From 01ee1b3b3c665bf22e06b92afa832ccc54de5119 Mon Sep 17 00:00:00 2001 From: Tim Ruffing Date: Wed, 7 Nov 2018 16:07:33 +0100 Subject: [PATCH] Parse DER-enconded length into a size_t instead of an int This avoids a possibly implementation-defined signed (int) to unsigned (size_t) conversion portably. --- src/ecdsa_impl.h | 55 +++++++++++++++++++++++++++--------------------- 1 file changed, 31 insertions(+), 24 deletions(-) diff --git a/src/ecdsa_impl.h b/src/ecdsa_impl.h index 4f62198b85206..2a9b94a607a8b 100644 --- a/src/ecdsa_impl.h +++ b/src/ecdsa_impl.h @@ -46,68 +46,73 @@ static const secp256k1_fe secp256k1_ecdsa_const_p_minus_order = SECP256K1_FE_CON 0, 0, 0, 1, 0x45512319UL, 0x50B75FC4UL, 0x402DA172UL, 0x2FC9BAEEUL ); -static int secp256k1_der_read_len(const unsigned char **sigp, const unsigned char *sigend) { - int lenleft, b1; - size_t ret = 0; +static int secp256k1_der_read_len(size_t *len, const unsigned char **sigp, const unsigned char *sigend) { + size_t lenleft; + unsigned char b1; + VERIFY_CHECK(len != NULL); + *len = 0; if (*sigp >= sigend) { - return -1; + return 0; } b1 = *((*sigp)++); if (b1 == 0xFF) { /* X.690-0207 8.1.3.5.c the value 0xFF shall not be used. */ - return -1; + return 0; } if ((b1 & 0x80) == 0) { /* X.690-0207 8.1.3.4 short form length octets */ - return b1; + *len = b1; + return 1; } if (b1 == 0x80) { /* Indefinite length is not allowed in DER. */ - return -1; + return 0; } /* X.690-207 8.1.3.5 long form length octets */ lenleft = b1 & 0x7F; /* lenleft is at least 1 */ - if (lenleft > sigend - *sigp) { - return -1; + if (lenleft > (size_t)(sigend - *sigp)) { + return 0; } if (**sigp == 0) { /* Not the shortest possible length encoding. */ - return -1; + return 0; } - if ((size_t)lenleft > sizeof(size_t)) { + if (lenleft > sizeof(size_t)) { /* The resulting length would exceed the range of a size_t, so * certainly longer than the passed array size. */ - return -1; + return 0; } while (lenleft > 0) { - ret = (ret << 8) | **sigp; + *len = (*len << 8) | **sigp; (*sigp)++; lenleft--; } - if (ret > (size_t)(sigend - *sigp)) { + if (*len > (size_t)(sigend - *sigp)) { /* Result exceeds the length of the passed array. */ - return -1; + return 0; } - if (ret < 128) { + if (*len < 128) { /* Not the shortest possible length encoding. */ - return -1; + return 0; } - return ret; + return 1; } static int secp256k1_der_parse_integer(secp256k1_scalar *r, const unsigned char **sig, const unsigned char *sigend) { int overflow = 0; unsigned char ra[32] = {0}; - int rlen; + size_t rlen; if (*sig == sigend || **sig != 0x02) { /* Not a primitive integer (X.690-0207 8.3.1). */ return 0; } (*sig)++; - rlen = secp256k1_der_read_len(sig, sigend); - if (rlen <= 0 || (*sig) + rlen > sigend) { + if (secp256k1_der_read_len(&rlen, sig, sigend) == 0) { + return 0; + } + if (rlen == 0 || *sig + rlen > sigend) { /* Exceeds bounds or not at least length 1 (X.690-0207 8.3.1). */ return 0; } @@ -144,13 +149,15 @@ static int secp256k1_der_parse_integer(secp256k1_scalar *r, const unsigned char static int secp256k1_ecdsa_sig_parse(secp256k1_scalar *rr, secp256k1_scalar *rs, const unsigned char *sig, size_t size) { const unsigned char *sigend = sig + size; - int rlen; + size_t rlen; if (sig == sigend || *(sig++) != 0x30) { /* The encoding doesn't start with a constructed sequence (X.690-0207 8.9.1). */ return 0; } - rlen = secp256k1_der_read_len(&sig, sigend); - if (rlen < 0 || sig + rlen > sigend) { + if (secp256k1_der_read_len(&rlen, &sig, sigend) == 0) { + return 0; + } + if (sig + rlen > sigend) { /* Tuple exceeds bounds */ return 0; }