dnsmasq: fix CVE-2026-2291

dnsmasqs extract_name() function can be abused to cause a heap buffer
overflow, allowing an attacker to inject false DNS cache entries, which
could result in DNS lookups to redirect to an attacker-controlled IP
address, or to cause a DoS.

This patch is used by debian bookworm (2.90-4_deb12u2).

Signed-off-by: Benjamin Robin (Schneider Electric) <benjamin.robin@bootlin.com>
Signed-off-by: Anuj Mittal <anuj.mittal@oss.qualcomm.com>

meta-networking/recipes-support/dnsmasq/dnsmasq_2.90.bb

@@ -20,6 +20,7 @@ SRC_URI = "http://www.thekelleys.org.uk/dnsmasq/${@['archive/', ''][float(d.getV
            file://CVE-2026-4892.patch \
            file://CVE-2026-4893.patch \
            file://CVE-2026-5172.patch \
+           file://CVE-2026-2291.patch \
 "
 SRC_URI[sha256sum] = "8f6666b542403b5ee7ccce66ea73a4a51cf19dd49392aaccd37231a2c51b303b"
 

meta-networking/recipes-support/dnsmasq/files/CVE-2026-2291.patch

@@ -0,0 +1,40 @@
+From c3059821cd52b423592aeffef7935fdf81035a81 Mon Sep 17 00:00:00 2001
+From: Simon Kelley <simon@thekelleys.org.uk>
+Date: Fri, 10 Apr 2026 16:29:31 +0100
+Subject: [PATCH] Fix buffer overflow in struct bigname. CVE-2026-2291
+
+All buffers capable of holding a domain name should be
+at least MAXDNAME*2 + 1 bytes long, where MAXDNAME is the maximum
+size of a domain name. The accounts for the trailing zero and the
+fact that some characters are escaped in the internal representation
+of a domain name in dnsmasq.
+
+The declaration of struct bigname get this wrong, with the effect
+that a remote attacker capable of asking DNS queries or answering DNS
+queries can cause a large OOB write in the heap.
+
+This was first spotted by Andrew S. Fasano.
+
+CVE: CVE-2026-2291
+Upstream-Status: Backport [https://sources.debian.org/src/dnsmasq/2.90-4~deb12u2/debian/patches/CVE-2026-2291.patch]
+
+Signed-off-by: Benjamin Robin <benjamin.robin@bootlin.com>
+---
+ src/dnsmasq.h | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/src/dnsmasq.h b/src/dnsmasq.h
+index e455c3f7..be8cf2ad 100644
+--- a/src/dnsmasq.h
++++ b/src/dnsmasq.h
+@@ -467,7 +467,7 @@ struct interface_name {
+ };
+
+ union bigname {
+-  char name[MAXDNAME];
++  char name[(2*MAXDNAME) + 1];
+   union bigname *next; /* freelist */
+ };
+
+--
+2.43.0