block: prevent division by zero in blk_rq_stat_sum()

jira LE-1907
cve CVE-2024-35925
Rebuild_History Non-Buildable kernel-4.18.0-553.16.1.el8_10
commit-author Roman Smirnov <[email protected]>
commit 93f52fb

The expression dst->nr_samples + src->nr_samples may
have zero value on overflow. It is necessary to add
a check to avoid division by zero.

Found by Linux Verification Center (linuxtesting.org) with Svace.

	Signed-off-by: Roman Smirnov <[email protected]>
	Reviewed-by: Sergey Shtylyov <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
	Signed-off-by: Jens Axboe <[email protected]>
(cherry picked from commit 93f52fb)
	Signed-off-by: Jonathan Maple <[email protected]>

Author: PlaidCat

block/blk-stat.c

@@ -27,7 +27,7 @@ void blk_rq_stat_init(struct blk_rq_stat *stat)
 /* src is a per-cpu stat, mean isn't initialized */
 void blk_rq_stat_sum(struct blk_rq_stat *dst, struct blk_rq_stat *src)
 {
-	if (!src->nr_samples)
+	if (dst->nr_samples + src->nr_samples <= dst->nr_samples)
 		return;
 
 	dst->min = min(dst->min, src->min);