From 3360eeb74b660b9a5911d624b7d363151a7609b5 Mon Sep 17 00:00:00 2001
From: Eric Blankenhorn <eric@wolfssl.com>
Date: Wed, 24 Jun 2026 13:56:02 -0500
Subject: [PATCH] Fix wolfSSL_BUF_MEM_grow_ex with WOLFSSL_NO_REALLOC

---
 .github/workflows/smoke-test.yml |  3 +++
 src/ssl.c                        |  4 +++-
 tests/api.c                      | 23 +++++++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/smoke-test.yml b/.github/workflows/smoke-test.yml
index 5cb6f198b3b..e849389f36e 100644
--- a/.github/workflows/smoke-test.yml
+++ b/.github/workflows/smoke-test.yml
@@ -150,6 +150,9 @@ jobs:
             {"name": "sanitize-asan", "configure": ["--enable-all"],
              "cflags": "-fsanitize=address -fno-omit-frame-pointer -g -O1",
              "ldflags": "-fsanitize=address"},
+            {"name": "opensslextra-norealloc-asan", "configure": ["--enable-opensslextra"],
+             "cflags": "-DWOLFSSL_NO_REALLOC -fsanitize=address -fno-omit-frame-pointer -g -O1",
+             "ldflags": "-fsanitize=address"},
             {"name": "enable-all-smallstack", "configure": ["--enable-all", "--enable-smallstack"]},
             {"name": "enable-all", "configure": ["--enable-all"]},
             {"name": "integration", "configure": ["--enable-openssh", "--enable-lighty", "--enable-stunnel", "--enable-opensslextra"]},
diff --git a/src/ssl.c b/src/ssl.c
index c2a5827c9dd..c546296cc75 100644
--- a/src/ssl.c
+++ b/src/ssl.c
@@ -15429,7 +15429,9 @@ int wolfSSL_BUF_MEM_grow_ex(WOLFSSL_BUF_MEM* buf, size_t len,
 #ifdef WOLFSSL_NO_REALLOC
     tmp = (char*)XMALLOC(mx, NULL, DYNAMIC_TYPE_OPENSSL);
     if (tmp != NULL && buf->data != NULL) {
-       XMEMCPY(tmp, buf->data, len_int);
+       /* only the existing content is valid in the old buffer; copying
+        * len_int (the new, larger size) would read past buf->max */
+       XMEMCPY(tmp, buf->data, buf->length);
        XFREE(buf->data, NULL, DYNAMIC_TYPE_OPENSSL);
        buf->data = NULL;
     }
diff --git a/tests/api.c b/tests/api.c
index 32b90b9a079..59c7ee48980 100644
--- a/tests/api.c
+++ b/tests/api.c
@@ -17034,10 +17034,33 @@ static int test_wolfSSL_BUF(void)
     EXPECT_DECLS;
 #if defined(OPENSSL_EXTRA)
     BUF_MEM* buf = NULL;
+    unsigned char pattern[16];
+
     ExpectNotNull(buf = BUF_MEM_new());
     ExpectIntEQ(BUF_MEM_grow(buf, 10), 10);
     ExpectIntEQ(BUF_MEM_grow(buf, -1), 0);
     BUF_MEM_free(buf);
+    buf = NULL;
+
+    /* Regression test for a heap over-read in wolfSSL_BUF_MEM_grow_ex(): the
+     * WOLFSSL_NO_REALLOC path copied the new (larger) size from the old buffer,
+     * reading (len - buf->max) bytes past it. Those stray bytes are then zeroed
+     * by the grow, so the over-read is observable only under a memory sanitizer
+     * (ASAN/valgrind) built with WOLFSSL_NO_REALLOC. The content check below is
+     * a sanity check that passes on both the buggy and fixed paths. */
+    XMEMSET(pattern, 0x55, sizeof(pattern));
+    ExpectNotNull(buf = BUF_MEM_new());
+    /* establish a small allocation, then seed it with a known pattern */
+    ExpectIntEQ(BUF_MEM_grow(buf, sizeof(pattern)), (int)sizeof(pattern));
+    if (buf != NULL && buf->data != NULL)
+        XMEMCPY(buf->data, pattern, sizeof(pattern));
+    /* grow well past buf->max to exercise the malloc+copy+free path */
+    ExpectIntEQ(BUF_MEM_grow(buf, 256), 256);
+    ExpectNotNull(buf == NULL ? NULL : buf->data);
+    /* sanity check; the over-read itself is flagged by ASAN, not this assert */
+    if (buf != NULL && buf->data != NULL)
+        ExpectIntEQ(XMEMCMP(buf->data, pattern, sizeof(pattern)), 0);
+    BUF_MEM_free(buf);
 #endif
     return EXPECT_RESULT();
 }