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Message-ID: <710eb24d-801e-b843-d02e-8a5b16b60265@huawei.com>
Date: Fri, 28 Feb 2020 18:14:39 +0800
From: "yukuai (C)" <yukuai3@...wei.com>
To: <axboe@...nel.dk>, <ming.lei@...hat.com>,
<chaitanya.kulkarni@....com>, <damien.lemoal@....com>,
<bvanassche@....org>, <dhowells@...hat.com>,
<asml.silence@...il.com>, <ajay.joshi@....com>
CC: <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<yi.zhang@...wei.com>, <zhangxiaoxu5@...wei.com>,
<luoshijie1@...wei.com>
Subject: Re: [PATCH V2] block: rename 'q->debugfs_dir' and 'q->blk_trace->dir'
in blk_unregister_queue()
ping...
On 2020/2/13 16:12, yu kuai wrote:
> syzbot is reporting use after free bug in debugfs_remove[1].
>
> This is because in request_queue, 'q->debugfs_dir' and
> 'q->blk_trace->dir' could be the same dir. And in __blk_release_queue(),
> blk_mq_debugfs_unregister() will remove everything inside the dir.
>
> With futher investigation of the reporduce repro, the problem can be
> reporduced by following procedure:
>
> 1. LOOP_CTL_ADD, create a request_queue q1, blk_mq_debugfs_register() will
> create the dir.
> 2. LOOP_CTL_REMOVE, blk_release_queue() will add q1 to release queue.
> 3. LOOP_CTL_ADD, create another request_queue q2,blk_mq_debugfs_register()
> will fail because the dir aready exist.
> 4. BLKTRACESETUP, create two files(msg and dropped) inside the dir.
> 5. call __blk_release_queue() for q1, debugfs_remove_recursive() will
> delete the files created in step 4.
> 6. LOOP_CTL_REMOVE, blk_release_queue() will add q2 to release queue.
> And when __blk_release_queue() is called for q2, blk_trace_shutdown() will
> try to release the two files created in step 4, wich are aready released
> in step 5.
>
> thread1 |kworker |thread2
> ----------------------- | ------------------------ | --------------------
> loop_control_ioctl | |
> loop_add | |
> blk_mq_debugfs_register| |
> debugfs_create_dir | |
> loop_control_ioctl | |
> loop_remove | |
> blk_release_queue | |
> schedule_work | |
> | |loop_control_ioctl
> | | loop_add
> | | ...
> | |blk_trace_ioctl
> | | __blk_trace_setup
> | | debugfs_create_file
> |__blk_release_queue |
> | blk_mq_debugfs_unregister|
> | debugfs_remove_recursive|
> | |loop_control_ioctl
> | | loop_remove
> | | ...
> |__blk_release_queue |
> | blk_trace_shutdown |
> | debugfs_remove |
>
> commit dc9edc44de6c ("block: Fix a blk_exit_rl() regression") pushed the
> final release of request_queue to a workqueue, so, when loop_add() is
> called again(step 3), __blk_release_queue() might not been called yet,
> which causes the problem.
>
> Fix the problem by renaming 'q->debugfs_dir' or 'q->blk_trace->dir'
> in blk_unregister_queue() if they exist.
>
> [1] https://syzkaller.appspot.com/bug?extid=903b72a010ad6b7a40f2
> References: CVE-2019-19770
> Fixes: commit dc9edc44de6c ("block: Fix a blk_exit_rl() regression")
> Reported-by: syzbot <syz...@...kaller.appspotmail.com>
> Signed-off-by: yu kuai <yukuai3@...wei.com>
> ---
> Changes in V2:
> add device name to the new dir name
> fix compile err when 'CONFIG_BLK_DEBUG_FS' is not enabled
> add treatment of 'q->blk_trace->dir'
>
> block/blk-sysfs.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 42 insertions(+)
>
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index fca9b158f4a0..1da8d4a4915a 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -11,6 +11,7 @@
> #include <linux/blktrace_api.h>
> #include <linux/blk-mq.h>
> #include <linux/blk-cgroup.h>
> +#include <linux/debugfs.h>
>
> #include "blk.h"
> #include "blk-mq.h"
> @@ -1011,6 +1012,46 @@ int blk_register_queue(struct gendisk *disk)
> }
> EXPORT_SYMBOL_GPL(blk_register_queue);
>
> +#ifdef CONFIG_DEBUG_FS
> +/*
> + * blk_prepare_release_queue - rename q->debugfs_dir and q->blk_trace->dir
> + * @q: request_queue of which the dir to be renamed belong to.
> + *
> + * Because the final release of request_queue is in a workqueue, the
> + * cleanup might not been finished yet while the same device start to
> + * create. It's not correct if q->debugfs_dir still exist while trying
> + * to create a new one.
> + */
> +static void blk_prepare_release_queue(struct request_queue *q)
> +{
> + struct dentry *new = NULL;
> + struct dentry **old = NULL;
> + char name[DNAME_INLINE_LEN];
> + int i = 0;
> +
> +#ifdef CONFIG_BLK_DEBUG_FS
> + if (!IS_ERR_OR_NULL(q->debugfs_dir))
> + old = &q->debugfs_dir;
> +#endif
> +#ifdef CONFIG_BLK_DEV_IO_TRACE
> + /* q->debugfs_dir and q->blk_trace->dir can't both exist */
> + if (q->blk_trace && !IS_ERR_OR_NULL(q->blk_trace->dir))
> + old = &q->blk_trace->dir;
> +#endif
> + if (old == NULL)
> + return;
> + while (new == NULL) {
> + sprintf(name, "ready_to_remove_%s_%d",
> + kobject_name(q->kobj.parent), i++);
> + new = debugfs_rename(blk_debugfs_root, *old,
> + blk_debugfs_root, name);
> + }
> + *old = new;
> +}
> +#else
> +#define blk_prepare_release_queue(q) do { } while (0)
> +#endif
> +
> /**
> * blk_unregister_queue - counterpart of blk_register_queue()
> * @disk: Disk of which the request queue should be unregistered from sysfs.
> @@ -1039,6 +1080,7 @@ void blk_unregister_queue(struct gendisk *disk)
> mutex_unlock(&q->sysfs_lock);
>
> mutex_lock(&q->sysfs_dir_lock);
> + blk_prepare_release_queue(q);
> /*
> * Remove the sysfs attributes before unregistering the queue data
> * structures that can be modified through sysfs.
>
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