From 32b21da4bae5b8fbe0f42c31b723c4963b4b2512 Mon Sep 17 00:00:00 2001

From: Demi Marie Obenour <demi@invisiblethingslab.com>

Date: Thu, 6 May 2021 18:34:45 -0400

Subject: [PATCH] Validate and require subkey binding signatures on PGP public

 keys

All subkeys must be followed by a binding signature by the primary key

as per the OpenPGP RFC, enforce the presence and validity in the parser.

The implementation is as kludgey as they come to work around our

simple-minded parser structure without touching API, to maximise

backportability. Store all the raw packets internally as we decode them

to be able to access previous elements at will, needed to validate ordering

and access the actual data. Add testcases for manipulated keys whose

import previously would succeed.

Combined with:

5ff86764b17f31535cb247543a90dd739076ec38

b5e8bc74b2b05aa557f663fe227b94d2bc64fbd8

9f03f42e2614a68f589f9db8fe76287146522c0c

b6dffb6dc5ffa2ddc389743f0507876cab341315 (mem-leak fix)

ae3d2d234ae47ff85229d3fce97a266fa1aa5a61 (use-after-free fix)

Fixes CVE-2021-3521.

---

 rpmio/rpmpgp.c                                | 122 +++++++++++++++---

 sign/rpmgensig.c                              |   2 +-

 tests/Makefile.am                             |   3 +

 tests/data/keys/CVE-2021-3521-badbind.asc     |  25 ++++

 .../data/keys/CVE-2021-3521-nosubsig-last.asc |  25 ++++

 tests/data/keys/CVE-2021-3521-nosubsig.asc    |  37 ++++++

 tests/rpmsigdig.at                            |  28 ++++

 7 files changed, 224 insertions(+), 18 deletions(-)

 create mode 100644 tests/data/keys/CVE-2021-3521-badbind.asc

 create mode 100644 tests/data/keys/CVE-2021-3521-nosubsig-last.asc

 create mode 100644 tests/data/keys/CVE-2021-3521-nosubsig.asc

diff --git a/rpmio/rpmpgp.c b/rpmio/rpmpgp.c

index d0688ebe9..3372d577d 100644

--- a/rpmio/rpmpgp.c

+++ b/rpmio/rpmpgp.c

@@ -515,7 +515,7 @@ pgpDigAlg pgpDigAlgFree(pgpDigAlg alg)

     return NULL;

 }

-static int pgpPrtSigParams(pgpTag tag, uint8_t pubkey_algo, uint8_t sigtype,

+static int pgpPrtSigParams(pgpTag tag, uint8_t pubkey_algo,

 		const uint8_t *p, const uint8_t *h, size_t hlen,

 		pgpDigParams sigp)

 {

@@ -528,10 +528,8 @@ static int pgpPrtSigParams(pgpTag tag, uint8_t pubkey_algo, uint8_t sigtype,

 	int mpil = pgpMpiLen(p);

 	if (p + mpil > pend)

 	    break;

-	if (sigtype == PGPSIGTYPE_BINARY || sigtype == PGPSIGTYPE_TEXT) {

-	    if (sigalg->setmpi(sigalg, i, p))

-		break;

-	}

+	if (sigalg->setmpi(sigalg, i, p))

+	    break;

 	p += mpil;

     }

@@ -604,7 +602,7 @@ static int pgpPrtSig(pgpTag tag, const uint8_t *h, size_t hlen,

 	}

 	p = ((uint8_t *)v) + sizeof(*v);

-	rc = pgpPrtSigParams(tag, v->pubkey_algo, v->sigtype, p, h, hlen, _digp);

+	rc = pgpPrtSigParams(tag, v->pubkey_algo, p, h, hlen, _digp);

     }	break;

     case 4:

     {   pgpPktSigV4 v = (pgpPktSigV4)h;

@@ -662,7 +660,7 @@ static int pgpPrtSig(pgpTag tag, const uint8_t *h, size_t hlen,

 	if (p > (h + hlen))

 	    return 1;

-	rc = pgpPrtSigParams(tag, v->pubkey_algo, v->sigtype, p, h, hlen, _digp);

+	rc = pgpPrtSigParams(tag, v->pubkey_algo, p, h, hlen, _digp);

     }	break;

     default:

 	rpmlog(RPMLOG_WARNING, _("Unsupported version of key: V%d\n"), version);

@@ -1041,36 +1039,127 @@ unsigned int pgpDigParamsAlgo(pgpDigParams digp, unsigned int algotype)

     return algo;

 }

+static pgpDigParams pgpDigParamsNew(uint8_t tag)

+{

+    pgpDigParams digp = xcalloc(1, sizeof(*digp));

+    digp->tag = tag;

+    return digp;

+}

+

+static int hashKey(DIGEST_CTX hash, const struct pgpPkt *pkt, int exptag)

+{

+    int rc = -1;

+    if (pkt->tag == exptag) {

+	uint8_t head[] = {

+	    0x99,

+	    (pkt->blen >> 8),

+	    (pkt->blen     ),

+	};

+

+	rpmDigestUpdate(hash, head, 3);

+	rpmDigestUpdate(hash, pkt->body, pkt->blen);

+	rc = 0;

+    }

+    return rc;

+}

+

+static int pgpVerifySelf(pgpDigParams key, pgpDigParams selfsig,

+			const struct pgpPkt *all, int i)

+{

+    int rc = -1;

+    DIGEST_CTX hash = NULL;

+

+    switch (selfsig->sigtype) {

+    case PGPSIGTYPE_SUBKEY_BINDING:

+	hash = rpmDigestInit(selfsig->hash_algo, 0);

+	if (hash) {

+	    rc = hashKey(hash, &all[0], PGPTAG_PUBLIC_KEY);

+	    if (!rc)

+		rc = hashKey(hash, &all[i-1], PGPTAG_PUBLIC_SUBKEY);

+	}

+	break;

+    default:

+	/* ignore types we can't handle */

+	rc = 0;

+	break;

+    }

+

+    if (hash && rc == 0)

+	rc = pgpVerifySignature(key, selfsig, hash);

+

+    rpmDigestFinal(hash, NULL, NULL, 0);

+

+    return rc;

+}

+

 int pgpPrtParams(const uint8_t * pkts, size_t pktlen, unsigned int pkttype,

 		 pgpDigParams * ret)

 {

     const uint8_t *p = pkts;

     const uint8_t *pend = pkts + pktlen;

     pgpDigParams digp = NULL;

-    struct pgpPkt pkt;

+    pgpDigParams selfsig = NULL;

+    int i = 0;

+    int alloced = 16; /* plenty for normal cases */

+    struct pgpPkt *all = xmalloc(alloced * sizeof(*all));

     int rc = -1; /* assume failure */

+    int expect = 0;

+    int prevtag = 0;

     while (p < pend) {

-	if (decodePkt(p, (pend - p), &pkt))

+	struct pgpPkt *pkt = &all[i];

+	if (decodePkt(p, (pend - p), pkt))

 	    break;

 	if (digp == NULL) {

-	    if (pkttype && pkt.tag != pkttype) {

+	    if (pkttype && pkt->tag != pkttype) {

 		break;

 	    } else {

-		digp = xcalloc(1, sizeof(*digp));

-		digp->tag = pkt.tag;

+		digp = pgpDigParamsNew(pkt->tag);

 	    }

 	}

-	if (pgpPrtPkt(&pkt, digp))

+	if (expect) {

+	    if (pkt->tag != expect)

+		break;

+	    selfsig = pgpDigParamsNew(pkt->tag);

+	}

+

+	if (pgpPrtPkt(pkt, selfsig ? selfsig : digp))

 	    break;

-	p += (pkt.body - pkt.head) + pkt.blen;

+	if (selfsig) {

+	    /* subkeys must be followed by binding signature */

+	    int xx = 1; /* assume failure */

+

+	    if (!(prevtag == PGPTAG_PUBLIC_SUBKEY &&

+		  selfsig->sigtype != PGPSIGTYPE_SUBKEY_BINDING))

+		xx = pgpVerifySelf(digp, selfsig, all, i);

+

+	    selfsig = pgpDigParamsFree(selfsig);

+	    if (xx)

+		break;

+	    expect = 0;

+	}

+

+	if (pkt->tag == PGPTAG_PUBLIC_SUBKEY)

+	    expect = PGPTAG_SIGNATURE;

+	prevtag = pkt->tag;

+

+	i++;

+	p += (pkt->body - pkt->head) + pkt->blen;

+	if (pkttype == PGPTAG_SIGNATURE)

+	    break;

+

+	if (alloced <= i) {

+	    alloced *= 2;

+	    all = xrealloc(all, alloced * sizeof(*all));

+	}

     }

-    rc = (digp && (p == pend)) ? 0 : -1;

+    rc = (digp && (p == pend) && expect == 0) ? 0 : -1;

+    free(all);

     if (ret && rc == 0) {

 	*ret = digp;

     } else {

@@ -1105,8 +1194,7 @@ int pgpPrtParamsSubkeys(const uint8_t *pkts, size_t pktlen,

 		digps = xrealloc(digps, alloced * sizeof(*digps));

 	    }

-	    digps[count] = xcalloc(1, sizeof(**digps));

-	    digps[count]->tag = PGPTAG_PUBLIC_SUBKEY;

+	    digps[count] = pgpDigParamsNew(PGPTAG_PUBLIC_SUBKEY);

 	    /* Copy UID from main key to subkey */

 	    digps[count]->userid = xstrdup(mainkey->userid);

diff --git a/sign/rpmgensig.c b/sign/rpmgensig.c

index e5d191cc0..988a0f611 100644

--- a/sign/rpmgensig.c

+++ b/sign/rpmgensig.c

@@ -351,7 +351,7 @@ static int haveSignature(rpmtd sigtd, Header h)

 	pgpPrtParams(oldtd.data, oldtd.count, PGPTAG_SIGNATURE, &sig2;;

 	if (pgpDigParamsCmp(sig1, sig2) == 0)

 	    rc = 1;

-	pgpDigParamsFree(sig2);

+	sig2 = pgpDigParamsFree(sig2);

     }

     pgpDigParamsFree(sig1);

     rpmtdFreeData(&oldtd);

diff --git a/tests/Makefile.am b/tests/Makefile.am

index f742a9e1d..328234278 100644

--- a/tests/Makefile.am

+++ b/tests/Makefile.am

@@ -107,6 +107,9 @@ EXTRA_DIST += data/SPECS/hello-config-buildid.spec

 EXTRA_DIST += data/SPECS/hello-cd.spec

 EXTRA_DIST += data/keys/rpm.org-rsa-2048-test.pub

 EXTRA_DIST += data/keys/rpm.org-rsa-2048-test.secret

+EXTRA_DIST += data/keys/CVE-2021-3521-badbind.asc

+EXTRA_DIST += data/keys/CVE-2021-3521-nosubsig.asc

+EXTRA_DIST += data/keys/CVE-2021-3521-nosubsig-last.asc

 EXTRA_DIST += data/macros.testfile

 EXTRA_DIST += data/macros.debug

 EXTRA_DIST += data/SOURCES/foo.c

diff --git a/tests/data/keys/CVE-2021-3521-badbind.asc b/tests/data/keys/CVE-2021-3521-badbind.asc

new file mode 100644

index 000000000..aea00f9d7

--- /dev/null

+++ b/tests/data/keys/CVE-2021-3521-badbind.asc

@@ -0,0 +1,25 @@

+-----BEGIN PGP PUBLIC KEY BLOCK-----

+Version: rpm-4.17.90 (NSS-3)

+

+mQENBFjmORgBCAC7TMEk6wnjSs8Dr4yqSScWdU2pjcqrkTxuzdWvowcIUPZI0w/g

+HkRqGd4apjvY2V15kjL10gk3QhFP3pZ/9p7zh8o8NHX7aGdSGDK7NOq1eFaErPRY

+91LW9RiZ0lbOjXEzIL0KHxUiTQEmdXJT43DJMFPyW9fkCWg0OltiX618FUdWWfI8

+eySdLur1utnqBvdEbCUvWK2RX3vQZQdvEBODnNk2pxqTyV0w6VPQ96W++lF/5Aas

+7rUv3HIyIXxIggc8FRrnH+y9XvvHDonhTIlGnYZN4ubm9i4y3gOkrZlGTrEw7elQ

+1QeMyG2QQEbze8YjpTm4iLABCBrRfPRaQpwrABEBAAG0IXJwbS5vcmcgUlNBIHRl

+c3RrZXkgPHJzYUBycG0ub3JnPokBNwQTAQgAIQUCWOY5GAIbAwULCQgHAgYVCAkK

+CwIEFgIDAQIeAQIXgAAKCRBDRFkeGWTF/MxxCACnjqFL+MmPh9W9JQKT2DcLbBzf

+Cqo6wcEBoCOcwgRSk8dSikhARoteoa55JRJhuMyeKhhEAogE9HRmCPFdjezFTwgB

+BDVBpO2dZ023mLXDVCYX3S8pShOgCP6Tn4wqCnYeAdLcGg106N4xcmgtcssJE+Pr

+XzTZksbZsrTVEmL/Ym+R5w5jBfFnGk7Yw7ndwfQsfNXQb5AZynClFxnX546lcyZX

+fEx3/e6ezw57WNOUK6WT+8b+EGovPkbetK/rGxNXuWaP6X4A/QUm8O98nCuHYFQq

++mvNdsCBqGf7mhaRGtpHk/JgCn5rFvArMDqLVrR9hX0LdCSsH7EGE+bR3r7wuQEN

+BFjmORgBCACk+vDZrIXQuFXEYToZVwb2attzbbJJCqD71vmZTLsW0QxuPKRgbcYY

+zp4K4lVBnHhFrF8MOUOxJ7kQWIJZMZFt+BDcptCYurbD2H4W2xvnWViiC+LzCMzz

+iMJT6165uefL4JHTDPxC2fFiM9yrc72LmylJNkM/vepT128J5Qv0gRUaQbHiQuS6

+Dm/+WRnUfx3i89SV4mnBxb/Ta93GVqoOciWwzWSnwEnWYAvOb95JL4U7c5J5f/+c

+KnQDHsW7sIiIdscsWzvgf6qs2Ra1Zrt7Fdk4+ZS2f/adagLhDO1C24sXf5XfMk5m

+L0OGwZSr9m5s17VXxfspgU5ugc8kBJfzABEBAAE=

+=WCfs

+-----END PGP PUBLIC KEY BLOCK-----

+

diff --git a/tests/data/keys/CVE-2021-3521-nosubsig-last.asc b/tests/data/keys/CVE-2021-3521-nosubsig-last.asc

new file mode 100644

index 000000000..aea00f9d7

--- /dev/null

+++ b/tests/data/keys/CVE-2021-3521-nosubsig-last.asc

@@ -0,0 +1,25 @@

+-----BEGIN PGP PUBLIC KEY BLOCK-----

+Version: rpm-4.17.90 (NSS-3)

+

+mQENBFjmORgBCAC7TMEk6wnjSs8Dr4yqSScWdU2pjcqrkTxuzdWvowcIUPZI0w/g

+HkRqGd4apjvY2V15kjL10gk3QhFP3pZ/9p7zh8o8NHX7aGdSGDK7NOq1eFaErPRY

+91LW9RiZ0lbOjXEzIL0KHxUiTQEmdXJT43DJMFPyW9fkCWg0OltiX618FUdWWfI8

+eySdLur1utnqBvdEbCUvWK2RX3vQZQdvEBODnNk2pxqTyV0w6VPQ96W++lF/5Aas

+7rUv3HIyIXxIggc8FRrnH+y9XvvHDonhTIlGnYZN4ubm9i4y3gOkrZlGTrEw7elQ

+1QeMyG2QQEbze8YjpTm4iLABCBrRfPRaQpwrABEBAAG0IXJwbS5vcmcgUlNBIHRl

+c3RrZXkgPHJzYUBycG0ub3JnPokBNwQTAQgAIQUCWOY5GAIbAwULCQgHAgYVCAkK

+CwIEFgIDAQIeAQIXgAAKCRBDRFkeGWTF/MxxCACnjqFL+MmPh9W9JQKT2DcLbBzf

+Cqo6wcEBoCOcwgRSk8dSikhARoteoa55JRJhuMyeKhhEAogE9HRmCPFdjezFTwgB

+BDVBpO2dZ023mLXDVCYX3S8pShOgCP6Tn4wqCnYeAdLcGg106N4xcmgtcssJE+Pr

+XzTZksbZsrTVEmL/Ym+R5w5jBfFnGk7Yw7ndwfQsfNXQb5AZynClFxnX546lcyZX

+fEx3/e6ezw57WNOUK6WT+8b+EGovPkbetK/rGxNXuWaP6X4A/QUm8O98nCuHYFQq

++mvNdsCBqGf7mhaRGtpHk/JgCn5rFvArMDqLVrR9hX0LdCSsH7EGE+bR3r7wuQEN

+BFjmORgBCACk+vDZrIXQuFXEYToZVwb2attzbbJJCqD71vmZTLsW0QxuPKRgbcYY

+zp4K4lVBnHhFrF8MOUOxJ7kQWIJZMZFt+BDcptCYurbD2H4W2xvnWViiC+LzCMzz

+iMJT6165uefL4JHTDPxC2fFiM9yrc72LmylJNkM/vepT128J5Qv0gRUaQbHiQuS6

+Dm/+WRnUfx3i89SV4mnBxb/Ta93GVqoOciWwzWSnwEnWYAvOb95JL4U7c5J5f/+c

+KnQDHsW7sIiIdscsWzvgf6qs2Ra1Zrt7Fdk4+ZS2f/adagLhDO1C24sXf5XfMk5m

+L0OGwZSr9m5s17VXxfspgU5ugc8kBJfzABEBAAE=

+=WCfs

+-----END PGP PUBLIC KEY BLOCK-----

+

diff --git a/tests/data/keys/CVE-2021-3521-nosubsig.asc b/tests/data/keys/CVE-2021-3521-nosubsig.asc

new file mode 100644

index 000000000..3a2e7417f

--- /dev/null

+++ b/tests/data/keys/CVE-2021-3521-nosubsig.asc

@@ -0,0 +1,37 @@

+-----BEGIN PGP PUBLIC KEY BLOCK-----

+Version: rpm-4.17.90 (NSS-3)

+

+mQENBFjmORgBCAC7TMEk6wnjSs8Dr4yqSScWdU2pjcqrkTxuzdWvowcIUPZI0w/g

+HkRqGd4apjvY2V15kjL10gk3QhFP3pZ/9p7zh8o8NHX7aGdSGDK7NOq1eFaErPRY

+91LW9RiZ0lbOjXEzIL0KHxUiTQEmdXJT43DJMFPyW9fkCWg0OltiX618FUdWWfI8

+eySdLur1utnqBvdEbCUvWK2RX3vQZQdvEBODnNk2pxqTyV0w6VPQ96W++lF/5Aas

+7rUv3HIyIXxIggc8FRrnH+y9XvvHDonhTIlGnYZN4ubm9i4y3gOkrZlGTrEw7elQ

+1QeMyG2QQEbze8YjpTm4iLABCBrRfPRaQpwrABEBAAG0IXJwbS5vcmcgUlNBIHRl

+c3RrZXkgPHJzYUBycG0ub3JnPokBNwQTAQgAIQUCWOY5GAIbAwULCQgHAgYVCAkK

+CwIEFgIDAQIeAQIXgAAKCRBDRFkeGWTF/MxxCACnjqFL+MmPh9W9JQKT2DcLbBzf

+Cqo6wcEBoCOcwgRSk8dSikhARoteoa55JRJhuMyeKhhEAogE9HRmCPFdjezFTwgB

+BDVBpO2dZ023mLXDVCYX3S8pShOgCP6Tn4wqCnYeAdLcGg106N4xcmgtcssJE+Pr

+XzTZksbZsrTVEmL/Ym+R5w5jBfFnGk7Yw7ndwfQsfNXQb5AZynClFxnX546lcyZX

+fEx3/e6ezw57WNOUK6WT+8b+EGovPkbetK/rGxNXuWaP6X4A/QUm8O98nCuHYFQq

++mvNdsCBqGf7mhaRGtpHk/JgCn5rFvArMDqLVrR9hX0LdCSsH7EGE+bR3r7wuQEN

+BFjmORgBCACk+vDZrIXQuFXEYToZVwb2attzbbJJCqD71vmZTLsW0QxuPKRgbcYY

+zp4K4lVBnHhFrF8MOUOxJ7kQWIJZMZFt+BDcptCYurbD2H4W2xvnWViiC+LzCMzz

+iMJT6165uefL4JHTDPxC2fFiM9yrc72LmylJNkM/vepT128J5Qv0gRUaQbHiQuS6

+Dm/+WRnUfx3i89SV4mnBxb/Ta93GVqoOciWwzWSnwEnWYAvOb95JL4U7c5J5f/+c

+KnQDHsW7sIiIdscsWzvgf6qs2Ra1Zrt7Fdk4+ZS2f/adagLhDO1C24sXf5XfMk5m

+L0OGwZSr9m5s17VXxfspgU5ugc8kBJfzABEBAAG5AQ0EWOY5GAEIAKT68NmshdC4

+VcRhOhlXBvZq23NtskkKoPvW+ZlMuxbRDG48pGBtxhjOngriVUGceEWsXww5Q7En

+uRBYglkxkW34ENym0Ji6tsPYfhbbG+dZWKIL4vMIzPOIwlPrXrm558vgkdMM/ELZ

+8WIz3KtzvYubKUk2Qz+96lPXbwnlC/SBFRpBseJC5LoOb/5ZGdR/HeLz1JXiacHF

+v9Nr3cZWqg5yJbDNZKfASdZgC85v3kkvhTtzknl//5wqdAMexbuwiIh2xyxbO+B/

+qqzZFrVmu3sV2Tj5lLZ/9p1qAuEM7ULbixd/ld8yTmYvQ4bBlKv2bmzXtVfF+ymB

+Tm6BzyQEl/MAEQEAAYkBHwQYAQgACQUCWOY5GAIbDAAKCRBDRFkeGWTF/PANB/9j

+mifmj6z/EPe0PJFhrpISt9PjiUQCt0IPtiL5zKAkWjHePIzyi+0kCTBF6DDLFxos

+3vN4bWnVKT1kBhZAQlPqpJTg+m74JUYeDGCdNx9SK7oRllATqyu+5rncgxjWVPnQ

+zu/HRPlWJwcVFYEVXYL8xzfantwQTqefjmcRmBRdA2XJITK+hGWwAmrqAWx+q5xX

+Pa8wkNMxVzNS2rUKO9SoVuJ/wlUvfoShkJ/VJ5HDp3qzUqncADfdGN35TDzscngQ

+gHvnMwVBfYfSCABV1hNByoZcc/kxkrWMmsd/EnIyLd1Q1baKqc3cEDuC6E6/o4yJ

+E4XX4jtDmdZPreZALsiB

+=rRop

+-----END PGP PUBLIC KEY BLOCK-----

+

diff --git a/tests/rpmsigdig.at b/tests/rpmsigdig.at

index e1a3ab062..705fc5870 100644

--- a/tests/rpmsigdig.at

+++ b/tests/rpmsigdig.at

@@ -240,6 +240,34 @@ gpg(185e6146f00650f8) = 4:185e6146f00650f8-58e63918

 [])

 AT_CLEANUP

+AT_SETUP([rpmkeys --import invalid keys])

+AT_KEYWORDS([rpmkeys import])

+RPMDB_INIT

+

+AT_CHECK([

+runroot rpmkeys --import /data/keys/CVE-2021-3521-badbind.asc

+],

+[1],

+[],

+[error: /data/keys/CVE-2021-3521-badbind.asc: key 1 import failed.]

+)

+AT_CHECK([

+runroot rpmkeys --import /data/keys/CVE-2021-3521-nosubsig.asc

+],

+[1],

+[],

+[error: /data/keys/CVE-2021-3521-nosubsig.asc: key 1 import failed.]

+)

+

+AT_CHECK([

+runroot rpmkeys --import /data/keys/CVE-2021-3521-nosubsig-last.asc

+],

+[1],

+[],

+[error: /data/keys/CVE-2021-3521-nosubsig-last.asc: key 1 import failed.]

+)

+AT_CLEANUP

+

 # ------------------------------

 # Test pre-built package verification

 AT_SETUP([rpmkeys -K <signed> 1])

-- 

2.34.1