From: Steve French <stfrench@microsoft.com>
Date: Wed, 9 Dec 2020 01:12:35 -0600
Subject: [PATCH] SMB3.1.1: remove confusing mount warning when no SPNEGO info
 on negprot rsp
Git-commit: bc7c4129d4cdc56d1b5477c1714246f27df914dd
References: bsc#1190317
Patch-mainline: v5.11-rc1

Azure does not send an SPNEGO blob in the negotiate protocol response,
so we shouldn't assume that it is there when validating the location
of the first negotiate context.  This avoids the potential confusing
mount warning:

   CIFS: Invalid negotiate context offset

[ ematsumiya: context adjustment ]

CC: Stable <stable@vger.kernel.org>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Acked-by: Enzo Matsumiya <ematsumiya@suse.de>
---
 fs/cifs/smb2misc.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

--- a/fs/cifs/smb2misc.c
+++ b/fs/cifs/smb2misc.c
@@ -93,6 +93,8 @@ static const __le16 smb2_rsp_struct_size
 	/* SMB2_OPLOCK_BREAK */ cpu_to_le16(24)
 };
 
+#define SMB311_NEGPROT_BASE_SIZE (sizeof(struct smb2_sync_hdr) + sizeof(struct smb2_negotiate_rsp))
+
 static __u32 get_neg_ctxt_len(struct smb2_sync_hdr *hdr, __u32 len,
 			      __u32 non_ctxlen)
 {
@@ -108,11 +110,17 @@ static __u32 get_neg_ctxt_len(struct smb
 
 	/* Make sure that negotiate contexts start after gss security blob */
 	nc_offset = le32_to_cpu(pneg_rsp->NegotiateContextOffset);
-	if (nc_offset < non_ctxlen) {
-		printk_once(KERN_WARNING "invalid negotiate context offset\n");
+	if (nc_offset + 1 < non_ctxlen) {
+		pr_warn_once("Invalid negotiate context offset %d\n", nc_offset);
 		return 0;
-	}
-	size_of_pad_before_neg_ctxts = nc_offset - non_ctxlen;
+	} else if (nc_offset + 1 == non_ctxlen) {
+		cifs_dbg(FYI, "no SPNEGO security blob in negprot rsp\n");
+		size_of_pad_before_neg_ctxts = 0;
+	} else if (non_ctxlen == SMB311_NEGPROT_BASE_SIZE)
+		/* has padding, but no SPNEGO blob */
+		size_of_pad_before_neg_ctxts = nc_offset - non_ctxlen + 1;
+	else
+		size_of_pad_before_neg_ctxts = nc_offset - non_ctxlen;
 
 	/* Verify that at least minimal negotiate contexts fit within frame */
 	if (len < nc_offset + (neg_count * sizeof(struct smb2_neg_context))) {