
-		v3 ^= m;
+			v3 ^= m;
 
-		for (size_t i = 0; i < cROUNDS; ++i) {
-			HALFSIPROUND(v0, v1, v2, v3);
+			for (size_t i = 0; i < cROUNDS; ++i) {
+				HALFSIPROUND(v0, v1, v2, v3);
+			}
+
+			v0 ^= m;
 		}
 
-		v0 ^= m;
-	}
-
-	switch (left) {
-	case 3:
-		b |= U8TO32_ONE(case_sensitive, in[2]) << 16;
-		FALLTHROUGH;
-	case 2:
-		b |= U8TO32_ONE(case_sensitive, in[1]) << 8;
-		FALLTHROUGH;
-	case 1:
-		b |= U8TO32_ONE(case_sensitive, in[0]);
-		FALLTHROUGH;
-	case 0:
-		break;
-	default:
-		UNREACHABLE();
+		switch (left) {
+		case 3:
+			b |= U8TO32_ONE(case_sensitive, in[2]) << 16;
+			FALLTHROUGH;
+		case 2:
+			b |= U8TO32_ONE(case_sensitive, in[1]) << 8;
+			FALLTHROUGH;
+		case 1:
+			b |= U8TO32_ONE(case_sensitive, in[0]);
+			FALLTHROUGH;
+		case 0:
+			break;
+		default:
+			UNREACHABLE();
+		}
 	}
 
 	v3 ^= b;