[010/114] mm/page_owner: use scnprintf() to avoid excessive buffer overrun check

Commit Message

Andrew Morton March 25, 2022, 1:09 a.m. UTC

From: Waiman Long <[e-mail]>
Subject: mm/page_owner: use scnprintf() to avoid excessive buffer overrun check

The snprintf() function can return a length greater than the given input
size.  That will require a check for buffer overrun after each invocation
of snprintf().  scnprintf(), on the other hand, will never return a
greater length.  By using scnprintf() in selected places, we can avoid
some buffer overrun checks except after stack_depot_snprint() and after
the last snprintf().

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Waiman Long <[e-mail]>
Acked-by: David Rientjes <[e-mail]>
Reviewed-by: Sergey Senozhatsky <[e-mail]>
Acked-by: Rafael Aquini <[e-mail]>
Acked-by: Mike Rapoport <[e-mail]>
Cc: Andy Shevchenko <[e-mail]>
Cc: Ira Weiny <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Petr Mladek <[e-mail]>
Cc: Rasmus Villemoes <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Steven Rostedt (Google) <[e-mail]>
Cc: Vladimir Davydov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/page_owner.c |   14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

Patch

--- a/mm/page_owner.c~mm-page_owner-use-scnprintf-to-avoid-excessive-buffer-overrun-check
+++ a/mm/page_owner.c
@@ -338,19 +338,16 @@  print_page_owner(char __user *buf, size_
 	if (!kbuf)
 		return -ENOMEM;
 
-	ret = snprintf(kbuf, count,
+	ret = scnprintf(kbuf, count,
 			"Page allocated via order %u, mask %#x(%pGg), pid %d, ts %llu ns, free_ts %llu ns\n",
 			page_owner->order, page_owner->gfp_mask,
 			&page_owner->gfp_mask, page_owner->pid,
 			page_owner->ts_nsec, page_owner->free_ts_nsec);
 
-	if (ret >= count)
-		goto err;
-
 	/* Print information relevant to grouping pages by mobility */
 	pageblock_mt = get_pageblock_migratetype(page);
 	page_mt  = gfp_migratetype(page_owner->gfp_mask);
-	ret += snprintf(kbuf + ret, count - ret,
+	ret += scnprintf(kbuf + ret, count - ret,
 			"PFN %lu type %s Block %lu type %s Flags %pGp\n",
 			pfn,
 			migratetype_names[page_mt],
@@ -358,19 +355,14 @@  print_page_owner(char __user *buf, size_
 			migratetype_names[pageblock_mt],
 			&page->flags);
 
-	if (ret >= count)
-		goto err;
-
 	ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
 	if (ret >= count)
 		goto err;
 
 	if (page_owner->last_migrate_reason != -1) {
-		ret += snprintf(kbuf + ret, count - ret,
+		ret += scnprintf(kbuf + ret, count - ret,
 			"Page has been migrated, last migrate reason: %s\n",
 			migrate_reason_names[page_owner->last_migrate_reason]);
-		if (ret >= count)
-			goto err;
 	}
 
 	ret += snprintf(kbuf + ret, count - ret, "\n");