Commit 596f5aad authored Aug 09, 2015 by Ming Lei Committed by Jens Axboe Aug 15, 2015

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:[<ffffffff811541c5>]  [<ffffffff811541c5>] __kmalloc+0xe8/0x152^M

Cc: <stable@vger.kernel.org>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent 2ec3182f

block/blk-mq-sysfs.c

+18 −7

Original line number	Diff line number	Diff line
		@@ -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);

		list_for_each_entry(rq, list, queuelist) {
		const int rq_len = 2 * sizeof(rq) + 2;

		/* 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);
		}

		page += sprintf(page, "%s:\n", msg);

		list_for_each_entry(rq, list, queuelist)
		page += sprintf(page, "\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)

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