Commit 3ebc4397 authored by Waiman Long's avatar Waiman Long Committed by Linus Torvalds
Browse files

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@redhat.com


Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
Reviewed-by: default avatarSergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: default avatarRafael Aquini <aquini@redhat.com>
Acked-by: default avatarMike Rapoport <rppt@linux.ibm.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ef62c8ff

mm/page_owner.c

+3 −11
Original line number Diff line number Diff line
@@ -338,19 +338,16 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, 
	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_t count, unsigned long pfn, 
			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");