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Subject[PATCH 3.16.y-ckt 038/133] blk-mq: fix buffer overflow when reading sysfs file of 'pending'
Date
3.16.7-ckt18 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ming Lei <ming.lei@canonical.com>

commit 596f5aad2a704b72934e5abec1b1b4114c16f45b upstream.

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

Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
block/blk-mq-sysfs.c | 25 ++++++++++++++++++-------
1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index e0fb3f4a628f..4bd57a9cf5ff 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);
+
+ 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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