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Thu, 15 Jan 2026 14:09:50 -0800 (PST) X-Received: by 2002:a05:620a:4443:b0:8c6:a8be:ecb1 with SMTP id af79cd13be357-8c6a8beed71mr6306785a.81.1768514989697; Thu, 15 Jan 2026 14:09:49 -0800 (PST) Received: from fedora ([198.48.244.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8c6a71c1a15sm60670385a.20.2026.01.15.14.09.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Jan 2026 14:09:49 -0800 (PST) From: Carlos O'Donell To: libc-alpha@sourceware.org, fweimer@redhat.com Cc: Carlos O'Donell Subject: [PATCH] resolv: Fix NSS DNS backend for gethostbyaddr (CVE-2026-0915) Date: Thu, 15 Jan 2026 17:09:36 -0500 Message-ID: <20260115220945.1904095-1-carlos@redhat.com> X-Mailer: git-send-email 2.52.0 MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: vNoIw3Uef8Pdcu0Pvf-AO6T8CrAb0sS-cxOE7knZycM_1768514991 X-Mimecast-Originator: redhat.com Content-type: text/plain; charset=UTF-8 X-Spam-Status: No, score=-11.9 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_BLOCKED, RCVD_IN_MSPIKE_H2, RCVD_IN_VALIDITY_RPBL_BLOCKED, RCVD_IN_VALIDITY_SAFE_BLOCKED, SPF_HELO_PASS, SPF_NONE, TXREP, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces~patchwork=sourceware.org@sourceware.org The default network value of zero for net was never tested for and results in a DNS query constructed from uninitialized stack bytes. The solution is to provide a default query for the case where net is zero. Adding a test case for this was straight forward given the existence of tst-resolv-network and if the test is added without the fix you observe this failure: FAIL: resolv/tst-resolv-network original exit status 1 error: tst-resolv-network.c:174: invalid QNAME: \146\218\129\128 error: 1 test failures With a random QNAME resulting from the use of uninitialized stack bytes. After the fix the test passes. Additionally verified using wireshark before and after to ensure on-the-wire bytes for the DNS query were as expected. No regressions on x86_64. --- resolv/nss_dns/dns-network.c | 4 ++++ resolv/tst-resolv-network.c | 6 ++++++ 2 files changed, 10 insertions(+) diff --git a/resolv/nss_dns/dns-network.c b/resolv/nss_dns/dns-network.c index e7d8866867..b7049b97b6 100644 --- a/resolv/nss_dns/dns-network.c +++ b/resolv/nss_dns/dns-network.c @@ -207,6 +207,10 @@ _nss_dns_getnetbyaddr_r (uint32_t net, int type, struct netent *result, sprintf (qbuf, "%u.%u.%u.%u.in-addr.arpa", net_bytes[3], net_bytes[2], net_bytes[1], net_bytes[0]); break; + default: + /* Default network (net is originally zero). */ + sprintf (qbuf, "0.0.0.0.in-addr.arpa"); + break; } net_buffer.buf = orig_net_buffer = (querybuf *) alloca (1024); diff --git a/resolv/tst-resolv-network.c b/resolv/tst-resolv-network.c index e62f4ee0e7..f6424939e4 100644 --- a/resolv/tst-resolv-network.c +++ b/resolv/tst-resolv-network.c @@ -46,6 +46,9 @@ handle_code (const struct resolv_response_context *ctx, { switch (code) { + case 0: + send_ptr (b, qname, qclass, qtype, "0.in-addr.arpa"); + break; case 1: send_ptr (b, qname, qclass, qtype, "1.in-addr.arpa"); break; @@ -265,6 +268,9 @@ do_test (void) "error: TRY_AGAIN\n"); /* Lookup by address, success cases. */ + check_reverse (0, + "name: 0.in-addr.arpa\n" + "net: 0x00000000\n"); check_reverse (1, "name: 1.in-addr.arpa\n" "net: 0x00000001\n");