[PATCH v3] lib/graph: lib/graph: fix memset with NULL

[Marat Khalili <marat.khalili@huawei.com>]

This was flagged by undefined behaviour sanitizer: memset should not be
called with NULL first argument. (memset requires first argument to be
pointer to a memory object, so passing NULL may result in an undefined
behaviour including among other things optimizer potentially removing
code paths depending on stat->xstat_count being NULL.)

Sanitizer message:

    lib/graph/graph_stats.c:473:2: runtime error: null pointer passed as
    argument 1, which is declared to never be null

Add a check that stat->xstat_cntrs is not zero before the call, since
stat->xstat_count can only be NULL when stat->xstat_cntrs is zero.

Fixes: 070db97e017 ("graph: support node xstats")

Signed-off-by: Marat Khalili <marat.khalili@huawei.com>
---

Thanks to Jerin Jacob and David Marchand for the reviews.

v3:
* Addressing comments from David Marchand change to check the length
instead of the pointer, fix formatting.
* Drop the other half of the two-patch set since the problem it was
addressing was already getting fixed elsewhere.

v2: Following the suggestions from Jerin Jacob changed the Subject and
added Fixes line.

 lib/graph/graph_stats.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/graph/graph_stats.c b/lib/graph/graph_stats.c
index bb202577e9..9e330c8e61 100644
--- a/lib/graph/graph_stats.c
+++ b/lib/graph/graph_stats.c
@@ -470,7 +470,8 @@ cluster_node_arregate_stats(struct cluster_node *cluster, bool dispatch)
 	uint64_t *xstat;
 	uint8_t i;
 
-	memset(stat->xstat_count, 0, sizeof(uint64_t) * stat->xstat_cntrs);
+	if (stat->xstat_cntrs != 0)
+		memset(stat->xstat_count, 0, sizeof(uint64_t) * stat->xstat_cntrs);
 	for (count = 0; count < cluster->nb_nodes; count++) {
 		node = cluster->nodes[count];
 
-- 
2.43.0