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a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1729527614; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VVieedyPJlknzVmD9/TMYpfZlftz/s1bAD6yv7JeyO8=; b=G6jnqsnctE0CAfV7ljv17U3KwpEbUfGri6+NZ/DaWuF8k7VNe5/kEEajEY0QrFWpurtXB3 SCu0OhyIAct3OY7Y0scKCppcEMnFd82DBV3H/t5I4REQvyowkUM5Y369EadBBzkazuNX9D +CPStNvIX+eQU+dhIQ5mNg4L2PLV3WQ= X-MC-Unique: jzoSfU1pN1OPYINvDUK4TA-1 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= To: qemu-devel@nongnu.org Cc: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Subject: [PATCH 6/6] ui: validate NUL byte padding in SASL client data more strictly Date: Mon, 21 Oct 2024 17:19:57 +0100 Message-ID: <20241021161957.1431919-7-berrange@redhat.com> In-Reply-To: <20241021161957.1431919-1-berrange@redhat.com> References: <20241021161957.1431919-1-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.421, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1.699, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1729527655830116600 When the SASL data is non-NULL, the SASL protocol spec requires that it is padded with a trailing NUL byte. QEMU discards the trailing byte, but does not currently validate that it was in fact a NUL. Apply strict validation to better detect any broken clients. Signed-off-by: Daniel P. Berrang=C3=A9 --- ui/vnc-auth-sasl.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/ui/vnc-auth-sasl.c b/ui/vnc-auth-sasl.c index a04feeb429..df2825797d 100644 --- a/ui/vnc-auth-sasl.c +++ b/ui/vnc-auth-sasl.c @@ -263,8 +263,14 @@ static int protocol_client_auth_sasl_step(VncState *vs= , uint8_t *data, size_t le /* NB, distinction of NULL vs "" is *critical* in SASL */ if (datalen) { clientdata =3D (char*)data; - clientdata[datalen-1] =3D '\0'; /* Wire includes '\0', but make su= re */ - datalen--; /* Don't count NULL byte when passing to _start() */ + if (clientdata[datalen-1] !=3D '\0') { + trace_vnc_auth_fail(vs, vs->auth, "Malformed SASL client data", + "Missing SASL NUL padding byte"); + sasl_dispose(&vs->sasl.conn); + vs->sasl.conn =3D NULL; + goto authabort; + } + datalen--; /* Discard the extra NULL byte padding when calling _st= art() */ } =20 err =3D sasl_server_step(vs->sasl.conn, @@ -385,8 +391,14 @@ static int protocol_client_auth_sasl_start(VncState *v= s, uint8_t *data, size_t l /* NB, distinction of NULL vs "" is *critical* in SASL */ if (datalen) { clientdata =3D (char*)data; - clientdata[datalen-1] =3D '\0'; /* Should be on wire, but make sur= e */ - datalen--; /* Don't count NULL byte when passing to _start() */ + if (clientdata[datalen-1] !=3D '\0') { + trace_vnc_auth_fail(vs, vs->auth, "Malformed SASL client data= ", + "Missing SASL NUL padding byte"); + sasl_dispose(&vs->sasl.conn); + vs->sasl.conn =3D NULL; + goto authabort; + } + datalen--; /* Discard the extra NULL byte padding when calling _st= art() */ } =20 err =3D sasl_server_start(vs->sasl.conn, --=20 2.46.0