From 596f5aad2a704b72934e5abec1b1b4114c16f45b Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Sun, 9 Aug 2015 03:41:50 -0400 Subject: [PATCH] blk-mq: fix buffer overflow when reading sysfs file of 'pending' There may be lots of pending requests so that the buffer of PAGE_SIZE can't hold them at all. One typical example is scsi-mq, the queue depth(.can_queue) of scsi_host and blk-mq is quite big but scsi_device's queue_depth is a bit small(.cmd_per_lun), then it is quite easy to have lots of pending requests in hw queue. This patch fixes the following warning and the related memory destruction. [ 359.025101] fill_read_buffer: blk_mq_hw_sysfs_show+0x0/0x7d returned bad count^M [ 359.055595] irq event stamp: 15537^M [ 359.055606] general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC ^M [ 359.055614] Dumping ftrace buffer:^M [ 359.055660] (ftrace buffer empty)^M [ 359.055672] Modules linked in: nbd ipv6 kvm_intel kvm serio_raw^M [ 359.055678] CPU: 4 PID: 21631 Comm: stress-ng-sysfs Not tainted 4.2.0-rc5-next-20150805 #434^M [ 359.055679] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011^M [ 359.055682] task: ffff8802161cc000 ti: ffff88021b4a8000 task.ti: ffff88021b4a8000^M [ 359.055693] RIP: 0010:[] [] __kmalloc+0xe8/0x152^M Cc: Signed-off-by: Ming Lei Signed-off-by: Jens Axboe --- block/blk-mq-sysfs.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index b79685e06b70..279c5d674edf 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -141,15 +141,26 @@ static ssize_t blk_mq_sysfs_completed_show(struct blk_mq_ctx *ctx, char *page) static ssize_t sysfs_list_show(char *page, struct list_head *list, char *msg) { - char *start_page = page; struct request *rq; + int len = snprintf(page, PAGE_SIZE - 1, "%s:\n", msg); - page += sprintf(page, "%s:\n", msg); + list_for_each_entry(rq, list, queuelist) { + const int rq_len = 2 * sizeof(rq) + 2; - list_for_each_entry(rq, list, queuelist) - page += sprintf(page, "\t%p\n", rq); + /* if the output will be truncated */ + if (PAGE_SIZE - 1 < len + rq_len) { + /* backspacing if it can't hold '\t...\n' */ + if (PAGE_SIZE - 1 < len + 5) + len -= rq_len; + len += snprintf(page + len, PAGE_SIZE - 1 - len, + "\t...\n"); + break; + } + len += snprintf(page + len, PAGE_SIZE - 1 - len, + "\t%p\n", rq); + } - return page - start_page; + return len; } static ssize_t blk_mq_sysfs_rq_list_show(struct blk_mq_ctx *ctx, char *page)