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NEX-20371 SMB2 message sizes cause lock contention in page_create_va
Reviewed by: Rick McNeal <rick.mcneal@nexenta.com>
Reviewed by: Roman Strashkin <roman.strashkin@nexenta.com>
Reviewed by: Matt Barden <matt.barden@nexenta.com>
NEX-19944 SMB2 server should require signed Validate Negotiate requests
Reviewed by: Gordon Ross <gordon.ross@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
NEX-17589 Get "too high" smbd error when copy big file to cifs share (redo)
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
NEX-17289 Minimal SMB 3.0.2 support
Reviewed by: Gordon Ross <gordon.ross@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
NEX-17001 illumos 9500 HP scanner needs smaller SMB2 rwsize
9500 HP scanner needs smaller SMB2 rwsize
Reviewed by: Yuri Pankov <yuripv@yuripv.net>
Reviewed by: Andy Fiddaman <omnios@citrus-it.net>
Reviewed by: Bill Sommerfeld <sommerfeld@hamachi.org>
Reviewed by: Toomas Soome <tsoome@me.com>
Approved by: Gordon Ross <gordon.w.ross@gmail.com>
NEX-15959 SMB 2.1 negotiation failure after NEX-9808
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
NEX-15959 SMB 2.1 negotiation failure after NEX-9808
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
NEX-9808 SMB3 persistent handles
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
NEX-15578 SMB2 durable handle redesign
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
NEX-5665 SMB2 oplock leases
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
Reviewed by: Roman Strashkin <roman.strashkin@nexenta.com>
NEX-9808 SMB3 persistent handles
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
NEX-15578 SMB2 durable handle redesign
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
NEX-5665 SMB2 oplock leases
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
Reviewed by: Roman Strashkin <roman.strashkin@nexenta.com>
NEX-10231 SMB logon fails in fksmbd (small fix)
NEX-10019 SMB server min_protocol setting
Reviewed by: Gordon Ross <gordon.ross@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
NEX-10231 SMB logon fails in fksmbd
Reviewed by: Evan Layton <evan.layton@nexenta.com>
Reviewed by: Gordon Ross <gordon.ross@nexenta.com>
NEX-1643 dtrace provider for smbsrv
Reviewed by: Evan Layton <evan.layton@nexenta.com>
Reviewed by: Matt Barden <matt.barden@nexenta.com>
NEX-9864 Some SMB cancel races remain after NEX-5845
Revert (part of) "NEX-5845 rework SMB immediate cancel"
reverts (part of) commit 7a5da69f6d42b17ebcc95ca3d02925d07a01343e.
Reviewed by: Matt Barden <matt.barden@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
NEX-5273 SMB 3 Encryption
Reviewed by: Gordon Ross <gordon.ross@nexenta.com>
Reviewed by: Evan Layton <evan.layton@nexenta.com>
Reviewed by: Roman Strashkin <roman.strashkin@nexenta.com>
NEX-5844 want SMB2 ioctl FSCTL_SRV_COPYCHUNK
NEX-6124 smb_fsop_read/write should allow file != sr->fid_ofile
NEX-6125 smbtorture invalid response with smb2.ioctl
Reviewed by: Evan Layton <evan.layton@nexenta.com>
Reviewed by: Matt Barden <matt.barden@nexenta.com>
NEX-4598 SMB2 credit shortage with Mac client
Reviewed by: Bayard Bell <bayard.bell@nexenta.com>
Reviewed by: Kevin Crowe <kevin.crowe@nexenta.com>
Reviewed by: Matt Barden <Matt.Barden@nexenta.com>
NEX-3738 Should support SMB2_CAP_LARGE_MTU
Reviewed by: Alek Pinchuk <alek@nexenta.com>
Reviewed by: Bayard Bell <bayard.bell@nexenta.com>
Reviewed by: Kevin Crowe <kevin.crowe@nexenta.com>
Reviewed by: Matt Barden <Matt.Barden@nexenta.com>
NEX-3610 CLONE NEX-3591 SMB3 signing
Reviewed by: Gordon Ross <gwr@nexenta.com>
Reviewed by: Dan Fields <dan.fields@nexenta.com>
NEX-3611 CLONE NEX-3550 Replace smb2_enable with max_protocol
Reviewed by: Yuri Pankov <Yuri.Pankov@nexenta.com>
NEX-2976 SMB2 client may fail to connect when server requires signing
Reviewed by: Bayard Bell <bayard.bell@nexenta.com>
Reviewed by: Kevin Crowe <kevin.crowe@nexenta.com>
NEX-2781 SMB2 credit handling needs work
NEX-2353 Codenomicon: SMB2 TC # 448950 - PANIC in SMB2.Compounded-commands...
SUP-887 Mac client hangs when accessing an SMB2 share on a nexenta 4.0 system
SMB-137 assertion failed: (sr->reply.chain_offset & 7) == 0, file: ../../common/fs/smbsrv/smb2_dispatch.c, line: 727
SMB-55 SMB2 signing
NEX-1059 Shared folder is not available in Windows 7/8/2012 when SMB2 is enabled in Workgroup mode
(Implement "Secure Negotiation")
NEX-1050 enable_smb2 should be smb2_enable
SMB-11 SMB2 message parse & dispatch
SMB-12 SMB2 Negotiate Protocol
SMB-13 SMB2 Session Setup
SMB-14 SMB2 Logoff
SMB-15 SMB2 Tree Connect
SMB-16 SMB2 Tree Disconnect
SMB-17 SMB2 Create
SMB-18 SMB2 Close
SMB-19 SMB2 Flush
SMB-20 SMB2 Read
SMB-21 SMB2 Write
SMB-22 SMB2 Lock/Unlock
SMB-23 SMB2 Ioctl
SMB-24 SMB2 Cancel
SMB-25 SMB2 Echo
SMB-26 SMB2 Query Dir
SMB-27 SMB2 Change Notify
SMB-28 SMB2 Query Info
SMB-29 SMB2 Set Info
SMB-30 SMB2 Oplocks
SMB-53 SMB2 Create Context options
(SMB2 code review cleanup 1, 2, 3)

@@ -8,11 +8,11 @@
  * source.  A copy of the CDDL is also available via the Internet at
  * http://www.illumos.org/license/CDDL.
  */
 
 /*
- * Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
+ * Copyright 2019 Nexenta Systems, Inc.  All rights reserved.
  */
 
 /*
  * Dispatch function for SMB2_NEGOTIATE
  */

@@ -22,12 +22,18 @@
 
 static int smb2_negotiate_common(smb_request_t *, uint16_t);
 
 uint32_t smb2srv_capabilities =
         SMB2_CAP_DFS |
-        SMB2_CAP_LARGE_MTU;
+        SMB2_CAP_LEASING |
+        SMB2_CAP_LARGE_MTU |
+        SMB2_CAP_PERSISTENT_HANDLES |
+        SMB2_CAP_ENCRYPTION;
 
+/* These are the only capabilities defined for SMB2.X */
+#define SMB_2X_CAPS (SMB2_CAP_DFS | SMB2_CAP_LEASING | SMB2_CAP_LARGE_MTU)
+
 /*
  * These are not intended as customer tunables, but dev. & test folks
  * might want to adjust them (with caution).
  *
  * smb2_tcp_bufsize is the TCP buffer size, applied to the network socket

@@ -37,38 +43,51 @@
  * multiple requests/responses.  This size should be large enough for
  * at least a few SMB2 requests, and at least 2X smb2_max_rwsize.
  *
  * smb2_max_rwsize is what we put in the SMB2 negotiate response to tell
  * the client the largest read and write request size we'll support.
- * One megabyte is a compromise between efficiency on fast networks
- * and memory consumption (for the buffers) on the server side.
+ * For now, we're using contiguous allocations, so keep this at 64KB
+ * so that (even with message overhead) allocations stay below 128KB,
+ * avoiding kmem_alloc -> page_create_va thrashing.
  *
  * smb2_max_trans is the largest "transact" send or receive, which is
  * used for directory listings and info set/get operations.
  */
 uint32_t smb2_tcp_bufsize = (1<<22);    /* 4MB */
-uint32_t smb2_max_rwsize = (1<<20);     /* 1MB */
+uint32_t smb2_max_rwsize = (1<<16);     /* 64KB */
 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.
+ * versions we support may be limited by the
+ * _cfg.skc_max_protocol and min_protocol settings.
  */
 static uint16_t smb2_versions[] = {
         0x202,  /* SMB 2.002 */
         0x210,  /* SMB 2.1 */
+        0x300,  /* SMB 3.0 */
+        0x302,  /* SMB 3.02 */
 };
 static uint16_t smb2_nversions =
     sizeof (smb2_versions) / sizeof (smb2_versions[0]);
 
 static boolean_t
 smb2_supported_version(smb_session_t *s, uint16_t version)
 {
         int i;
 
-        if (version > s->s_cfg.skc_max_protocol)
+        if (version > s->s_cfg.skc_max_protocol ||
+            version < s->s_cfg.skc_min_protocol)
                 return (B_FALSE);
         for (i = 0; i < smb2_nversions; i++)
                 if (version == smb2_versions[i])
                         return (B_TRUE);
         return (B_FALSE);

@@ -91,11 +110,10 @@
 smb1_negotiate_smb2(smb_request_t *sr)
 {
         smb_session_t *s = sr->session;
         smb_arg_negotiate_t *negprot = sr->sr_negprot;
         uint16_t smb2_version;
-        uint16_t secmode2;
         int rc;
 
         /*
          * Note: In the SMB1 negotiate command handler, we
          * agreed with one of the SMB2 dialects.  If that

@@ -105,42 +123,40 @@
          * the "wildcard" version 0x2FF, and the client will
          * come back with an SMB2 negotiate.
          */
         switch (negprot->ni_dialect) {
         case DIALECT_SMB2002:   /* SMB 2.002 (a.k.a. SMB2.0) */
-                smb2_version = 0x202;
+                smb2_version = SMB_VERS_2_002;
                 s->dialect = smb2_version;
                 s->s_state = SMB_SESSION_STATE_NEGOTIATED;
                 /* Allow normal SMB2 requests now. */
                 s->newrq_func = smb2sr_newrq;
-
-                /*
-                 * Translate SMB1 sec. mode to SMB2.
-                 */
-                secmode2 = 0;
-                if (s->secmode & NEGOTIATE_SECURITY_SIGNATURES_ENABLED)
-                        secmode2 |= SMB2_NEGOTIATE_SIGNING_ENABLED;
-                if (s->secmode & NEGOTIATE_SECURITY_SIGNATURES_REQUIRED)
-                        secmode2 |= SMB2_NEGOTIATE_SIGNING_REQUIRED;
-                s->secmode = secmode2;
                 break;
         case DIALECT_SMB2XXX:   /* SMB 2.??? (wildcard vers) */
                 /*
                  * Expecting an SMB2 negotiate next, so keep the
-                 * initial s->newrq_func.  Note that secmode is
-                 * fiction good enough to pass the signing check
-                 * in smb2_negotiate_common().  We'll check the
-                 * real secmode when the 2nd negotiate comes.
+                 * initial s->newrq_func.
                  */
                 smb2_version = 0x2FF;
-                s->secmode = SMB2_NEGOTIATE_SIGNING_ENABLED;
                 break;
         default:
                 return (SDRC_DROP_VC);
         }
 
         /*
+         * Clients that negotiate SMB2 from SMB1 have not yet had the
+         * opportunity to provide us with a secmode. However, any
+         * client that negotiates SMB2 should support signing, so
+         * this should be fiction good enough to pass the signing
+         * check in smb2_negotiate_common(). Even if the client
+         * doesn't support signing and we require it, we'll fail them
+         * later when they fail to sign the packet. For 2.???,
+         * we'll check the real secmode when the 2nd negotiate comes.
+         */
+        s->cli_secmode = SMB2_NEGOTIATE_SIGNING_ENABLED;
+
+        /*
          * We did not decode an SMB2 header, so make sure
          * the SMB2 header fields are initialized.
          * (Most are zero from smb_request_alloc.)
          * Also, the SMB1 common dispatch code reserved space
          * for an SMB1 header, which we need to undo here.

@@ -147,16 +163,36 @@
          */
         sr->smb2_reply_hdr = sr->reply.chain_offset = 0;
         sr->smb2_cmd_code = SMB2_NEGOTIATE;
 
         rc = smb2_negotiate_common(sr, smb2_version);
+        smb2_send_reply(sr);
         if (rc != 0)
                 return (SDRC_DROP_VC);
 
+        /*
+         * We sent the reply, so tell the SMB1 dispatch
+         * it should NOT (also) send a reply.
+         */
         return (SDRC_NO_REPLY);
 }
 
+static uint16_t
+smb2_find_best_dialect(smb_session_t *s, uint16_t cl_versions[],
+    uint16_t version_cnt)
+{
+        uint16_t best_version = 0;
+        int i;
+
+        for (i = 0; i < version_cnt; i++)
+                if (smb2_supported_version(s, cl_versions[i]) &&
+                    best_version < cl_versions[i])
+                        best_version = cl_versions[i];
+
+        return (best_version);
+}
+
 /*
  * SMB2 Negotiate gets special handling.  This is called directly by
  * the reader thread (see smbsr_newrq_initial) with what _should_ be
  * an SMB2 Negotiate.  Only the "\feSMB" header has been checked
  * when this is called, so this needs to check the SMB command,

@@ -166,16 +202,19 @@
  * know this is the only thread currently using this session.
  * This has to duplicate some of what smb2sr_work does as a
  * result of bypassing the normal dispatch mechanism.
  *
  * The caller always frees this request.
+ *
+ * Return value is 0 for success, and anything else will
+ * terminate the reader thread (drop the connection).
  */
 int
 smb2_newrq_negotiate(smb_request_t *sr)
 {
         smb_session_t *s = sr->session;
-        int i, rc;
+        int rc;
         uint16_t struct_size;
         uint16_t best_version;
         uint16_t version_cnt;
         uint16_t cl_versions[8];
 

@@ -184,92 +223,101 @@
         if (rc != 0)
                 return (rc);
 
         if ((sr->smb2_cmd_code != SMB2_NEGOTIATE) ||
             (sr->smb2_next_command != 0))
-                return (SDRC_DROP_VC);
+                return (-1);
 
         /*
          * Decode SMB2 Negotiate (fixed-size part)
          */
         rc = smb_mbc_decodef(
-            &sr->command, "www..l16.8.",
+            &sr->command, "www..l16c8.",
             &struct_size,       /* w */
             &version_cnt,       /* w */
-            &s->secmode,        /* w */
+            &s->cli_secmode,    /* w */
             /* reserved         (..) */
-            &s->capabilities);  /* l */
-            /* clnt_uuid         16. */
+            &s->capabilities,   /* l */
+            s->clnt_uuid);      /* 16c */
             /* start_time         8. */
         if (rc != 0)
                 return (rc);
         if (struct_size != 36 || version_cnt > 8)
-                return (SDRC_DROP_VC);
+                return (-1);
 
         /*
          * Decode SMB2 Negotiate (variable part)
          */
         rc = smb_mbc_decodef(&sr->command,
             "#w", version_cnt, cl_versions);
         if (rc != 0)
-                return (SDRC_DROP_VC);
+                return (rc);
 
+        DTRACE_SMB2_START(op__Negotiate, smb_request_t *, sr);
+
         /*
          * The client offers an array of protocol versions it
          * supports, which we have decoded into cl_versions[].
          * We walk the array and pick the highest supported.
          */
-        best_version = 0;
-        for (i = 0; i < version_cnt; i++)
-                if (smb2_supported_version(s, cl_versions[i]) &&
-                    best_version < cl_versions[i])
-                        best_version = cl_versions[i];
-        if (best_version == 0)
-                return (SDRC_DROP_VC);
+        best_version = smb2_find_best_dialect(s, cl_versions, version_cnt);
+        if (best_version == 0) {
+                cmn_err(CE_NOTE, "clnt %s no supported dialect",
+                    sr->session->ip_addr_str);
+                sr->smb2_status = NT_STATUS_INVALID_PARAMETER;
+                rc = -1;
+                goto errout;
+        }
         s->dialect = best_version;
 
         /* Allow normal SMB2 requests now. */
         s->s_state = SMB_SESSION_STATE_NEGOTIATED;
         s->newrq_func = smb2sr_newrq;
 
         rc = smb2_negotiate_common(sr, best_version);
-        if (rc != 0)
-                return (SDRC_DROP_VC);
 
-        return (0);
+errout:
+        /* sr->smb2_status was set */
+        DTRACE_SMB2_DONE(op__Negotiate, smb_request_t *, sr);
+
+        smb2_send_reply(sr);
+
+        return (rc);
 }
 
 /*
  * Common parts of SMB2 Negotiate, used for both the
  * SMB1-to-SMB2 style, and straight SMB2 style.
- * Do negotiation decisions, encode, send the reply.
+ * Do negotiation decisions and encode the reply.
+ * The caller does the network send.
+ *
+ * Return value is 0 for success, and anything else will
+ * terminate the reader thread (drop the connection).
  */
 static int
 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;
 
         /*
          * Negotiation itself.  First the Security Mode.
-         * The caller stashed the client's secmode in s->secmode,
-         * which we validate, and then replace with the server's
-         * secmode, which is all we care about after this.
          */
         secmode = SMB2_NEGOTIATE_SIGNING_ENABLED;
         if (sr->sr_cfg->skc_signing_required) {
                 secmode |= SMB2_NEGOTIATE_SIGNING_REQUIRED;
                 /* Make sure client at least enables signing. */
-                if ((s->secmode & secmode) == 0) {
+                if ((s->cli_secmode & secmode) == 0) {
                         sr->smb2_status = NT_STATUS_INVALID_PARAMETER;
                 }
         }
-        s->secmode = secmode;
+        s->srv_secmode = secmode;
 
         s->cmd_max_bytes = smb2_tcp_bufsize;
         s->reply_max_bytes = smb2_tcp_bufsize;
 
         /*

@@ -291,36 +339,75 @@
          */
         sr->smb2_hdr_flags = SMB2_FLAGS_SERVER_TO_REDIR;
         (void) smb2_encode_header(sr, B_FALSE);
         if (sr->smb2_status != 0) {
                 smb2sr_put_error(sr, sr->smb2_status);
-                smb2_send_reply(sr);
+                /* smb2_send_reply(sr); in caller */
                 return (-1); /* will drop */
         }
 
+        /*
+         * If the version is 0x2FF, we haven't completed negotiate.
+         * Don't initialize until we have our final request.
+         */
+        if (version != 0x2FF)
+                smb2_sign_init_mech(s);
+
+        /*
+         * [MS-SMB2] 3.3.5.4 Receiving an SMB2 NEGOTIATE Request
+         *
+         * The SMB2.x capabilities are returned without regard for
+         * what capabilities the client provided in the request.
+         * The SMB3.x capabilities returned are the traditional
+         * logical AND of server and client capabilities.
+         *
+         * One additional check: If KCF is missing something we
+         * require for encryption, turn off that capability.
+         */
+        if (s->dialect < SMB_VERS_3_0) {
+                /* SMB 2.x */
+                s->srv_cap = smb2srv_capabilities & SMB_2X_CAPS;
+        } else {
+                /* SMB 3.0 or later */
+                s->srv_cap = smb2srv_capabilities &
+                    (SMB_2X_CAPS | s->capabilities);
+                if ((s->srv_cap & SMB2_CAP_ENCRYPTION) != 0 &&
+                    smb3_encrypt_init_mech(s) != 0) {
+                        s->srv_cap &= ~SMB2_CAP_ENCRYPTION;
+                }
+        }
+
+        /*
+         * 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 */
+            s->srv_secmode,             /* w */
             version,                    /* w */
             0, /* reserved */           /* w */
             UUID_LEN,                   /* # */
             &s->s_cfg.skc_machine_uuid, /* c */
-            smb2srv_capabilities,       /* l */
+            s->srv_cap,                 /* 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 */
             sr->sr_cfg->skc_negtok_len, /* # */
             sr->sr_cfg->skc_negtok);    /* c */
 
-        smb2_send_reply(sr);
+        /* smb2_send_reply(sr); in caller */
 
         (void) ksocket_setsockopt(s->sock, SOL_SOCKET,
             SO_SNDBUF, (const void *)&smb2_tcp_bufsize,
             sizeof (smb2_tcp_bufsize), CRED());
         (void) ksocket_setsockopt(s->sock, SOL_SOCKET,

@@ -344,34 +431,71 @@
 
 /*
  * VALIDATE_NEGOTIATE_INFO [MS-SMB2] 2.2.32.6
  */
 uint32_t
-smb2_fsctl_vneginfo(smb_request_t *sr, smb_fsctl_t *fsctl)
+smb2_nego_validate(smb_request_t *sr, smb_fsctl_t *fsctl)
 {
         smb_session_t *s = sr->session;
         int rc;
 
         /*
          * The spec. says to parse the VALIDATE_NEGOTIATE_INFO here
          * and verify that the original negotiate was not modified.
-         * The only tampering we need worry about is secmode, and
-         * we're not taking that from the client, so don't bother.
+         * The request MUST be signed, and we MUST validate the signature.
          *
          * One interesting requirement here is that we MUST reply
          * with exactly the same information as we returned in our
          * original reply to the SMB2 negotiate on this session.
          * If we don't the client closes the connection.
          */
 
+        /* dialects[8] taken from cl_versions[8] in smb2_newrq_negotiate */
+        uint32_t capabilities;
+        uint16_t secmode, num_dialects, dialects[8];
+        uint8_t clnt_guid[16];
+
+        if ((sr->smb2_hdr_flags & SMB2_FLAGS_SIGNED) == 0)
+                goto drop;
+
+        if (fsctl->InputCount < 24)
+                goto drop;
+
+        (void) smb_mbc_decodef(fsctl->in_mbc, "l16cww",
+            &capabilities, /* l */
+            &clnt_guid, /* 16c */
+            &secmode, /* w */
+            &num_dialects); /* w */
+
+        if (num_dialects == 0 || num_dialects > 8)
+                goto drop;
+        if (secmode != s->cli_secmode)
+                goto drop;
+        if (capabilities != s->capabilities)
+                goto drop;
+        if (memcmp(clnt_guid, s->clnt_uuid, sizeof (clnt_guid)) != 0)
+                goto drop;
+
+        if (fsctl->InputCount < (24 + num_dialects * sizeof (*dialects)))
+                goto drop;
+
+        rc = smb_mbc_decodef(fsctl->in_mbc, "#w", num_dialects, dialects);
+        if (rc != 0)
+                goto drop;
+
+        if (smb2_find_best_dialect(s, dialects, num_dialects) != s->dialect)
+                goto drop;
+
         rc = smb_mbc_encodef(
             fsctl->out_mbc, "l#cww",
-            smb2srv_capabilities,       /* l */
+            s->srv_cap,                 /* l */
             UUID_LEN,                   /* # */
             &s->s_cfg.skc_machine_uuid, /* c */
-            s->secmode,                 /* w */
+            s->srv_secmode,             /* w */
             s->dialect);                /* w */
-        if (rc)
-                return (NT_STATUS_INTERNAL_ERROR);
+        if (rc == 0)
+                return (rc);
 
-        return (0);
+drop:
+        smb_session_disconnect(s);
+        return (NT_STATUS_ACCESS_DENIED);
 }