9500 HP scanner needs smaller SMB2 rwsize

@@ -48,10 +48,19 @@
 uint32_t smb2_tcp_bufsize = (1<<22);    /* 4MB */
 uint32_t smb2_max_rwsize = (1<<20);     /* 1MB */
 uint32_t smb2_max_trans  = (1<<16);     /* 64KB */
 
 /*
+ * With clients (e.g. HP scanners) that don't advertise SMB2_CAP_LARGE_MTU
+ * (including all clients using dialect < SMB 2.1), use a "conservative" value
+ * for max r/w size because some older clients misbehave with larger values.
+ * 64KB is recommended in the [MS-SMB2] spec.  (3.3.5.3.1 SMB 2.1 or SMB 3.x
+ * Support) as the minimum so we'll use that.
+ */
+uint32_t smb2_old_rwsize = (1<<16);     /* 64KB */
+
+/*
  * List of all SMB2 versions we implement.  Note that the
  * highest version we support may be limited by the
  * _cfg.skc_max_protocol setting.
  */
 static uint16_t smb2_versions[] = {

@@ -247,10 +256,11 @@
 smb2_negotiate_common(smb_request_t *sr, uint16_t version)
 {
         timestruc_t boot_tv, now_tv;
         smb_session_t *s = sr->session;
         int rc;
+        uint32_t max_rwsize;
         uint16_t secmode;
 
         sr->smb2_status = 0;
 
         /*

@@ -295,10 +305,18 @@
                 smb2sr_put_error(sr, sr->smb2_status);
                 smb2_send_reply(sr);
                 return (-1); /* will drop */
         }
 
+        /*
+         * See notes above smb2_max_rwsize, smb2_old_rwsize
+         */
+        if (s->capabilities & SMB2_CAP_LARGE_MTU)
+                max_rwsize = smb2_max_rwsize;
+        else
+                max_rwsize = smb2_old_rwsize;
+
         rc = smb_mbc_encodef(
             &sr->reply,
             "wwww#cllllTTwwl#c",
             65, /* StructSize */        /* w */
             s->secmode,                 /* w */

@@ -306,12 +324,12 @@
             0, /* reserved */           /* w */
             UUID_LEN,                   /* # */
             &s->s_cfg.skc_machine_uuid, /* c */
             smb2srv_capabilities,       /* l */
             smb2_max_trans,             /* l */
-            smb2_max_rwsize,            /* l */
-            smb2_max_rwsize,            /* l */
+            max_rwsize,                 /* l */
+            max_rwsize,                 /* l */
             &now_tv,                    /* T */
             &boot_tv,                   /* T */
             128, /* SecBufOff */        /* w */
             sr->sr_cfg->skc_negtok_len, /* w */
             0,  /* reserved */          /* l */