From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: [PATCH v4 2/4] mm/page_owner: Use scnprintf() to avoid excessive buffer overrun check Date: Wed, 2 Feb 2022 15:30:34 -0500 Message-ID: <20220202203036.744010-3-longman@redhat.com> References: <20220131192308.608837-5-longman@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1643834036; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=aswR5jLflKHAA/2KWO7s8HDPhJp/8ybDJLjB9qtlMrw=; b=MdeCq5j1htWObePAKRcyAaAJBSPWZrfBjH+gkdGjaq0+scBNHLQJIyA0wk5e+WKPB6Bp/N rAT88O9qRQs3zTJwqubIEvPvEIW5O1nsqts4WJtN1LapVMj/9EWhcTVwpte4gy+9X+vszO WtGaGK5W3P0ipfNLbwjFtIykdzN+8VE= In-Reply-To: <20220131192308.608837-5-longman@redhat.com> List-ID: Content-Type: text/plain; charset="us-ascii" To: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Ira Weiny , Mike Rapoport , David Rientjes , Roman Gushchin , Rafael Aquini , Waiman Long 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(). Signed-off-by: Waiman Long Acked-by: David Rientjes Reviewed-by: Sergey Senozhatsky --- mm/page_owner.c | 14 +++----------- 1 file changed, 3 insertions(+), 11 deletions(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index 99e360df9465..28dac73e0542 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -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"); -- 2.27.0