Check that multi-strings/CHOICE types don't use implicit tagging

It never makes sense for multi-string or CHOICE types to use implicit tagging since the content would be ambiguous. It is an error in the template if this ever happens. If we detect it we should stop parsing. Thanks to David Benjamin from Google for reporting this issue. Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
openssl · Dec 8, 2020 · 1ecc76f · 1ecc76f
1 parent f960d81
commit 1ecc76f
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diff --git a/crypto/asn1/asn1_err.c b/crypto/asn1/asn1_err.c
@@ -160,6 +160,7 @@ static const ERR_STRING_DATA ASN1_str_reasons[] = {
     "asn1 sig parse error"},
     {ERR_PACK(ERR_LIB_ASN1, 0, ASN1_R_AUX_ERROR), "aux error"},
     {ERR_PACK(ERR_LIB_ASN1, 0, ASN1_R_BAD_OBJECT_HEADER), "bad object header"},
+    {ERR_PACK(ERR_LIB_ASN1, 0, ASN1_R_BAD_TEMPLATE), "bad template"},
     {ERR_PACK(ERR_LIB_ASN1, 0, ASN1_R_BMPSTRING_IS_WRONG_LENGTH),
     "bmpstring is wrong length"},
     {ERR_PACK(ERR_LIB_ASN1, 0, ASN1_R_BN_LIB), "bn lib"},

diff --git a/crypto/asn1/tasn_dec.c b/crypto/asn1/tasn_dec.c
@@ -182,6 +182,15 @@ static int asn1_item_embed_d2i(ASN1_VALUE **pval, const unsigned char **in,
                                      tag, aclass, opt, ctx);
 
     case ASN1_ITYPE_MSTRING:
+        /*
+         * It never makes sense for multi-strings to have implicit tagging, so
+         * if tag != -1, then this looks like an error in the template.
+         */
+        if (tag != -1) {
+            ASN1err(ASN1_F_ASN1_ITEM_EMBED_D2I, ASN1_R_BAD_TEMPLATE);
+            goto err;
+        }
+
         p = *in;
         /* Just read in tag and class */
         ret = asn1_check_tlen(NULL, &otag, &oclass, NULL, NULL,
@@ -199,6 +208,7 @@ static int asn1_item_embed_d2i(ASN1_VALUE **pval, const unsigned char **in,
             ASN1err(ASN1_F_ASN1_ITEM_EMBED_D2I, ASN1_R_MSTRING_NOT_UNIVERSAL);
             goto err;
         }
+
         /* Check tag matches bit map */
         if (!(ASN1_tag2bit(otag) & it->utype)) {
             /* If OPTIONAL, assume this is OK */
@@ -215,6 +225,15 @@ static int asn1_item_embed_d2i(ASN1_VALUE **pval, const unsigned char **in,
         return ef->asn1_ex_d2i(pval, in, len, it, tag, aclass, opt, ctx);
 
     case ASN1_ITYPE_CHOICE:
+        /*
+         * It never makes sense for CHOICE types to have implicit tagging, so
+         * if tag != -1, then this looks like an error in the template.
+         */
+        if (tag != -1) {
+            ASN1err(ASN1_F_ASN1_ITEM_EMBED_D2I, ASN1_R_BAD_TEMPLATE);
+            goto err;
+        }
+
         if (asn1_cb && !asn1_cb(ASN1_OP_D2I_PRE, pval, it, NULL))
             goto auxerr;
         if (*pval) {

diff --git a/crypto/err/openssl.txt b/crypto/err/openssl.txt
@@ -1771,6 +1771,7 @@ ASN1_R_ASN1_PARSE_ERROR:203:asn1 parse error
 ASN1_R_ASN1_SIG_PARSE_ERROR:204:asn1 sig parse error
 ASN1_R_AUX_ERROR:100:aux error
 ASN1_R_BAD_OBJECT_HEADER:102:bad object header
+ASN1_R_BAD_TEMPLATE:230:bad template
 ASN1_R_BMPSTRING_IS_WRONG_LENGTH:214:bmpstring is wrong length
 ASN1_R_BN_LIB:105:bn lib
 ASN1_R_BOOLEAN_IS_WRONG_LENGTH:106:boolean is wrong length

diff --git a/include/openssl/asn1err.h b/include/openssl/asn1err.h
@@ -145,6 +145,7 @@ int ERR_load_ASN1_strings(void);
 # define ASN1_R_ASN1_SIG_PARSE_ERROR                      204
 # define ASN1_R_AUX_ERROR                                 100
 # define ASN1_R_BAD_OBJECT_HEADER                         102
+# define ASN1_R_BAD_TEMPLATE                              230
 # define ASN1_R_BMPSTRING_IS_WRONG_LENGTH                 214
 # define ASN1_R_BN_LIB                                    105
 # define ASN1_R_BOOLEAN_IS_WRONG_LENGTH                   106