Improve error checking of some |BN_CTX_get| callers. The documentation for |BN_CTX_get| states: "Once |BN_CTX_get| has returned NULL, all future calls will also return NULL until |BN_CTX_end| is called." Some code takes advantage of that guarantee by only checking the return value of the last call to |BN_CTX_get| in a series of calls. That is correct and the most efficient way of doing it. However, that pattern is inconsistent with most of the other uses of |BN_CTX_get|. Also, static analysis tools like Coverity cannot understand that pattern. This commit removes the instances of that pattern that Coverity complained about when scanning *ring*. Change-Id: Ie36d0223ea1caee460c7979547cf5bfd5fb16f93 Reviewed-on: https://boringssl-review.googlesource.com/5611 Reviewed-by: Adam Langley <agl@google.com>

diff --git a/crypto/ec/oct.c b/crypto/ec/oct.c
index b0519b6..cb50e17 100644
--- a/crypto/ec/oct.c
+++ b/crypto/ec/oct.c

@@ -231,7 +231,7 @@
   BN_CTX_start(ctx);
   x = BN_CTX_get(ctx);
   y = BN_CTX_get(ctx);
-  if (y == NULL) {
+  if (x == NULL || y == NULL) {
     goto err;
   }
 

diff --git a/crypto/ec/simple.c b/crypto/ec/simple.c
index 3659dba..c62199c 100644
--- a/crypto/ec/simple.c
+++ b/crypto/ec/simple.c

@@ -524,7 +524,7 @@
   Z_1 = BN_CTX_get(ctx);
   Z_2 = BN_CTX_get(ctx);
   Z_3 = BN_CTX_get(ctx);
-  if (Z_3 == NULL) {
+  if (Z == NULL || Z_1 == NULL || Z_2 == NULL || Z_3 == NULL) {
     goto err;
   }
 

diff --git a/crypto/ecdsa/ecdsa.c b/crypto/ecdsa/ecdsa.c
index 1d1fc36..8403d60 100644
--- a/crypto/ecdsa/ecdsa.c
+++ b/crypto/ecdsa/ecdsa.c

@@ -172,7 +172,7 @@
   u2 = BN_CTX_get(ctx);
   m = BN_CTX_get(ctx);
   X = BN_CTX_get(ctx);
-  if (!X) {
+  if (order == NULL || u1 == NULL || u2 == NULL || m == NULL || X == NULL) {
     OPENSSL_PUT_ERROR(ECDSA, ERR_R_BN_LIB);
     goto err;
   }

diff --git a/crypto/rsa/rsa_impl.c b/crypto/rsa/rsa_impl.c
index d24f152..e1dcaf3 100644
--- a/crypto/rsa/rsa_impl.c
+++ b/crypto/rsa/rsa_impl.c

@@ -840,7 +840,7 @@
   r1 = BN_CTX_get(ctx);
   r2 = BN_CTX_get(ctx);
   r3 = BN_CTX_get(ctx);
-  if (r3 == NULL) {
+  if (r0 == NULL || r1 == NULL || r2 == NULL || r3 == NULL) {
     goto err;
   }