119 lines
3.0 KiB
Diff
119 lines
3.0 KiB
Diff
From: Peter Stuge <peter@stuge.se>
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Date: Sun, 6 Dec 2009 06:20:58 +0000 (+0100)
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Subject: Fix padding in ssh-dss signature blob encoding
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X-Git-Url: http://git.libssh2.org//gitweb.cgi?p=libssh2.git;a=commitdiff_plain;h=1aba38cd7d2658146675ce1737e5090f879f3068
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Fix padding in ssh-dss signature blob encoding
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DSA signatures consist of two 160-bit integers called r and s. In ssh-dss
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signature blobs r and s are stored directly after each other in binary
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representation, making up a 320-bit (40 byte) string. (See RFC4253 p14.)
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The crypto wrappers in libssh2 would either pack r and s incorrectly, or
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fail, when at least one integer was small enough to be stored in 19 bytes
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or less.
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The patch ensures that r and s are always stored as two 160 bit numbers.
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---
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diff --git a/src/libgcrypt.c b/src/libgcrypt.c
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index ba00284..b06be42 100644
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--- a/src/libgcrypt.c
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+++ b/src/libgcrypt.c
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@@ -424,6 +424,8 @@ _libssh2_dsa_sha1_sign(libssh2_dsa_ctx * dsactx,
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return -1;
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}
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+ memset(sig, 0, 40);
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+
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/* Extract R. */
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data = gcry_sexp_find_token(sig_sexp, "r", 0);
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@@ -433,22 +435,12 @@ _libssh2_dsa_sha1_sign(libssh2_dsa_ctx * dsactx,
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}
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tmp = gcry_sexp_nth_data(data, 1, &size);
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- if (!tmp) {
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- ret = -1;
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- goto out;
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- }
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-
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- if (tmp[0] == '\0') {
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- tmp++;
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- size--;
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- }
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-
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- if (size != 20) {
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+ if (!tmp || size < 1 || size > 20) {
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ret = -1;
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goto out;
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}
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- memcpy(sig, tmp, 20);
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+ memcpy(sig + (20 - size), tmp, size);
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gcry_sexp_release(data);
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@@ -461,22 +453,12 @@ _libssh2_dsa_sha1_sign(libssh2_dsa_ctx * dsactx,
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}
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tmp = gcry_sexp_nth_data(data, 1, &size);
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- if (!tmp) {
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- ret = -1;
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- goto out;
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- }
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-
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- if (tmp[0] == '\0') {
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- tmp++;
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- size--;
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- }
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-
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- if (size != 20) {
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+ if (!tmp || size < 1 || size > 20) {
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ret = -1;
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goto out;
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}
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- memcpy(sig + 20, tmp, 20);
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+ memcpy(sig + 20 + (20 - size), tmp, size);
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ret = 0;
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out:
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diff --git a/src/openssl.c b/src/openssl.c
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index 250ea63..000c9ec 100644
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--- a/src/openssl.c
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+++ b/src/openssl.c
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@@ -420,7 +420,7 @@ _libssh2_dsa_sha1_sign(libssh2_dsa_ctx * dsactx,
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unsigned long hash_len, unsigned char *signature)
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{
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DSA_SIG *sig;
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- int r_len, s_len, rs_pad;
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+ int r_len, s_len;
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(void) hash_len;
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sig = DSA_do_sign(hash, SHA_DIGEST_LENGTH, dsactx);
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@@ -429,15 +429,20 @@ _libssh2_dsa_sha1_sign(libssh2_dsa_ctx * dsactx,
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}
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r_len = BN_num_bytes(sig->r);
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+ if (r_len < 1 || r_len > 20) {
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+ DSA_SIG_free(sig);
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+ return -1;
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+ }
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s_len = BN_num_bytes(sig->s);
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- rs_pad = (2 * SHA_DIGEST_LENGTH) - (r_len + s_len);
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- if (rs_pad < 0) {
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+ if (s_len < 1 || s_len > 20) {
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DSA_SIG_free(sig);
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return -1;
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}
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- BN_bn2bin(sig->r, signature + rs_pad);
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- BN_bn2bin(sig->s, signature + rs_pad + r_len);
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+ memset(signature, 0, 40);
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+
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+ BN_bn2bin(sig->r, signature + (20 - r_len));
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+ BN_bn2bin(sig->s, signature + 20 + (20 - s_len));
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DSA_SIG_free(sig);
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