lustre: Correct KUC code max changelog msg size

The kernel to userspace communication routines (KUC) allocate
and limit the maximum cs_buf size to CR_MAXSIZE.  However this
fails to account for the fact that the buffer is assumed to begin
with a struct kuc_hdr.  To allocate and account for that space,
we introduce a new define, KUC_CHANGELOG_MSG_MAXSIZE.

Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>
Reviewed-on: http://review.whamcloud.com/7406
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3587
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/include/linux/libcfs/libcfs_kernelcomm.h

@@ -61,6 +61,8 @@ struct kuc_hdr {
 	__u16 kuc_msglen;     /* Including header */
 } __attribute__((aligned(sizeof(__u64))));
 
+#define KUC_CHANGELOG_MSG_MAXSIZE (sizeof(struct kuc_hdr)+CR_MAXSIZE)
+
 #define KUC_MAGIC  0x191C /*Lustre9etLinC */
 #define KUC_FL_BLOCK 0x01   /* Wait for send */
 

drivers/staging/lustre/lustre/mdc/mdc_request.c

@@ -1430,7 +1430,7 @@ static struct kuc_hdr *changelog_kuc_hdr(char *buf, int len, int flags)
 {
 	struct kuc_hdr *lh = (struct kuc_hdr *)buf;
 
-	LASSERT(len <= CR_MAXSIZE);
+	LASSERT(len <= KUC_CHANGELOG_MSG_MAXSIZE);
 
 	lh->kuc_magic = KUC_MAGIC;
 	lh->kuc_transport = KUC_TRANSPORT_CHANGELOG;
@@ -1503,7 +1503,7 @@ static int mdc_changelog_send_thread(void *csdata)
 	CDEBUG(D_CHANGELOG, "changelog to fp=%p start "LPU64"\n",
 	       cs->cs_fp, cs->cs_startrec);
 
-	OBD_ALLOC(cs->cs_buf, CR_MAXSIZE);
+	OBD_ALLOC(cs->cs_buf, KUC_CHANGELOG_MSG_MAXSIZE);
 	if (cs->cs_buf == NULL)
 		GOTO(out, rc = -ENOMEM);
 
@@ -1540,7 +1540,7 @@ out:
 	if (ctxt)
 		llog_ctxt_put(ctxt);
 	if (cs->cs_buf)
-		OBD_FREE(cs->cs_buf, CR_MAXSIZE);
+		OBD_FREE(cs->cs_buf, KUC_CHANGELOG_MSG_MAXSIZE);
 	OBD_FREE_PTR(cs);
 	return rc;
 }