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Limit ASN.1 constructed types recursive definition depth

Constructed types with a recursive definition (such as can be found in
PKCS7) could eventually exceed the stack given malicious input with
excessive recursion. Therefore we limit the stack depth.

CVE-2018-0739

Credit to OSSFuzz for finding this issue.

Reviewed-by: Rich Salz <rsalz@openssl.org>
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mattcaswell committed Mar 22, 2018
1 parent 3ffc95b commit 9310d45087ae546e27e61ddf8f6367f29848220d
Showing with 44 additions and 22 deletions.
  1. +1 −0 crypto/asn1/asn1.h
  2. +2 −1 crypto/asn1/asn1_err.c
  3. +41 −21 crypto/asn1/tasn_dec.c
@@ -1365,6 +1365,7 @@ void ERR_load_ASN1_strings(void);
# define ASN1_R_MSTRING_NOT_UNIVERSAL 139
# define ASN1_R_MSTRING_WRONG_TAG 140
# define ASN1_R_NESTED_ASN1_STRING 197
# define ASN1_R_NESTED_TOO_DEEP 219
# define ASN1_R_NON_HEX_CHARACTERS 141
# define ASN1_R_NOT_ASCII_FORMAT 190
# define ASN1_R_NOT_ENOUGH_DATA 142
@@ -1,6 +1,6 @@
/* crypto/asn1/asn1_err.c */
/* ====================================================================
* Copyright (c) 1999-2014 The OpenSSL Project. All rights reserved.
* Copyright (c) 1999-2018 The OpenSSL Project. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
@@ -279,6 +279,7 @@ static ERR_STRING_DATA ASN1_str_reasons[] = {
{ERR_REASON(ASN1_R_MSTRING_NOT_UNIVERSAL), "mstring not universal"},
{ERR_REASON(ASN1_R_MSTRING_WRONG_TAG), "mstring wrong tag"},
{ERR_REASON(ASN1_R_NESTED_ASN1_STRING), "nested asn1 string"},
{ERR_REASON(ASN1_R_NESTED_TOO_DEEP), "nested too deep"},
{ERR_REASON(ASN1_R_NON_HEX_CHARACTERS), "non hex characters"},
{ERR_REASON(ASN1_R_NOT_ASCII_FORMAT), "not ascii format"},
{ERR_REASON(ASN1_R_NOT_ENOUGH_DATA), "not enough data"},
@@ -65,6 +65,14 @@
#include <openssl/buffer.h>
#include <openssl/err.h>

/*
* Constructed types with a recursive definition (such as can be found in PKCS7)
* could eventually exceed the stack given malicious input with excessive
* recursion. Therefore we limit the stack depth. This is the maximum number of
* recursive invocations of asn1_item_embed_d2i().
*/
#define ASN1_MAX_CONSTRUCTED_NEST 30

static int asn1_check_eoc(const unsigned char **in, long len);
static int asn1_find_end(const unsigned char **in, long len, char inf);

@@ -81,11 +89,11 @@ static int asn1_check_tlen(long *olen, int *otag, unsigned char *oclass,
static int asn1_template_ex_d2i(ASN1_VALUE **pval,
const unsigned char **in, long len,
const ASN1_TEMPLATE *tt, char opt,
ASN1_TLC *ctx);
ASN1_TLC *ctx, int depth);
static int asn1_template_noexp_d2i(ASN1_VALUE **val,
const unsigned char **in, long len,
const ASN1_TEMPLATE *tt, char opt,
ASN1_TLC *ctx);
ASN1_TLC *ctx, int depth);
static int asn1_d2i_ex_primitive(ASN1_VALUE **pval,
const unsigned char **in, long len,
const ASN1_ITEM *it,
@@ -154,17 +162,16 @@ int ASN1_template_d2i(ASN1_VALUE **pval,
{
ASN1_TLC c;
asn1_tlc_clear_nc(&c);
return asn1_template_ex_d2i(pval, in, len, tt, 0, &c);
return asn1_template_ex_d2i(pval, in, len, tt, 0, &c, 0);
}

/*
* Decode an item, taking care of IMPLICIT tagging, if any. If 'opt' set and
* tag mismatch return -1 to handle OPTIONAL
*/

int ASN1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
const ASN1_ITEM *it,
int tag, int aclass, char opt, ASN1_TLC *ctx)
static int asn1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in,
long len, const ASN1_ITEM *it, int tag, int aclass,
char opt, ASN1_TLC *ctx, int depth)
{
const ASN1_TEMPLATE *tt, *errtt = NULL;
const ASN1_COMPAT_FUNCS *cf;
@@ -189,6 +196,11 @@ int ASN1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
else
asn1_cb = 0;

if (++depth > ASN1_MAX_CONSTRUCTED_NEST) {
ASN1err(ASN1_F_ASN1_ITEM_EX_D2I, ASN1_R_NESTED_TOO_DEEP);
goto err;
}

switch (it->itype) {
case ASN1_ITYPE_PRIMITIVE:
if (it->templates) {
@@ -204,7 +216,7 @@ int ASN1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
goto err;
}
return asn1_template_ex_d2i(pval, in, len,
it->templates, opt, ctx);
it->templates, opt, ctx, depth);
}
return asn1_d2i_ex_primitive(pval, in, len, it,
tag, aclass, opt, ctx);
@@ -326,7 +338,7 @@ int ASN1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
/*
* We mark field as OPTIONAL so its absence can be recognised.
*/
ret = asn1_template_ex_d2i(pchptr, &p, len, tt, 1, ctx);
ret = asn1_template_ex_d2i(pchptr, &p, len, tt, 1, ctx, depth);
/* If field not present, try the next one */
if (ret == -1)
continue;
@@ -444,7 +456,8 @@ int ASN1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
* attempt to read in field, allowing each to be OPTIONAL
*/

ret = asn1_template_ex_d2i(pseqval, &p, len, seqtt, isopt, ctx);
ret = asn1_template_ex_d2i(pseqval, &p, len, seqtt, isopt, ctx,
depth);
if (!ret) {
errtt = seqtt;
goto err;
@@ -514,6 +527,13 @@ int ASN1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
return 0;
}

int ASN1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
const ASN1_ITEM *it,
int tag, int aclass, char opt, ASN1_TLC *ctx)
{
return asn1_item_ex_d2i(pval, in, len, it, tag, aclass, opt, ctx, 0);
}

/*
* Templates are handled with two separate functions. One handles any
* EXPLICIT tag and the other handles the rest.
@@ -522,7 +542,7 @@ int ASN1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
static int asn1_template_ex_d2i(ASN1_VALUE **val,
const unsigned char **in, long inlen,
const ASN1_TEMPLATE *tt, char opt,
ASN1_TLC *ctx)
ASN1_TLC *ctx, int depth)
{
int flags, aclass;
int ret;
@@ -557,7 +577,7 @@ static int asn1_template_ex_d2i(ASN1_VALUE **val,
return 0;
}
/* We've found the field so it can't be OPTIONAL now */
ret = asn1_template_noexp_d2i(val, &p, len, tt, 0, ctx);
ret = asn1_template_noexp_d2i(val, &p, len, tt, 0, ctx, depth);
if (!ret) {
ASN1err(ASN1_F_ASN1_TEMPLATE_EX_D2I, ERR_R_NESTED_ASN1_ERROR);
return 0;
@@ -581,7 +601,7 @@ static int asn1_template_ex_d2i(ASN1_VALUE **val,
}
}
} else
return asn1_template_noexp_d2i(val, in, inlen, tt, opt, ctx);
return asn1_template_noexp_d2i(val, in, inlen, tt, opt, ctx, depth);

*in = p;
return 1;
@@ -594,7 +614,7 @@ static int asn1_template_ex_d2i(ASN1_VALUE **val,
static int asn1_template_noexp_d2i(ASN1_VALUE **val,
const unsigned char **in, long len,
const ASN1_TEMPLATE *tt, char opt,
ASN1_TLC *ctx)
ASN1_TLC *ctx, int depth)
{
int flags, aclass;
int ret;
@@ -665,8 +685,8 @@ static int asn1_template_noexp_d2i(ASN1_VALUE **val,
break;
}
skfield = NULL;
if (!ASN1_item_ex_d2i(&skfield, &p, len,
ASN1_ITEM_ptr(tt->item), -1, 0, 0, ctx)) {
if (!asn1_item_ex_d2i(&skfield, &p, len, ASN1_ITEM_ptr(tt->item),
-1, 0, 0, ctx, depth)) {
ASN1err(ASN1_F_ASN1_TEMPLATE_NOEXP_D2I,
ERR_R_NESTED_ASN1_ERROR);
goto err;
@@ -684,18 +704,18 @@ static int asn1_template_noexp_d2i(ASN1_VALUE **val,
}
} else if (flags & ASN1_TFLG_IMPTAG) {
/* IMPLICIT tagging */
ret = ASN1_item_ex_d2i(val, &p, len,
ASN1_ITEM_ptr(tt->item), tt->tag, aclass, opt,
ctx);
ret = asn1_item_ex_d2i(val, &p, len, ASN1_ITEM_ptr(tt->item), tt->tag,
aclass, opt, ctx, depth);
if (!ret) {
ASN1err(ASN1_F_ASN1_TEMPLATE_NOEXP_D2I, ERR_R_NESTED_ASN1_ERROR);
goto err;
} else if (ret == -1)
return -1;
} else {
/* Nothing special */
ret = ASN1_item_ex_d2i(val, &p, len, ASN1_ITEM_ptr(tt->item),
-1, tt->flags & ASN1_TFLG_COMBINE, opt, ctx);
ret = asn1_item_ex_d2i(val, &p, len, ASN1_ITEM_ptr(tt->item),
-1, tt->flags & ASN1_TFLG_COMBINE, opt, ctx,
depth);
if (!ret) {
ASN1err(ASN1_F_ASN1_TEMPLATE_NOEXP_D2I, ERR_R_NESTED_ASN1_ERROR);
goto err;

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