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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 <rsalz@openssl.org>
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mattcaswell committed May 5, 2016
1 parent f792c66 commit a004e72b95835136d3f1ea90517f706c24c03da7
Showing with 38 additions and 34 deletions.
  1. +7 −7 ssl/s3_srvr.c
  2. +1 −1 ssl/ssl_sess.c
  3. +30 −26 ssl/t1_lib.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);
@@ -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;
}
@@ -1867,27 +1867,27 @@ 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);

if (type != TLSEXT_TYPE_server_name)
return;

if (data + size > limit)
if (limit - data < size)
return;
data += size;

if (TLS1_get_client_version(s) >= TLS1_2_VERSION) {
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;

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