From: Waiman Long <longman@xxxxxxxxxx> 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/20220202203036.744010-3-longman@xxxxxxxxxx Signed-off-by: Waiman Long <longman@xxxxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> Acked-by: Rafael Aquini <aquini@xxxxxxxxxx> Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Cc: Ira Weiny <ira.weiny@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Petr Mladek <pmladek@xxxxxxxx> Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx> Cc: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_owner.c | 14 +++----------- 1 file changed, 3 insertions(+), 11 deletions(-) --- 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"); _
