From: Roy Marples <roy@marples.name>
Date: Mon, 8 May 2023 14:52:11 +0000 (+0100)
Subject: DHCP: Don't enforce the message came port 67
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6e127eac6903524d401b31893167e4529b8ab111;p=thirdparty%2Fdhcpcd.git

DHCP: Don't enforce the message came port 67

RFC2131 and updates make no mention of what the source port
should or must be.

Update for #179.
---

diff --git a/src/bpf.c b/src/bpf.c
index 339f3a01..44b08e6e 100644
--- a/src/bpf.c
+++ b/src/bpf.c
@@ -612,16 +612,19 @@ static const struct bpf_insn bpf_bootp_base[] = {
 #define BPF_BOOTP_BASE_LEN	__arraycount(bpf_bootp_base)
 
 static const struct bpf_insn bpf_bootp_read[] = {
-	/* Make sure it's from and to the right port. */
-	BPF_STMT(BPF_LD + BPF_W + BPF_IND, 0),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (BOOTPS << 16) + BOOTPC, 1, 0),
+	/* Make sure it's to the right port.
+	 * RFC2131 makes no mention of enforcing a source port. */
+	BPF_STMT(BPF_LD + BPF_H + BPF_IND, offsetof(struct udphdr, uh_dport)),
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, BOOTPC, 1, 0),
 	BPF_STMT(BPF_RET + BPF_K, 0),
 };
 #define BPF_BOOTP_READ_LEN	__arraycount(bpf_bootp_read)
 
 #ifdef BIOCSETWF
 static const struct bpf_insn bpf_bootp_write[] = {
-	/* Make sure it's from and to the right port. */
+	/* Make sure it's from and to the right port.
+	 * RFC2131 makes no mention of encforcing a source port,
+	 * but dhcpcd does enforce it for sending. */
 	BPF_STMT(BPF_LD + BPF_W + BPF_IND, 0),
 	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (BOOTPC << 16) + BOOTPS, 1, 0),
 	BPF_STMT(BPF_RET + BPF_K, 0),
diff --git a/src/dhcp.c b/src/dhcp.c
index f7680760..9a790b50 100644
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -3459,8 +3459,8 @@ is_packet_udp_bootp(void *packet, size_t plen)
 	if (ip_hlen + ntohs(udp.uh_ulen) > plen)
 		return false;
 
-	/* Check it's to and from the right ports. */
-	if (udp.uh_dport != htons(BOOTPC) || udp.uh_sport != htons(BOOTPS))
+	/* Check it's to the right port. */
+	if (udp.uh_dport != htons(BOOTPC))
 		return false;
 
 	return true;