BN_BLINDING multi-threading fix.

Submitted by: Emilia Kasper (Google)

diff --git a/CHANGES b/CHANGES
index a5da898ddb20b942e6a7a7da94483568341c6811..958362a449d14e4e5d2b265376181659a8536207 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,16 @@
 
  Changes between 0.9.8r and 0.9.8s [xx XXX xxxx]
 
+  *) Fix handling of BN_BLINDING: now BN_BLINDING_invert_ex (rather than
+     BN_BLINDING_invert_ex) calls BN_BLINDING_update, ensuring that concurrent
+     threads won't reuse the same blinding coefficients.
+
+     This also avoids the need to obtain the CRYPTO_LOCK_RSA_BLINDING
+     lock to call BN_BLINDING_invert_ex, and avoids one use of
+     BN_BLINDING_update for each BN_BLINDING structure (previously,
+     the last update always remained unused).
+     [Emilia Käsper (Google)]
+
   *) Fix SSL memory handling for (EC)DH ciphersuites, in particular
      for multi-threaded use of ECDH.
      [Adam Langley (Google)]

diff --git a/crypto/bn/bn_blind.c b/crypto/bn/bn_blind.c
index c11fb4ccc2d3e11619c5ad65c33bef7be73d6793..ca7f996bc8a1234577a59de878be3e3ea5119db5 100644 (file)
--- a/crypto/bn/bn_blind.c
+++ b/crypto/bn/bn_blind.c
@@ -123,7 +123,7 @@ struct bn_blinding_st
        BIGNUM *mod; /* just a reference */
        unsigned long thread_id; /* added in OpenSSL 0.9.6j and 0.9.7b;
                                  * used only by crypto/rsa/rsa_eay.c, rsa_lib.c */
-       unsigned int  counter;
+       int counter;
        unsigned long flags;
        BN_MONT_CTX *m_ctx;
        int (*bn_mod_exp)(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
@@ -157,7 +157,10 @@ BN_BLINDING *BN_BLINDING_new(const BIGNUM *A, const BIGNUM *Ai, /* const */ BIGN
        if (BN_get_flags(mod, BN_FLG_CONSTTIME) != 0)
                BN_set_flags(ret->mod, BN_FLG_CONSTTIME);
 
-       ret->counter = BN_BLINDING_COUNTER;
+       /* Set the counter to the special value -1
+        * to indicate that this is never-used fresh blinding
+        * that does not need updating before first use. */
+       ret->counter = -1;
        return(ret);
 err:
        if (ret != NULL) BN_BLINDING_free(ret);
@@ -186,7 +189,10 @@ int BN_BLINDING_update(BN_BLINDING *b, BN_CTX *ctx)
                goto err;
                }
 
-       if (--(b->counter) == 0 && b->e != NULL &&
+       if (b->counter == -1)
+               b->counter = 0;
+
+       if (++b->counter == BN_BLINDING_COUNTER && b->e != NULL &&
                !(b->flags & BN_BLINDING_NO_RECREATE))
                {
                /* re-create blinding parameters */
@@ -201,8 +207,8 @@ int BN_BLINDING_update(BN_BLINDING *b, BN_CTX *ctx)
 
        ret=1;
 err:
-       if (b->counter == 0)
-               b->counter = BN_BLINDING_COUNTER;
+       if (b->counter == BN_BLINDING_COUNTER)
+               b->counter = 0;
        return(ret);
        }
 
@@ -223,6 +229,12 @@ int BN_BLINDING_convert_ex(BIGNUM *n, BIGNUM *r, BN_BLINDING *b, BN_CTX *ctx)
                return(0);
                }
 
+       if (b->counter == -1)
+               /* Fresh blinding, doesn't need updating. */
+               b->counter = 0;
+       else if (!BN_BLINDING_update(b,ctx))
+               return(0);
+
        if (r != NULL)
                {
                if (!BN_copy(r, b->Ai)) ret=0;
@@ -243,22 +255,19 @@ int BN_BLINDING_invert_ex(BIGNUM *n, const BIGNUM *r, BN_BLINDING *b, BN_CTX *ct
        int ret;
 
        bn_check_top(n);
-       if ((b->A == NULL) || (b->Ai == NULL))
-               {
-               BNerr(BN_F_BN_BLINDING_INVERT_EX,BN_R_NOT_INITIALIZED);
-               return(0);
-               }
 
        if (r != NULL)
                ret = BN_mod_mul(n, n, r, b->mod, ctx);
        else
-               ret = BN_mod_mul(n, n, b->Ai, b->mod, ctx);
-
-       if (ret >= 0)
                {
-               if (!BN_BLINDING_update(b,ctx))
+               if (b->Ai == NULL)
+                       {
+                       BNerr(BN_F_BN_BLINDING_INVERT_EX,BN_R_NOT_INITIALIZED);
                        return(0);
+                       }
+               ret = BN_mod_mul(n, n, b->Ai, b->mod, ctx);
                }
+
        bn_check_top(n);
        return(ret);
        }

diff --git a/crypto/rsa/rsa_eay.c b/crypto/rsa/rsa_eay.c
index 412d0eacf73a5a69e8e864a566f74fff7f5f8ba3..d477f08c4cace48c50432f2563ce9a9de7735ab6 100644 (file)
--- a/crypto/rsa/rsa_eay.c
+++ b/crypto/rsa/rsa_eay.c
@@ -312,51 +312,56 @@ static BN_BLINDING *rsa_get_blinding(RSA *rsa, int *local, BN_CTX *ctx)
        return ret;
 }
 
-static int rsa_blinding_convert(BN_BLINDING *b, int local, BIGNUM *f,
-       BIGNUM *r, BN_CTX *ctx)
-{
-       if (local)
+static int rsa_blinding_convert(BN_BLINDING *b, BIGNUM *f, BIGNUM *unblind,
+       BN_CTX *ctx)
+       {
+       if (unblind == NULL)
+               /* Local blinding: store the unblinding factor
+                * in BN_BLINDING. */
                return BN_BLINDING_convert_ex(f, NULL, b, ctx);
        else
                {
-               int ret;
-               CRYPTO_r_lock(CRYPTO_LOCK_RSA_BLINDING);
-               ret = BN_BLINDING_convert_ex(f, r, b, ctx);
-               CRYPTO_r_unlock(CRYPTO_LOCK_RSA_BLINDING);
-               return ret;
-               }
-}
-
-static int rsa_blinding_invert(BN_BLINDING *b, int local, BIGNUM *f,
-       BIGNUM *r, BN_CTX *ctx)
-{
-       if (local)
-               return BN_BLINDING_invert_ex(f, NULL, b, ctx);
-       else
-               {
+               /* Shared blinding: store the unblinding factor
+                * outside BN_BLINDING. */
                int ret;
                CRYPTO_w_lock(CRYPTO_LOCK_RSA_BLINDING);
-               ret = BN_BLINDING_invert_ex(f, r, b, ctx);
+               ret = BN_BLINDING_convert_ex(f, unblind, b, ctx);
                CRYPTO_w_unlock(CRYPTO_LOCK_RSA_BLINDING);
                return ret;
                }
-}
+       }
+
+static int rsa_blinding_invert(BN_BLINDING *b, BIGNUM *f, BIGNUM *unblind,
+       BN_CTX *ctx)
+       {
+       /* For local blinding, unblind is set to NULL, and BN_BLINDING_invert_ex
+        * will use the unblinding factor stored in BN_BLINDING.
+        * If BN_BLINDING is shared between threads, unblind must be non-null:
+        * BN_BLINDING_invert_ex will then use the local unblinding factor,
+        * and will only read the modulus from BN_BLINDING.
+        * In both cases it's safe to access the blinding without a lock.
+        */
+       return BN_BLINDING_invert_ex(f, unblind, b, ctx);
+       }
 
 /* signing */
 static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
             unsigned char *to, RSA *rsa, int padding)
        {
-       BIGNUM *f, *ret, *br, *res;
+       BIGNUM *f, *ret, *res;
        int i,j,k,num=0,r= -1;
        unsigned char *buf=NULL;
        BN_CTX *ctx=NULL;
        int local_blinding = 0;
+       /* Used only if the blinding structure is shared. A non-NULL unblind
+        * instructs rsa_blinding_convert() and rsa_blinding_invert() to store
+        * the unblinding factor outside the blinding structure. */
+       BIGNUM *unblind = NULL;
        BN_BLINDING *blinding = NULL;
 
        if ((ctx=BN_CTX_new()) == NULL) goto err;
        BN_CTX_start(ctx);
        f   = BN_CTX_get(ctx);
-       br  = BN_CTX_get(ctx);
        ret = BN_CTX_get(ctx);
        num = BN_num_bytes(rsa->n);
        buf = OPENSSL_malloc(num);
@@ -404,8 +409,15 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
                }
        
        if (blinding != NULL)
-               if (!rsa_blinding_convert(blinding, local_blinding, f, br, ctx))
+               {
+               if (!local_blinding && ((unblind = BN_CTX_get(ctx)) == NULL))
+                       {
+                       RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT,ERR_R_MALLOC_FAILURE);
+                       goto err;
+                       }
+               if (!rsa_blinding_convert(blinding, f, unblind, ctx))
                        goto err;
+               }
 
        if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||
                ((rsa->p != NULL) &&
@@ -439,7 +451,7 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
                }
 
        if (blinding)
-               if (!rsa_blinding_invert(blinding, local_blinding, ret, br, ctx))
+               if (!rsa_blinding_invert(blinding, ret, unblind, ctx))
                        goto err;
 
        if (padding == RSA_X931_PADDING)
@@ -478,18 +490,21 @@ err:
 static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
             unsigned char *to, RSA *rsa, int padding)
        {
-       BIGNUM *f, *ret, *br;
+       BIGNUM *f, *ret;
        int j,num=0,r= -1;
        unsigned char *p;
        unsigned char *buf=NULL;
        BN_CTX *ctx=NULL;
        int local_blinding = 0;
+       /* Used only if the blinding structure is shared. A non-NULL unblind
+        * instructs rsa_blinding_convert() and rsa_blinding_invert() to store
+        * the unblinding factor outside the blinding structure. */
+       BIGNUM *unblind = NULL;
        BN_BLINDING *blinding = NULL;
 
        if((ctx = BN_CTX_new()) == NULL) goto err;
        BN_CTX_start(ctx);
        f   = BN_CTX_get(ctx);
-       br  = BN_CTX_get(ctx);
        ret = BN_CTX_get(ctx);
        num = BN_num_bytes(rsa->n);
        buf = OPENSSL_malloc(num);
@@ -527,8 +542,15 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
                }
        
        if (blinding != NULL)
-               if (!rsa_blinding_convert(blinding, local_blinding, f, br, ctx))
+               {
+               if (!local_blinding && ((unblind = BN_CTX_get(ctx)) == NULL))
+                       {
+                       RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT,ERR_R_MALLOC_FAILURE);
                        goto err;
+                       }
+               if (!rsa_blinding_convert(blinding, f, unblind, ctx))
+                       goto err;
+               }
 
        /* do the decrypt */
        if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||
@@ -562,7 +584,7 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
                }
 
        if (blinding)
-               if (!rsa_blinding_invert(blinding, local_blinding, ret, br, ctx))
+               if (!rsa_blinding_invert(blinding, ret, unblind, ctx))
                        goto err;
 
        p=buf;