From a004e72b95835136d3f1ea90517f706c24c03da7 Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Thu, 5 May 2016 11:10:26 +0100 Subject: [PATCH] Avoid some undefined pointer arithmetic A common idiom in the codebase is: if (p + len > limit) { return; /* Too long */ } Where "p" points to some malloc'd data of SIZE bytes and limit == p + SIZE "len" here could be from some externally supplied data (e.g. from a TLS message). The rules of C pointer arithmetic are such that "p + len" is only well defined where len <= SIZE. Therefore the above idiom is actually undefined behaviour. For example this could cause problems if some malloc implementation provides an address for "p" such that "p + len" actually overflows for values of len that are too big and therefore p + len < limit! Issue reported by Guido Vranken. CVE-2016-2177 Reviewed-by: Rich Salz --- ssl/s3_srvr.c | 14 ++++++------- ssl/ssl_sess.c | 2 +- ssl/t1_lib.c | 56 +++++++++++++++++++++++++++----------------------- 3 files changed, 38 insertions(+), 34 deletions(-) diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c index ab28702ee9..ab7f6900d2 100644 --- a/ssl/s3_srvr.c +++ b/ssl/s3_srvr.c @@ -980,7 +980,7 @@ int ssl3_get_client_hello(SSL *s) session_length = *(p + SSL3_RANDOM_SIZE); - if (p + SSL3_RANDOM_SIZE + session_length + 1 >= d + n) { + if (SSL3_RANDOM_SIZE + session_length + 1 >= (d + n) - p) { al = SSL_AD_DECODE_ERROR; SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT); goto f_err; @@ -998,7 +998,7 @@ int ssl3_get_client_hello(SSL *s) /* get the session-id */ j = *(p++); - if (p + j > d + n) { + if ((d + n) - p < j) { al = SSL_AD_DECODE_ERROR; SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT); goto f_err; @@ -1054,14 +1054,14 @@ int ssl3_get_client_hello(SSL *s) if (SSL_IS_DTLS(s)) { /* cookie stuff */ - if (p + 1 > d + n) { + if ((d + n) - p < 1) { al = SSL_AD_DECODE_ERROR; SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT); goto f_err; } cookie_len = *(p++); - if (p + cookie_len > d + n) { + if ((d + n ) - p < cookie_len) { al = SSL_AD_DECODE_ERROR; SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT); goto f_err; @@ -1131,7 +1131,7 @@ int ssl3_get_client_hello(SSL *s) } } - if (p + 2 > d + n) { + if ((d + n ) - p < 2) { al = SSL_AD_DECODE_ERROR; SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT); goto f_err; @@ -1145,7 +1145,7 @@ int ssl3_get_client_hello(SSL *s) } /* i bytes of cipher data + 1 byte for compression length later */ - if ((p + i + 1) > (d + n)) { + if ((d + n) - p < i + 1) { /* not enough data */ al = SSL_AD_DECODE_ERROR; SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH); @@ -1211,7 +1211,7 @@ int ssl3_get_client_hello(SSL *s) /* compression */ i = *(p++); - if ((p + i) > (d + n)) { + if ((d + n) - p < i) { /* not enough data */ al = SSL_AD_DECODE_ERROR; SSLerr(SSL_F_SSL3_GET_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH); diff --git a/ssl/ssl_sess.c b/ssl/ssl_sess.c index b182998343..54ee78350b 100644 --- a/ssl/ssl_sess.c +++ b/ssl/ssl_sess.c @@ -573,7 +573,7 @@ int ssl_get_prev_session(SSL *s, unsigned char *session_id, int len, int r; #endif - if (session_id + len > limit) { + if (limit - session_id < len) { fatal = 1; goto err; } diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c index fb64607acf..cdac0118ca 100644 --- a/ssl/t1_lib.c +++ b/ssl/t1_lib.c @@ -1867,11 +1867,11 @@ static void ssl_check_for_safari(SSL *s, const unsigned char *data, 0x02, 0x03, /* SHA-1/ECDSA */ }; - if (data >= (limit - 2)) + if (limit - data <= 2) return; data += 2; - if (data > (limit - 4)) + if (limit - data < 4) return; n2s(data, type); n2s(data, size); @@ -1879,7 +1879,7 @@ static void ssl_check_for_safari(SSL *s, const unsigned char *data, if (type != TLSEXT_TYPE_server_name) return; - if (data + size > limit) + if (limit - data < size) return; data += size; @@ -1887,7 +1887,7 @@ static void ssl_check_for_safari(SSL *s, const unsigned char *data, const size_t len1 = sizeof(kSafariExtensionsBlock); const size_t len2 = sizeof(kSafariTLS12ExtensionsBlock); - if (data + len1 + len2 != limit) + if (limit - data != (int)(len1 + len2)) return; if (memcmp(data, kSafariExtensionsBlock, len1) != 0) return; @@ -1896,7 +1896,7 @@ static void ssl_check_for_safari(SSL *s, const unsigned char *data, } else { const size_t len = sizeof(kSafariExtensionsBlock); - if (data + len != limit) + if (limit - data != (int)(len)) return; if (memcmp(data, kSafariExtensionsBlock, len) != 0) return; @@ -2053,19 +2053,19 @@ static int ssl_scan_clienthello_tlsext(SSL *s, unsigned char **p, if (data == limit) goto ri_check; - if (data > (limit - 2)) + if (limit - data < 2) goto err; n2s(data, len); - if (data + len != limit) + if (limit - data != len) goto err; - while (data <= (limit - 4)) { + while (limit - data >= 4) { n2s(data, type); n2s(data, size); - if (data + size > (limit)) + if (limit - data < size) goto err; # if 0 fprintf(stderr, "Received extension type %d size %d\n", type, size); @@ -2472,18 +2472,18 @@ static int ssl_scan_clienthello_custom_tlsext(SSL *s, if (s->hit || s->cert->srv_ext.meths_count == 0) return 1; - if (data >= limit - 2) + if (limit - data <= 2) return 1; n2s(data, len); - if (data > limit - len) + if (limit - data < len) return 1; - while (data <= limit - 4) { + while (limit - data >= 4) { n2s(data, type); n2s(data, size); - if (data + size > limit) + if (limit - data < size) return 1; if (custom_ext_parse(s, 1 /* server */ , type, data, size, al) <= 0) return 0; @@ -2569,20 +2569,20 @@ static int ssl_scan_serverhello_tlsext(SSL *s, unsigned char **p, SSL_TLSEXT_HB_DONT_SEND_REQUESTS); # endif - if (data >= (d + n - 2)) + if ((d + n) - data <= 2) goto ri_check; n2s(data, length); - if (data + length != d + n) { + if ((d + n) - data != length) { *al = SSL_AD_DECODE_ERROR; return 0; } - while (data <= (d + n - 4)) { + while ((d + n) - data >= 4) { n2s(data, type); n2s(data, size); - if (data + size > (d + n)) + if ((d + n) - data < size) goto ri_check; if (s->tlsext_debug_cb) @@ -3307,29 +3307,33 @@ int tls1_process_ticket(SSL *s, unsigned char *session_id, int len, /* Skip past DTLS cookie */ if (SSL_IS_DTLS(s)) { i = *(p++); - p += i; - if (p >= limit) + + if (limit - p <= i) return -1; + + p += i; } /* Skip past cipher list */ n2s(p, i); - p += i; - if (p >= limit) + if (limit - p <= i) return -1; + p += i; + /* Skip past compression algorithm list */ i = *(p++); - p += i; - if (p > limit) + if (limit - p < i) return -1; + p += i; + /* Now at start of extensions */ - if ((p + 2) >= limit) + if (limit - p <= 2) return 0; n2s(p, i); - while ((p + 4) <= limit) { + while (limit - p >= 4) { unsigned short type, size; n2s(p, type); n2s(p, size); - if (p + size > limit) + if (limit - p < size) return 0; if (type == TLSEXT_TYPE_session_ticket) { int r; -- 2.25.1