Check for potentially exploitable overflows in asn1_d2i_read_bio

BUF_mem_grow and BUF_mem_grow_clean. Refuse attempts to shrink buffer
in CRYPTO_realloc_clean.

Thanks to Tavis Ormandy, Google Security Team, for discovering this
issue and to Adam Langley <agl@chromium.org> for fixing it. (CVE-2012-2110)

CHANGES

@@ -289,7 +289,16 @@
      whose return value is often ignored. 
      [Steve Henson]
   
- Changes between 1.0.1 and 1.0.1a [xx XXX xxxx]
+ Changes between 1.0.1 and 1.0.1a [19 Apr 2012]
+
+  *) Check for potentially exploitable overflows in asn1_d2i_read_bio
+     BUF_mem_grow and BUF_mem_grow_clean. Refuse attempts to shrink buffer
+     in CRYPTO_realloc_clean.
+
+     Thanks to Tavis Ormandy, Google Security Team, for discovering this
+     issue and to Adam Langley <agl@chromium.org> for fixing it.
+     (CVE-2012-2110)
+     [Adam Langley (Google), Tavis Ormandy, Google Security Team]
 
   *) Don't allow TLS 1.2 SHA-256 ciphersuites in TLS 1.0, 1.1 connections.
      [Adam Langley]

crypto/asn1/a_d2i_fp.c

@@ -57,6 +57,7 @@
  */
 
 #include <stdio.h>
+#include <limits.h>
 #include "cryptlib.h"
 #include <openssl/buffer.h>
 #include <openssl/asn1_mac.h>
@@ -143,17 +144,11 @@ static int asn1_d2i_read_bio(BIO *in, BUF_MEM **pb)
 	BUF_MEM *b;
 	unsigned char *p;
 	int i;
-	int ret=-1;
 	ASN1_const_CTX c;
-	int want=HEADER_SIZE;
+	size_t want=HEADER_SIZE;
 	int eos=0;
-#if defined(__GNUC__) && defined(__ia64)
-	/* pathetic compiler bug in all known versions as of Nov. 2002 */
-	long off=0;
-#else
-	int off=0;
-#endif
-	int len=0;
+	size_t off=0;
+	size_t len=0;
 
 	b=BUF_MEM_new();
 	if (b == NULL)
@@ -169,7 +164,7 @@ static int asn1_d2i_read_bio(BIO *in, BUF_MEM **pb)
 			{
 			want-=(len-off);
 
-			if (!BUF_MEM_grow_clean(b,len+want))
+			if (len + want < len || !BUF_MEM_grow_clean(b,len+want))
 				{
 				ASN1err(ASN1_F_ASN1_D2I_READ_BIO,ERR_R_MALLOC_FAILURE);
 				goto err;
@@ -181,7 +176,14 @@ static int asn1_d2i_read_bio(BIO *in, BUF_MEM **pb)
 				goto err;
 				}
 			if (i > 0)
+				{
+				if (len+i < len)
+					{
+					ASN1err(ASN1_F_ASN1_D2I_READ_BIO,ASN1_R_TOO_LONG);
+					goto err;
+					}
 				len+=i;
+				}
 			}
 		/* else data already loaded */
 
@@ -206,6 +208,11 @@ static int asn1_d2i_read_bio(BIO *in, BUF_MEM **pb)
 			{
 			/* no data body so go round again */
 			eos++;
+			if (eos < 0)
+				{
+				ASN1err(ASN1_F_ASN1_D2I_READ_BIO,ASN1_R_HEADER_TOO_LONG);
+				goto err;
+				}
 			want=HEADER_SIZE;
 			}
 		else if (eos && (c.slen == 0) && (c.tag == V_ASN1_EOC))
@@ -220,10 +227,16 @@ static int asn1_d2i_read_bio(BIO *in, BUF_MEM **pb)
 		else 
 			{
 			/* suck in c.slen bytes of data */
-			want=(int)c.slen;
+			want=c.slen;
 			if (want > (len-off))
 				{
 				want-=(len-off);
+				if (want > INT_MAX /* BIO_read takes an int length */ ||
+					len+want < len)
+						{
+						ASN1err(ASN1_F_ASN1_D2I_READ_BIO,ASN1_R_TOO_LONG);
+						goto err;
+						}
 				if (!BUF_MEM_grow_clean(b,len+want))
 					{
 					ASN1err(ASN1_F_ASN1_D2I_READ_BIO,ERR_R_MALLOC_FAILURE);
@@ -238,11 +251,18 @@ static int asn1_d2i_read_bio(BIO *in, BUF_MEM **pb)
 						    ASN1_R_NOT_ENOUGH_DATA);
 						goto err;
 						}
+					/* This can't overflow because
+					 * |len+want| didn't overflow. */
 					len+=i;
-					want -= i;
+					want-=i;
 					}
 				}
-			off+=(int)c.slen;
+			if (off + c.slen < off)
+				{
+				ASN1err(ASN1_F_ASN1_D2I_READ_BIO,ASN1_R_TOO_LONG);
+				goto err;
+				}
+			off+=c.slen;
 			if (eos <= 0)
 				{
 				break;
@@ -252,9 +272,15 @@ static int asn1_d2i_read_bio(BIO *in, BUF_MEM **pb)
 			}
 		}
 
+	if (off > INT_MAX)
+		{
+		ASN1err(ASN1_F_ASN1_D2I_READ_BIO,ASN1_R_TOO_LONG);
+		goto err;
+		}
+
 	*pb = b;
 	return off;
 err:
 	if (b != NULL) BUF_MEM_free(b);
-	return(ret);
+	return -1;
 	}

crypto/buffer/buffer.c

@@ -60,6 +60,11 @@
 #include "cryptlib.h"
 #include <openssl/buffer.h>
 
+/* LIMIT_BEFORE_EXPANSION is the maximum n such that (n+3)/3*4 < 2**31. That
+ * function is applied in several functions in this file and this limit ensures
+ * that the result fits in an int. */
+#define LIMIT_BEFORE_EXPANSION 0x5ffffffc
+
 BUF_MEM *BUF_MEM_new(void)
 	{
 	BUF_MEM *ret;
@@ -105,6 +110,12 @@ int BUF_MEM_grow(BUF_MEM *str, size_t len)
 		str->length=len;
 		return(len);
 		}
+	/* This limit is sufficient to ensure (len+3)/3*4 < 2**31 */
+	if (len > LIMIT_BEFORE_EXPANSION)
+		{
+		BUFerr(BUF_F_BUF_MEM_GROW,ERR_R_MALLOC_FAILURE);
+		return 0;
+		}
 	n=(len+3)/3*4;
 	if (str->data == NULL)
 		ret=OPENSSL_malloc(n);
@@ -142,6 +153,12 @@ int BUF_MEM_grow_clean(BUF_MEM *str, size_t len)
 		str->length=len;
 		return(len);
 		}
+	/* This limit is sufficient to ensure (len+3)/3*4 < 2**31 */
+	if (len > LIMIT_BEFORE_EXPANSION)
+		{
+		BUFerr(BUF_F_BUF_MEM_GROW,ERR_R_MALLOC_FAILURE);
+		return 0;
+		}
 	n=(len+3)/3*4;
 	if (str->data == NULL)
 		ret=OPENSSL_malloc(n);

crypto/mem.c

@@ -364,6 +364,10 @@ void *CRYPTO_realloc_clean(void *str, int old_len, int num, const char *file,
 
 	if (num <= 0) return NULL;
 
+	/* We don't support shrinking the buffer. Note the memcpy that copies
+	 * |old_len| bytes to the new buffer, below. */
+	if (num < old_len) return NULL;
+
 	if (realloc_debug_func != NULL)
 		realloc_debug_func(str, NULL, num, file, line, 0);
 	ret=malloc_ex_func(num,file,line);