From fc233efad86101d49cd312b16c5a25e6a017e977 Mon Sep 17 00:00:00 2001 From: Thiago Macieira Date: Thu, 11 May 2023 21:40:15 -0700 Subject: [PATCH] QDnsLookup/Unix: make sure we don't overflow the buffer MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The DNS Records are variable length and encode their size in 16 bits before the Record Data (RDATA). Ensure that both the RDATA and the Record header fields before it fall inside the buffer we have. Additionally reject any replies containing more than one query records. [ChangeLog][QtNetwork][QDnsLookup] Fixed a bug that could cause a buffer overflow in Unix systems while parsing corrupt, malicious, or truncated replies. Pick-to: 5.15 6.2 6.5 6.5.1 Change-Id: I3e3bfef633af4130a03afffd175e4b9547654b95 Reviewed-by: Mårten Nordheim Reviewed-by: Jani Heikkinen Fixes: https://security-tracker.debian.org/tracker/CVE-2023-33285 Upstream: https://codereview.qt-project.org/gitweb?p=qt/qtbase.git;a=commitdiff;h=7dba2c87619d558a61a30eb30cc1d9c3fe6df94c [Thomas: changes needed to backport on 6.4.3: use local_dn_expand() instead of dn_expand(), since we didn't backport the changes in 68b625901f9eb7c34e3d7aa302e1c0a454d3190b that are too invasive] Signed-off-by: Thomas Petazzoni --- src/network/kernel/qdnslookup_unix.cpp | 31 +++++++++++++++++++++----- 1 file changed, 25 insertions(+), 6 deletions(-) diff --git a/src/network/kernel/qdnslookup_unix.cpp b/src/network/kernel/qdnslookup_unix.cpp index 75f7c6c440e..de0113494fc 100644 --- a/src/network/kernel/qdnslookup_unix.cpp +++ b/src/network/kernel/qdnslookup_unix.cpp @@ -193,7 +193,6 @@ void QDnsLookupRunnable::query(const int requestType, const QByteArray &requestN // responseLength in case of error, we still can extract the // exact error code from the response. HEADER *header = (HEADER*)response; - const int answerCount = ntohs(header->ancount); switch (header->rcode) { case NOERROR: break; @@ -226,18 +225,31 @@ void QDnsLookupRunnable::query(const int requestType, const QByteArray &requestN return; } - // Skip the query host, type (2 bytes) and class (2 bytes). char host[PACKETSZ], answer[PACKETSZ]; unsigned char *p = response + sizeof(HEADER); - int status = local_dn_expand(response, response + responseLength, p, host, sizeof(host)); - if (status < 0) { + int status; + + if (ntohs(header->qdcount) == 1) { + // Skip the query host, type (2 bytes) and class (2 bytes). + status = local_dn_expand(response, response + responseLength, p, host, sizeof(host)); + if (status < 0) { + reply->error = QDnsLookup::InvalidReplyError; + reply->errorString = tr("Could not expand domain name"); + return; + } + if ((p - response) + status + 4 >= responseLength) + header->qdcount = 0xffff; // invalid reply below + else + p += status + 4; + } + if (ntohs(header->qdcount) > 1) { reply->error = QDnsLookup::InvalidReplyError; - reply->errorString = tr("Could not expand domain name"); + reply->errorString = tr("Invalid reply received"); return; } - p += status + 4; // Extract results. + const int answerCount = ntohs(header->ancount); int answerIndex = 0; while ((p < response + responseLength) && (answerIndex < answerCount)) { status = local_dn_expand(response, response + responseLength, p, host, sizeof(host)); @@ -249,6 +261,11 @@ void QDnsLookupRunnable::query(const int requestType, const QByteArray &requestN const QString name = QUrl::fromAce(host); p += status; + + if ((p - response) + 10 > responseLength) { + // probably just a truncated reply, return what we have + return; + } const quint16 type = (p[0] << 8) | p[1]; p += 2; // RR type p += 2; // RR class @@ -256,6 +273,8 @@ void QDnsLookupRunnable::query(const int requestType, const QByteArray &requestN p += 4; const quint16 size = (p[0] << 8) | p[1]; p += 2; + if ((p - response) + size > responseLength) + return; // truncated if (type == QDnsLookup::A) { if (size != 4) { -- 2.46.0