xfs: prevent kernel crash due to corrupted inode log format

Andras Korn reported an oops on log replay causes by a corrupted
xfs_inode_log_format_t passing a 0 size to kmem_zalloc.  This patch handles
to small or too large numbers of log regions gracefully by rejecting the
log replay with a useful error message.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Andras Korn <korn-sgi.com@chardonnay.math.bme.hu>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Felix Blyakher <felixb@sgi.com>

fs/xfs/xfs_log_recover.c

@@ -1455,10 +1455,19 @@ xlog_recover_add_to_trans(
 	item = item->ri_prev;
 
 	if (item->ri_total == 0) {		/* first region to be added */
-		item->ri_total	= in_f->ilf_size;
-		ASSERT(item->ri_total <= XLOG_MAX_REGIONS_IN_ITEM);
-		item->ri_buf = kmem_zalloc((item->ri_total *
-					    sizeof(xfs_log_iovec_t)), KM_SLEEP);
+		if (in_f->ilf_size == 0 ||
+		    in_f->ilf_size > XLOG_MAX_REGIONS_IN_ITEM) {
+			xlog_warn(
+	"XFS: bad number of regions (%d) in inode log format",
+				  in_f->ilf_size);
+			ASSERT(0);
+			return XFS_ERROR(EIO);
+		}
+
+		item->ri_total = in_f->ilf_size;
+		item->ri_buf =
+			kmem_zalloc(item->ri_total * sizeof(xfs_log_iovec_t),
+				    KM_SLEEP);
 	}
 	ASSERT(item->ri_total > item->ri_cnt);
 	/* Description region is ri_buf[0] */