Update hkdf.c to avoid potentially vulnerable code pattern.

Nicky Mouha · davidben · commit 47b2fefb0312 · 2023-05-18T23:05:56.000Z
Change-Id: I190fcdb0b9667b0ac6f490b36edc63237af7fffb Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/59905 Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/crypto/fipsmodule/hkdf/hkdf.c b/crypto/fipsmodule/hkdf/hkdf.c
@@ -94,7 +94,7 @@ int HKDF_expand(uint8_t *out_key, size_t out_len, const EVP_MD *digest,
     }
 
     todo = digest_len;
-    if (done + todo > out_len) {
+    if (todo > out_len - done) {
       todo = out_len - done;
     }
     OPENSSL_memcpy(out_key + done, previous, todo);

Original file line number	Diff line number	Diff line change
`@@ -94,7 +94,7 @@ int HKDF_expand(uint8_t out_key, size_t out_len, const EVP_MD digest,`
`94`	`94`	`}`
`95`	`95`
`96`	`96`	`todo = digest_len;`
`97`		`- if (done + todo > out_len) {`
	`97`	`+ if (todo > out_len - done) {`
`98`	`98`	`todo = out_len - done;`
`99`	`99`	`}`
`100`	`100`	`OPENSSL_memcpy(out_key + done, previous, todo);`