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 <dan.carpenter@oracle.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 129a82f707df..a685c8a79578 100644
--- a/lib/scatterlist.c
+++ b/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 {