diff --git a/ChangeLog.d/fix-build-netbsd.txt b/ChangeLog.d/fix-build-netbsd.txt
new file mode 100644
index 0000000..000614e
--- /dev/null
+++ b/ChangeLog.d/fix-build-netbsd.txt
@@ -0,0 +1,5 @@
+Bugfix
+   * Fix building library/net_sockets.c and the ssl_mail_client program on
+     NetBSD. NetBSD conditionals were added for the backport to avoid the risk
+     of breaking a platform. Original fix contributed by Nia Alarie in #3422.
+     Adapted for long-term support branch 2.16 in #3558.
diff --git a/ChangeLog.d/netbsd-rand-arc4random_buf.txt b/ChangeLog.d/netbsd-rand-arc4random_buf.txt
new file mode 100644
index 0000000..8539d1f
--- /dev/null
+++ b/ChangeLog.d/netbsd-rand-arc4random_buf.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Use arc4random_buf on NetBSD instead of rand implementation with cyclical
+     lower bits. Fix contributed in #3540.
diff --git a/ChangeLog.d/x509write_csr_heap_alloc.txt b/ChangeLog.d/x509write_csr_heap_alloc.txt
new file mode 100644
index 0000000..6223698
--- /dev/null
+++ b/ChangeLog.d/x509write_csr_heap_alloc.txt
@@ -0,0 +1,4 @@
+Bugfix
+   * Reduce the stack consumption of mbedtls_x509write_csr_der() which
+     previously could lead to stack overflow on constrained devices.
+     Contributed by Doru Gucea and Simon Leet in #3464.
diff --git a/library/net_sockets.c b/library/net_sockets.c
index 9489576..303e5e8 100644
--- a/library/net_sockets.c
+++ b/library/net_sockets.c
@@ -51,6 +51,10 @@
  * Harmless on other platforms. */
 #define _POSIX_C_SOURCE 200112L
 
+#if defined(__NetBSD__)
+#define _XOPEN_SOURCE 600 /* sockaddr_storage */
+#endif
+
 #if !defined(MBEDTLS_CONFIG_FILE)
 #include "mbedtls/config.h"
 #else
@@ -345,8 +349,9 @@
 
     struct sockaddr_storage client_addr;
 
-#if defined(__socklen_t_defined) || defined(_SOCKLEN_T) ||  \
-    defined(_SOCKLEN_T_DECLARED) || defined(__DEFINED_socklen_t)
+#if defined(__socklen_t_defined) || defined(_SOCKLEN_T) || \
+    defined(_SOCKLEN_T_DECLARED) || defined(__DEFINED_socklen_t) || \
+    ( defined(__NetBSD__) && defined(socklen_t) )
     socklen_t n = (socklen_t) sizeof( client_addr );
     socklen_t type_len = (socklen_t) sizeof( type );
 #else
diff --git a/library/rsa.c b/library/rsa.c
index af1cef6..f3b1918 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -83,7 +83,7 @@
 #include "mbedtls/md.h"
 #endif
 
-#if defined(MBEDTLS_PKCS1_V15) && !defined(__OpenBSD__)
+#if defined(MBEDTLS_PKCS1_V15) && !defined(__OpenBSD__) && !defined(__NetBSD__)
 #include <stdlib.h>
 #endif
 
@@ -2590,7 +2590,7 @@
 #if defined(MBEDTLS_PKCS1_V15)
 static int myrand( void *rng_state, unsigned char *output, size_t len )
 {
-#if !defined(__OpenBSD__)
+#if !defined(__OpenBSD__) && !defined(__NetBSD__)
     size_t i;
 
     if( rng_state != NULL )
@@ -2603,7 +2603,7 @@
         rng_state = NULL;
 
     arc4random_buf( output, len );
-#endif /* !OpenBSD */
+#endif /* !OpenBSD && !NetBSD */
 
     return( 0 );
 }
diff --git a/library/x509write_csr.c b/library/x509write_csr.c
index d1b0716..ac5eaaa 100644
--- a/library/x509write_csr.c
+++ b/library/x509write_csr.c
@@ -81,6 +81,14 @@
 #define SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
 #endif
 
+#if defined(MBEDTLS_PLATFORM_C)
+#include "mbedtls/platform.h"
+#else
+#include <stdlib.h>
+#define mbedtls_calloc    calloc
+#define mbedtls_free      free
+#endif
+
 void mbedtls_x509write_csr_init( mbedtls_x509write_csr *ctx )
 {
     memset( ctx, 0, sizeof( mbedtls_x509write_csr ) );
@@ -187,71 +195,85 @@
     return( 0 );
 }
 
-int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf, size_t size,
-                       int (*f_rng)(void *, unsigned char *, size_t),
-                       void *p_rng )
+static int x509write_csr_der_internal( mbedtls_x509write_csr *ctx,
+                                 unsigned char *buf,
+                                 size_t size,
+                                 unsigned char *sig,
+                                 int (*f_rng)(void *, unsigned char *, size_t),
+                                 void *p_rng )
 {
     int ret;
     const char *sig_oid;
     size_t sig_oid_len = 0;
     unsigned char *c, *c2;
     unsigned char hash[64];
-    unsigned char sig[SIGNATURE_MAX_SIZE];
-    unsigned char tmp_buf[2048];
     size_t pub_len = 0, sig_and_oid_len = 0, sig_len;
     size_t len = 0;
     mbedtls_pk_type_t pk_alg;
 
-    /*
-     * Prepare data to be signed in tmp_buf
-     */
-    c = tmp_buf + sizeof( tmp_buf );
+    /* Write the CSR backwards starting from the end of buf */
+    c = buf + size;
 
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, tmp_buf, ctx->extensions ) );
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_extensions( &c, buf,
+                                                           ctx->extensions ) );
 
     if( len )
     {
-        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
-        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
-                                                        MBEDTLS_ASN1_SEQUENCE ) );
+        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
+        MBEDTLS_ASN1_CHK_ADD( len,
+            mbedtls_asn1_write_tag(
+                &c, buf,
+                MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
 
-        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
-        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
-                                                        MBEDTLS_ASN1_SET ) );
+        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
+        MBEDTLS_ASN1_CHK_ADD( len,
+            mbedtls_asn1_write_tag(
+                &c, buf,
+                MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET ) );
 
-        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( &c, tmp_buf, MBEDTLS_OID_PKCS9_CSR_EXT_REQ,
-                                          MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_CSR_EXT_REQ ) ) );
+        MBEDTLS_ASN1_CHK_ADD( len,
+            mbedtls_asn1_write_oid(
+                &c, buf, MBEDTLS_OID_PKCS9_CSR_EXT_REQ,
+                MBEDTLS_OID_SIZE( MBEDTLS_OID_PKCS9_CSR_EXT_REQ ) ) );
 
-        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
-        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
-                                                        MBEDTLS_ASN1_SEQUENCE ) );
+        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
+        MBEDTLS_ASN1_CHK_ADD( len,
+            mbedtls_asn1_write_tag(
+                &c, buf,
+                MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
     }
 
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
-                                                    MBEDTLS_ASN1_CONTEXT_SPECIFIC ) );
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
+    MBEDTLS_ASN1_CHK_ADD( len,
+        mbedtls_asn1_write_tag(
+            &c, buf,
+            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CONTEXT_SPECIFIC ) );
 
     MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_pk_write_pubkey_der( ctx->key,
-                                                tmp_buf, c - tmp_buf ) );
+                                                              buf, c - buf ) );
     c -= pub_len;
     len += pub_len;
 
     /*
      *  Subject  ::=  Name
      */
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, tmp_buf, ctx->subject ) );
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_x509_write_names( &c, buf,
+                                                         ctx->subject ) );
 
     /*
      *  Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
      */
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, tmp_buf, 0 ) );
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 0 ) );
 
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, tmp_buf, len ) );
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, tmp_buf, MBEDTLS_ASN1_CONSTRUCTED |
-                                                    MBEDTLS_ASN1_SEQUENCE ) );
+    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
+    MBEDTLS_ASN1_CHK_ADD( len,
+        mbedtls_asn1_write_tag(
+            &c, buf,
+            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
 
     /*
-     * Prepare signature
+     * Sign the written CSR data into the sig buffer
+     * Note: hash errors can happen only after an internal error
      */
     ret = mbedtls_md( mbedtls_md_info_from_type( ctx->md_alg ), c, len, hash );
     if( ret != 0 )
@@ -271,32 +293,68 @@
         return( MBEDTLS_ERR_X509_INVALID_ALG );
 
     if( ( ret = mbedtls_oid_get_oid_by_sig_alg( pk_alg, ctx->md_alg,
-                                                &sig_oid, &sig_oid_len ) ) != 0 )
+                                              &sig_oid, &sig_oid_len ) ) != 0 )
     {
         return( ret );
     }
 
     /*
-     * Write data to output buffer
+     * Move the written CSR data to the start of buf to create space for
+     * writing the signature into buf.
+     */
+    memmove( buf, c, len );
+
+    /*
+     * Write sig and its OID into buf backwards from the end of buf.
+     * Note: mbedtls_x509_write_sig will check for c2 - ( buf + len ) < sig_len
+     * and return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL if needed.
      */
     c2 = buf + size;
-    MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len, mbedtls_x509_write_sig( &c2, buf,
-                                        sig_oid, sig_oid_len, sig, sig_len ) );
+    MBEDTLS_ASN1_CHK_ADD( sig_and_oid_len,
+        mbedtls_x509_write_sig( &c2, buf + len, sig_oid, sig_oid_len,
+                                sig, sig_len ) );
 
-    if( len > (size_t)( c2 - buf ) )
-        return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
-
+    /*
+     * Compact the space between the CSR data and signature by moving the
+     * CSR data to the start of the signature.
+     */
     c2 -= len;
-    memcpy( c2, c, len );
+    memmove( c2, buf, len );
 
+    /* ASN encode the total size and tag the CSR data with it. */
     len += sig_and_oid_len;
     MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c2, buf, len ) );
-    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c2, buf, MBEDTLS_ASN1_CONSTRUCTED |
-                                                 MBEDTLS_ASN1_SEQUENCE ) );
+    MBEDTLS_ASN1_CHK_ADD( len,
+        mbedtls_asn1_write_tag(
+            &c2, buf,
+            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
+
+    /* Zero the unused bytes at the start of buf */
+    memset( buf, 0, c2 - buf);
 
     return( (int) len );
 }
 
+int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf,
+                               size_t size,
+                               int (*f_rng)(void *, unsigned char *, size_t),
+                               void *p_rng )
+{
+    int ret;
+    unsigned char *sig;
+
+    if( ( sig = mbedtls_calloc( 1, SIGNATURE_MAX_SIZE ) ) == NULL )
+    {
+        return( MBEDTLS_ERR_X509_ALLOC_FAILED );
+    }
+
+    ret = x509write_csr_der_internal( ctx, buf, size, sig, f_rng, p_rng );
+
+    mbedtls_free( sig );
+
+    return( ret );
+}
+
 #define PEM_BEGIN_CSR           "-----BEGIN CERTIFICATE REQUEST-----\n"
 #define PEM_END_CSR             "-----END CERTIFICATE REQUEST-----\n"
 
diff --git a/programs/ssl/ssl_mail_client.c b/programs/ssl/ssl_mail_client.c
index 97d5d8a..b519491 100644
--- a/programs/ssl/ssl_mail_client.c
+++ b/programs/ssl/ssl_mail_client.c
@@ -51,6 +51,10 @@
  * Harmless on other platforms. */
 #define _POSIX_C_SOURCE 200112L
 
+#if defined(__NetBSD__)
+#define _XOPEN_SOURCE 600
+#endif
+
 #if !defined(MBEDTLS_CONFIG_FILE)
 #include "mbedtls/config.h"
 #else
diff --git a/tests/compat.sh b/tests/compat.sh
index 3626642..1244560 100755
--- a/tests/compat.sh
+++ b/tests/compat.sh
@@ -1259,7 +1259,7 @@
             cp $CLI_OUT c-cli-${TESTS}.log
             echo "  ! outputs saved to c-srv-${TESTS}.log, c-cli-${TESTS}.log"
 
-            if [ "X${USER:-}" = Xbuildbot -o "X${LOGNAME:-}" = Xbuildbot -o "${LOG_FAILURE_ON_STDOUT:-0}" != 0 ]; then
+            if [ "${LOG_FAILURE_ON_STDOUT:-0}" != 0 ]; then
                 echo "  ! server output:"
                 cat c-srv-${TESTS}.log
                 echo "  ! ==================================================="
diff --git a/tests/git-scripts/pre-commit.sh b/tests/git-scripts/pre-commit.sh
new file mode 100755
index 0000000..4365686
--- /dev/null
+++ b/tests/git-scripts/pre-commit.sh
@@ -0,0 +1,36 @@
+#!/bin/sh
+
+# pre-commit.sh
+#
+# Copyright (c) 2017, ARM Limited, All Rights Reserved
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# This file is part of Mbed TLS (https://tls.mbed.org)
+
+# Purpose
+#
+# This script does quick sanity checks before commiting:
+#   - check that generated files are up-to-date.
+#
+# It is meant to be called as a git pre-commit hook, see README.md.
+#
+# From the git sample pre-commit hook:
+#   Called by "git commit" with no arguments.  The hook should
+#   exit with non-zero status after issuing an appropriate message if
+#   it wants to stop the commit.
+
+set -eu
+
+tests/scripts/check-generated-files.sh
diff --git a/tests/scripts/check-generated-files.sh b/tests/scripts/check-generated-files.sh
index 516437e..5776daa 100755
--- a/tests/scripts/check-generated-files.sh
+++ b/tests/scripts/check-generated-files.sh
@@ -50,11 +50,29 @@
 
 set -eu
 
+if [ $# -ne 0 ] && [ "$1" = "--help" ]; then
+    cat <<EOF
+$0 [-u]
+This script checks that all generated file are up-to-date. If some aren't, by
+default the scripts reports it and exits in error; with the -u option, it just
+updates them instead.
+
+  -u    Update the files rather than return an error for out-of-date files.
+EOF
+    exit
+fi
+
 if [ -d library -a -d include -a -d tests ]; then :; else
     echo "Must be run from mbed TLS root" >&2
     exit 1
 fi
 
+UPDATE=
+if [ $# -ne 0 ] && [ "$1" = "-u" ]; then
+    shift
+    UPDATE='y'
+fi
+
 check()
 {
     SCRIPT=$1
@@ -80,9 +98,15 @@
     for FILE in $FILES; do
         if ! diff $FILE $FILE.bak >/dev/null 2>&1; then
             echo "'$FILE' was either modified or deleted by '$SCRIPT'"
-            exit 1
+            if [ -z "$UPDATE" ]; then
+                exit 1
+            fi
         fi
-        mv $FILE.bak $FILE
+        if [ -z "$UPDATE" ]; then
+            mv $FILE.bak $FILE
+        else
+            rm $FILE.bak
+        fi
 
         if [ -d $TO_CHECK ]; then
             # Create a grep regular expression that we can check against the
@@ -99,7 +123,9 @@
         # Check if there are any new files
         if ls -1 $TO_CHECK | grep -v "$PATTERN" >/dev/null 2>&1; then
             echo "Files were created by '$SCRIPT'"
-            exit 1
+            if [ -z "$UPDATE" ]; then
+                exit 1
+            fi
         fi
     fi
 }
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 9d4f650..8398ab8 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -405,7 +405,7 @@
     fi
     echo "  ! outputs saved to o-XXX-${TESTS}.log"
 
-    if [ "X${USER:-}" = Xbuildbot -o "X${LOGNAME:-}" = Xbuildbot -o "${LOG_FAILURE_ON_STDOUT:-0}" != 0 ]; then
+    if [ "${LOG_FAILURE_ON_STDOUT:-0}" != 0 ]; then
         echo "  ! server output:"
         cat o-srv-${TESTS}.log
         echo "  ! ========================================================"
@@ -621,6 +621,19 @@
         return
     fi
 
+    # update DTLS variable
+    detect_dtls "$SRV_CMD"
+
+    # if the test uses DTLS but no custom proxy, add a simple proxy
+    # as it provides timing info that's useful to debug failures
+    if [ -z "$PXY_CMD" ] && [ "$DTLS" -eq 1 ]; then
+        PXY_CMD="$P_PXY"
+        case " $SRV_CMD " in
+            *' server_addr=::1 '*)
+                PXY_CMD="$PXY_CMD server_addr=::1 listen_addr=::1";;
+        esac
+    fi
+
     # fix client port
     if [ -n "$PXY_CMD" ]; then
         CLI_CMD=$( echo "$CLI_CMD" | sed s/+SRV_PORT/$PXY_PORT/g )
@@ -628,9 +641,6 @@
         CLI_CMD=$( echo "$CLI_CMD" | sed s/+SRV_PORT/$SRV_PORT/g )
     fi
 
-    # update DTLS variable
-    detect_dtls "$SRV_CMD"
-
     # prepend valgrind to our commands if active
     if [ "$MEMCHECK" -gt 0 ]; then
         if is_polar "$SRV_CMD"; then
@@ -647,19 +657,19 @@
 
         # run the commands
         if [ -n "$PXY_CMD" ]; then
-            echo "$PXY_CMD" > $PXY_OUT
+            printf "# %s\n%s\n" "$NAME" "$PXY_CMD" > $PXY_OUT
             $PXY_CMD >> $PXY_OUT 2>&1 &
             PXY_PID=$!
             wait_proxy_start "$PXY_PORT" "$PXY_PID"
         fi
 
         check_osrv_dtls
-        echo "$SRV_CMD" > $SRV_OUT
+        printf "# $NAME\n$SRV_CMD\n" > $SRV_OUT
         provide_input | $SRV_CMD >> $SRV_OUT 2>&1 &
         SRV_PID=$!
         wait_server_start "$SRV_PORT" "$SRV_PID"
 
-        echo "$CLI_CMD" > $CLI_OUT
+        printf "# $NAME\n$CLI_CMD\n" > $CLI_OUT
         eval "$CLI_CMD" >> $CLI_OUT 2>&1 &
         wait_client_done
 
diff --git a/tests/suites/helpers.function b/tests/suites/helpers.function
index cd9346e..523db86 100644
--- a/tests/suites/helpers.function
+++ b/tests/suites/helpers.function
@@ -549,7 +549,7 @@
  */
 static int rnd_std_rand( void *rng_state, unsigned char *output, size_t len )
 {
-#if !defined(__OpenBSD__)
+#if !defined(__OpenBSD__) && !defined(__NetBSD__)
     size_t i;
 
     if( rng_state != NULL )
@@ -562,7 +562,7 @@
         rng_state = NULL;
 
     arc4random_buf( output, len );
-#endif /* !OpenBSD */
+#endif /* !OpenBSD && !NetBSD */
 
     return( 0 );
 }