[PATCH] cifs: fix wsize negotiation for 2.6.39 stable

[Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Prior to 2.6.39, when signing was enabled on a socket the client only
sent single-page writes. This changed with commit ca83ce3d5b, which
made signed and unsigned connections use the same codepaths for write
calls.

This caused a regression when working with windows servers. Windows
machines will reject writes larger than the MaxBufferSize when signing
is active, but does not clear the CAP_LARGE_WRITE_X flag in the
negotiation.

This patch backports 2 patches that fix this problem in 3.0 kernels,
and changes a couple of the constants to values appropriate for the
writeback code in 2.6.39.

Cc: stable-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org
Reported-by: Helge Hafting <helge.hafting-CND4fxrytsY@public.gmane.org>
Signed-off-by: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 fs/cifs/connect.c |   64 ++++++++++++++++++++++++++++++++++++----------------
 1 files changed, 44 insertions(+), 20 deletions(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 5236582..8e78710 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2571,23 +2571,6 @@ static void setup_cifs_sb(struct smb_vol *pvolume_info,
 	else /* default */
 		cifs_sb->rsize = CIFSMaxBufSize;
 
-	if (pvolume_info->wsize > PAGEVEC_SIZE * PAGE_CACHE_SIZE) {
-		cERROR(1, "wsize %d too large, using 4096 instead",
-			  pvolume_info->wsize);
-		cifs_sb->wsize = 4096;
-	} else if (pvolume_info->wsize)
-		cifs_sb->wsize = pvolume_info->wsize;
-	else
-		cifs_sb->wsize = min_t(const int,
-					PAGEVEC_SIZE * PAGE_CACHE_SIZE,
-					127*1024);
-		/* old default of CIFSMaxBufSize was too small now
-		   that SMB Write2 can send multiple pages in kvec.
-		   RFC1001 does not describe what happens when frame
-		   bigger than 128K is sent so use that as max in
-		   conjunction with 52K kvec constraint on arch with 4K
-		   page size  */
-
 	if (cifs_sb->rsize < 2048) {
 		cifs_sb->rsize = 2048;
 		/* Windows ME may prefer this */
@@ -2665,6 +2648,48 @@ static void setup_cifs_sb(struct smb_vol *pvolume_info,
 			   "mount option supported");
 }
 
+/* Prior to 3.0, cifs couldn't handle writes larger than this */
+#define CIFS_MAX_WSIZE (PAGEVEC_SIZE * PAGE_CACHE_SIZE)
+
+/*
+ * When the server doesn't allow large posix writes, only allow a wsize of
+ * 128k minus the size of the WRITE_AND_X header. That allows for a write up
+ * to the maximum size described by RFC1002.
+ */
+#define CIFS_MAX_RFC1002_WSIZE (128 * 1024 - sizeof(WRITE_REQ) + 4)
+
+/* Make the default the same as the max */
+#define CIFS_DEFAULT_WSIZE CIFS_MAX_WSIZE
+
+static unsigned int
+cifs_negotiate_wsize(struct cifsTconInfo *tcon, struct smb_vol *pvolume_info)
+{
+	__u64 unix_cap = le64_to_cpu(tcon->fsUnixInfo.Capability);
+	struct TCP_Server_Info *server = tcon->ses->server;
+	unsigned int wsize = pvolume_info->wsize ? pvolume_info->wsize :
+				CIFS_DEFAULT_WSIZE;
+
+	/* can server support 24-bit write sizes? (via UNIX extensions) */
+	if (!tcon->unix_ext || !(unix_cap & CIFS_UNIX_LARGE_WRITE_CAP))
+		wsize = min_t(unsigned int, wsize, CIFS_MAX_RFC1002_WSIZE);
+
+	/*
+	 * no CAP_LARGE_WRITE_X or is signing enabled without CAP_UNIX set?
+	 * Limit it to max buffer offered by the server, minus the size of the
+	 * WRITEX header, not including the 4 byte RFC1001 length.
+	 */
+	if (!(server->capabilities & CAP_LARGE_WRITE_X) ||
+	    (!(server->capabilities & CAP_UNIX) &&
+	     (server->sec_mode & (SECMODE_SIGN_ENABLED|SECMODE_SIGN_REQUIRED))))
+		wsize = min_t(unsigned int, wsize,
+				server->maxBuf - sizeof(WRITE_REQ) + 4);
+
+	/* hard limit of CIFS_MAX_WSIZE */
+	wsize = min_t(unsigned int, wsize, CIFS_MAX_WSIZE);
+
+	return wsize;
+}
+
 static int
 is_path_accessible(int xid, struct cifsTconInfo *tcon,
 		   struct cifs_sb_info *cifs_sb, const char *full_path)
@@ -2866,13 +2891,12 @@ try_mount_again:
 		cifs_sb->rsize = 1024 * 127;
 		cFYI(DBG2, "no very large read support, rsize now 127K");
 	}
-	if (!(tcon->ses->capabilities & CAP_LARGE_WRITE_X))
-		cifs_sb->wsize = min(cifs_sb->wsize,
-			       (tcon->ses->server->maxBuf - MAX_CIFS_HDR_SIZE));
 	if (!(tcon->ses->capabilities & CAP_LARGE_READ_X))
 		cifs_sb->rsize = min(cifs_sb->rsize,
 			       (tcon->ses->server->maxBuf - MAX_CIFS_HDR_SIZE));
 
+	cifs_sb->wsize = cifs_negotiate_wsize(tcon, volume_info);
+
 remote_path_check:
 	/* check if a whole path (including prepath) is not remote */
 	if (!rc && tcon) {
-- 
1.7.5.4