lib/scatterlist: error handling in __sg_alloc_table()

I was reviewing code which I suspected might allocate a zero size SG
table.  That will cause memory corruption.  Also we can't return before
doing the memset or we could end up using uninitialized memory in the
cleanup path.

Signed-off-by: Dan Carpenter <[email protected]>
Cc: Akinobu Mita <[email protected]>
Cc: Imre Deak <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Maxim Levitsky <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Dan Carpenter

lib/scatterlist.c

@@ -247,13 +247,15 @@ int __sg_alloc_table(struct sg_table *table, unsigned int nents,
 	struct scatterlist *sg, *prv;
 	unsigned int left;
 
+	memset(table, 0, sizeof(*table));
+
+	if (nents == 0)
+		return -EINVAL;
 #ifndef ARCH_HAS_SG_CHAIN
 	if (WARN_ON_ONCE(nents > max_ents))
 		return -EINVAL;
 #endif
 
-	memset(table, 0, sizeof(*table));
-
 	left = nents;
 	prv = NULL;
 	do {