[PATCH V2] blk-mq: avoid sysfs buffer overflow by too many CPU cores

[Ming Lei <ming.lei@redhat.com>]

It is reported that sysfs buffer overflow can be triggered in case
of too many CPU cores(>841 on 4K PAGE_SIZE) when showing CPUs in
blk_mq_hw_sysfs_cpus_show().

So use cpumap_print_to_pagebuf() to print the info and fix the potential
buffer overflow issue.

Cc: stable@vger.kernel.org
Cc: Mark Ray <mark.ray@hpe.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Fixes: 676141e48af7("blk-mq: don't dump CPU -> hw queue map on driver load")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-sysfs.c | 15 +--------------
 1 file changed, 1 insertion(+), 14 deletions(-)

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index d6e1a9bd7131..4d0d32377ba3 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -166,20 +166,7 @@ static ssize_t blk_mq_hw_sysfs_nr_reserved_tags_show(struct blk_mq_hw_ctx *hctx,
 
 static ssize_t blk_mq_hw_sysfs_cpus_show(struct blk_mq_hw_ctx *hctx, char *page)
 {
-	unsigned int i, first = 1;
-	ssize_t ret = 0;
-
-	for_each_cpu(i, hctx->cpumask) {
-		if (first)
-			ret += sprintf(ret + page, "%u", i);
-		else
-			ret += sprintf(ret + page, ", %u", i);
-
-		first = 0;
-	}
-
-	ret += sprintf(ret + page, "\n");
-	return ret;
+	return cpumap_print_to_pagebuf(true, page, hctx->cpumask);
 }
 
 static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_nr_tags = {
-- 
2.20.1