This patch set tries to fix that client might oops if nbd server send
unexpected message to client, for example, our syzkaller report a uaf
in nbd_read_stat():
Call trace:
dump_backtrace+0x0/0x310 arch/arm64/kernel/time.c:78
show_stack+0x28/0x38 arch/arm64/kernel/traps.c:158
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x144/0x1b4 lib/dump_stack.c:118
print_address_description+0x68/0x2d0 mm/kasan/report.c:253
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report+0x134/0x2f0 mm/kasan/report.c:409
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
__asan_load4+0x88/0xb0 mm/kasan/kasan.c:699
__read_once_size include/linux/compiler.h:193 [inline]
blk_mq_rq_state block/blk-mq.h:106 [inline]
blk_mq_request_started+0x24/0x40 block/blk-mq.c:644
nbd_read_stat drivers/block/nbd.c:670 [inline]
recv_work+0x1bc/0x890 drivers/block/nbd.c:749
process_one_work+0x3ec/0x9e0 kernel/workqueue.c:2147
worker_thread+0x80/0x9d0 kernel/workqueue.c:2302
kthread+0x1d8/0x1e0 kernel/kthread.c:255
ret_from_fork+0x10/0x18 arch/arm64/kernel/entry.S:1174
1) At first, a normal io is submitted and completed with scheduler:
internel_tag = blk_mq_get_tag -> get tag from sched_tags
blk_mq_rq_ctx_init
sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag]
...
blk_mq_get_driver_tag
__blk_mq_get_driver_tag -> get tag from tags
tags->rq[tag] = sched_tag->static_rq[internel_tag]
So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing
to the request: sched_tags->static_rq[internal_tag]. Even if the
io is finished.
2) nbd server send a reply with random tag directly:
recv_work
nbd_read_stat
blk_mq_tag_to_rq(tags, tag)
rq = tags->rq[tag]
3) if the sched_tags->static_rq is freed:
blk_mq_sched_free_requests
blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i)
-> step 2) access rq before clearing rq mapping
blk_mq_clear_rq_mapping(set, tags, hctx_idx);
__free_pages() -> rq is freed here
4) Then, nbd continue to use the freed request in nbd_read_stat()
Changes in v7:
- instead of exposing blk_queue_exit(), using percpu_ref_put()
directly.
- drop the ref right after nbd_handle_reply().
Changes in v6:
- don't set cmd->status to error if request is completed before
nbd_clear_req().
- get 'q_usage_counter' to prevent accessing freed request through
blk_mq_tag_to_rq(), instead of using blk_mq_find_and_get_req().
Changes in v5:
- move patch 1 & 2 in v4 (patch 4 & 5 in v5) behind
- add some comment in patch 5
Changes in v4:
- change the name of the patchset, since uaf is not the only problem
if server send unexpected reply message.
- instead of adding new interface, use blk_mq_find_and_get_req().
- add patch 5 to this series
Changes in v3:
- v2 can't fix the problem thoroughly, add patch 3-4 to this series.
- modify descriptions.
- patch 5 is just a cleanup
Changes in v2:
- as Bart suggested, add a new helper function for drivers to get
request by tag.
Yu Kuai (6):
nbd: don't handle response without a corresponding request message
nbd: make sure request completion won't concurrent
nbd: check sock index in nbd_read_stat()
nbd: don't start request if nbd_queue_rq() failed
nbd: partition nbd_read_stat() into nbd_read_reply() and
nbd_handle_reply()
nbd: fix uaf in nbd_handle_reply()
drivers/block/nbd.c | 128 ++++++++++++++++++++++++++++++++------------
1 file changed, 94 insertions(+), 34 deletions(-)
--
2.31.1
While handling a response message from server, nbd_read_stat() will
try to get request by tag, and then complete the request. However,
this is problematic if nbd haven't sent a corresponding request
message:
t1 t2
submit_bio
nbd_queue_rq
blk_mq_start_request
recv_work
nbd_read_stat
blk_mq_tag_to_rq
blk_mq_complete_request
nbd_send_cmd
Thus add a new cmd flag 'NBD_CMD_INFLIGHT', it will be set in
nbd_send_cmd() and checked in nbd_read_stat().
Noted that this patch can't fix that blk_mq_tag_to_rq() might
return a freed request, and this will be fixed in following
patches.
Signed-off-by: Yu Kuai <redacted>
Reviewed-by: Ming Lei <redacted>
---
drivers/block/nbd.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
commit cddce0116058 ("nbd: Aovid double completion of a request")
try to fix that nbd_clear_que() and recv_work() can complete a
request concurrently. However, the problem still exists:
t1 t2 t3
nbd_disconnect_and_put
flush_workqueue
recv_work
blk_mq_complete_request
blk_mq_complete_request_remote -> this is true
WRITE_ONCE(rq->state, MQ_RQ_COMPLETE)
blk_mq_raise_softirq
blk_done_softirq
blk_complete_reqs
nbd_complete_rq
blk_mq_end_request
blk_mq_free_request
WRITE_ONCE(rq->state, MQ_RQ_IDLE)
nbd_clear_que
blk_mq_tagset_busy_iter
nbd_clear_req
__blk_mq_free_request
blk_mq_put_tag
blk_mq_complete_request -> complete again
There are three places where request can be completed in nbd:
recv_work(), nbd_clear_que() and nbd_xmit_timeout(). Since they
all hold cmd->lock before completing the request, it's easy to
avoid the problem by setting and checking a cmd flag.
Signed-off-by: Yu Kuai <redacted>
---
drivers/block/nbd.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
Currently, blk_mq_end_request() will be called if nbd_queue_rq()
failed, thus start request in such situation is useless.
Signed-off-by: Yu Kuai <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
drivers/block/nbd.c | 3 ---
1 file changed, 3 deletions(-)
@@ -934,7 +934,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)if(!refcount_inc_not_zero(&nbd->config_refs)){dev_err_ratelimited(disk_to_dev(nbd->disk),"Socks array is empty\n");-blk_mq_start_request(req);return-EINVAL;}config=nbd->config;
@@ -943,7 +942,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)dev_err_ratelimited(disk_to_dev(nbd->disk),"Attempted send on invalid socket\n");nbd_config_put(nbd);-blk_mq_start_request(req);return-EINVAL;}cmd->status=BLK_STS_OK;
@@ -967,7 +965,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)*/sock_shutdown(nbd);nbd_config_put(nbd);-blk_mq_start_request(req);return-EIO;}gotoagain;
The sock that clent send request in nbd_send_cmd() and receive reply
in nbd_read_stat() should be the same.
Signed-off-by: Yu Kuai <redacted>
---
drivers/block/nbd.c | 4 ++++
1 file changed, 4 insertions(+)
There is a problem that nbd_handle_reply() might access freed request:
1) At first, a normal io is submitted and completed with scheduler:
internel_tag = blk_mq_get_tag -> get tag from sched_tags
blk_mq_rq_ctx_init
sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag]
...
blk_mq_get_driver_tag
__blk_mq_get_driver_tag -> get tag from tags
tags->rq[tag] = sched_tag->static_rq[internel_tag]
So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing
to the request: sched_tags->static_rq[internal_tag]. Even if the
io is finished.
2) nbd server send a reply with random tag directly:
recv_work
nbd_handle_reply
blk_mq_tag_to_rq(tags, tag)
rq = tags->rq[tag]
3) if the sched_tags->static_rq is freed:
blk_mq_sched_free_requests
blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i)
-> step 2) access rq before clearing rq mapping
blk_mq_clear_rq_mapping(set, tags, hctx_idx);
__free_pages() -> rq is freed here
4) Then, nbd continue to use the freed request in nbd_handle_reply
Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(),
thus request is ensured not to be freed because 'q_usage_counter' is
not zero.
Signed-off-by: Yu Kuai <redacted>
---
drivers/block/nbd.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
On Wed, Sep 15, 2021 at 05:20:06PM +0800, Yu Kuai wrote:
commit cddce0116058 ("nbd: Aovid double completion of a request")
try to fix that nbd_clear_que() and recv_work() can complete a
request concurrently. However, the problem still exists:
t1 t2 t3
nbd_disconnect_and_put
flush_workqueue
recv_work
blk_mq_complete_request
blk_mq_complete_request_remote -> this is true
WRITE_ONCE(rq->state, MQ_RQ_COMPLETE)
blk_mq_raise_softirq
blk_done_softirq
blk_complete_reqs
nbd_complete_rq
blk_mq_end_request
blk_mq_free_request
WRITE_ONCE(rq->state, MQ_RQ_IDLE)
nbd_clear_que
blk_mq_tagset_busy_iter
nbd_clear_req
__blk_mq_free_request
blk_mq_put_tag
blk_mq_complete_request -> complete again
There are three places where request can be completed in nbd:
recv_work(), nbd_clear_que() and nbd_xmit_timeout(). Since they
all hold cmd->lock before completing the request, it's easy to
avoid the problem by setting and checking a cmd flag.
Signed-off-by: Yu Kuai <redacted>
---
On Wed, Sep 15, 2021 at 05:20:08PM +0800, Yu Kuai wrote:
quoted hunk
Currently, blk_mq_end_request() will be called if nbd_queue_rq()
failed, thus start request in such situation is useless.
Signed-off-by: Yu Kuai <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
drivers/block/nbd.c | 3 ---
1 file changed, 3 deletions(-)
@@ -934,7 +934,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)if(!refcount_inc_not_zero(&nbd->config_refs)){dev_err_ratelimited(disk_to_dev(nbd->disk),"Socks array is empty\n");-blk_mq_start_request(req);return-EINVAL;}config=nbd->config;
@@ -943,7 +942,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)dev_err_ratelimited(disk_to_dev(nbd->disk),"Attempted send on invalid socket\n");nbd_config_put(nbd);-blk_mq_start_request(req);return-EINVAL;}cmd->status=BLK_STS_OK;
@@ -967,7 +965,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)*/sock_shutdown(nbd);nbd_config_put(nbd);-blk_mq_start_request(req);return-EIO;}
It is basically a partial revert of the following fix, care to add commit log
about why removing these blk_mq_start_request() is safe?
commit 6a468d5990ecd1c2d07dd85f8633bbdd0ba61c40
Author: Josef Bacik [off-list ref]
Date: Mon Nov 6 16:11:58 2017 -0500
nbd: don't start req until after the dead connection logic
Thanks,
Ming
On Wed, Sep 15, 2021 at 05:20:10PM +0800, Yu Kuai wrote:
quoted hunk
There is a problem that nbd_handle_reply() might access freed request:
1) At first, a normal io is submitted and completed with scheduler:
internel_tag = blk_mq_get_tag -> get tag from sched_tags
blk_mq_rq_ctx_init
sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag]
...
blk_mq_get_driver_tag
__blk_mq_get_driver_tag -> get tag from tags
tags->rq[tag] = sched_tag->static_rq[internel_tag]
So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing
to the request: sched_tags->static_rq[internal_tag]. Even if the
io is finished.
2) nbd server send a reply with random tag directly:
recv_work
nbd_handle_reply
blk_mq_tag_to_rq(tags, tag)
rq = tags->rq[tag]
3) if the sched_tags->static_rq is freed:
blk_mq_sched_free_requests
blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i)
-> step 2) access rq before clearing rq mapping
blk_mq_clear_rq_mapping(set, tags, hctx_idx);
__free_pages() -> rq is freed here
4) Then, nbd continue to use the freed request in nbd_handle_reply
Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(),
thus request is ensured not to be freed because 'q_usage_counter' is
not zero.
Signed-off-by: Yu Kuai <redacted>
---
drivers/block/nbd.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
The above comment is wrong, the purpose is simply for avoiding request
pool freed, such as elevator switching won't happen once
->q_usage_counter is grabbed. So no any request UAF can be triggered
when calling into nbd_handle_reply().
+ if (!percpu_ref_tryget(&q->q_usage_counter)) {
+ dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
+ __func__);
+ break;
+ }
+
cmd = nbd_handle_reply(nbd, args->index, &reply);
+ /*
+ * It's safe to drop ref before request completion, inflight
+ * request will ensure q_usage_counter won't be zero.
+ */
On Wed, Sep 15, 2021 at 05:20:10PM +0800, Yu Kuai wrote:
quoted
There is a problem that nbd_handle_reply() might access freed request:
1) At first, a normal io is submitted and completed with scheduler:
internel_tag = blk_mq_get_tag -> get tag from sched_tags
blk_mq_rq_ctx_init
sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag]
...
blk_mq_get_driver_tag
__blk_mq_get_driver_tag -> get tag from tags
tags->rq[tag] = sched_tag->static_rq[internel_tag]
So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing
to the request: sched_tags->static_rq[internal_tag]. Even if the
io is finished.
2) nbd server send a reply with random tag directly:
recv_work
nbd_handle_reply
blk_mq_tag_to_rq(tags, tag)
rq = tags->rq[tag]
3) if the sched_tags->static_rq is freed:
blk_mq_sched_free_requests
blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i)
-> step 2) access rq before clearing rq mapping
blk_mq_clear_rq_mapping(set, tags, hctx_idx);
__free_pages() -> rq is freed here
4) Then, nbd continue to use the freed request in nbd_handle_reply
Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(),
thus request is ensured not to be freed because 'q_usage_counter' is
not zero.
Signed-off-by: Yu Kuai <redacted>
---
drivers/block/nbd.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
The above comment is wrong, the purpose is simply for avoiding request
pool freed, such as elevator switching won't happen once
->q_usage_counter is grabbed. So no any request UAF can be triggered
when calling into nbd_handle_reply().
Do you mean the comment about q_usage_counter is zero is wrong ?
quoted
+ if (!percpu_ref_tryget(&q->q_usage_counter)) {
+ dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
+ __func__);
+ break;
+ }
+
cmd = nbd_handle_reply(nbd, args->index, &reply);
+ /*
+ * It's safe to drop ref before request completion, inflight
+ * request will ensure q_usage_counter won't be zero.
+ */
On Thu, Sep 16, 2021 at 04:47:08PM +0800, yukuai (C) wrote:
On 2021/09/16 16:04, Ming Lei wrote:
quoted
On Wed, Sep 15, 2021 at 05:20:10PM +0800, Yu Kuai wrote:
quoted
There is a problem that nbd_handle_reply() might access freed request:
1) At first, a normal io is submitted and completed with scheduler:
internel_tag = blk_mq_get_tag -> get tag from sched_tags
blk_mq_rq_ctx_init
sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag]
...
blk_mq_get_driver_tag
__blk_mq_get_driver_tag -> get tag from tags
tags->rq[tag] = sched_tag->static_rq[internel_tag]
So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing
to the request: sched_tags->static_rq[internal_tag]. Even if the
io is finished.
2) nbd server send a reply with random tag directly:
recv_work
nbd_handle_reply
blk_mq_tag_to_rq(tags, tag)
rq = tags->rq[tag]
3) if the sched_tags->static_rq is freed:
blk_mq_sched_free_requests
blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i)
-> step 2) access rq before clearing rq mapping
blk_mq_clear_rq_mapping(set, tags, hctx_idx);
__free_pages() -> rq is freed here
4) Then, nbd continue to use the freed request in nbd_handle_reply
Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(),
thus request is ensured not to be freed because 'q_usage_counter' is
not zero.
Signed-off-by: Yu Kuai <redacted>
---
drivers/block/nbd.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
The above comment is wrong, the purpose is simply for avoiding request
pool freed, such as elevator switching won't happen once
->q_usage_counter is grabbed. So no any request UAF can be triggered
when calling into nbd_handle_reply().
Do you mean the comment about q_usage_counter is zero is wrong ?
How about the following words?
/*
* Grab .q_usage_counter so request pool won't go away, then no request
* use-after-free is possible during nbd_handle_reply(). If queue is frozen,
* there won't be any inflight requests, we needn't to handle the incoming
* garbage message
*/
Thanks,
Ming
On Thu, Sep 16, 2021 at 04:47:08PM +0800, yukuai (C) wrote:
quoted
On 2021/09/16 16:04, Ming Lei wrote:
quoted
On Wed, Sep 15, 2021 at 05:20:10PM +0800, Yu Kuai wrote:
quoted
There is a problem that nbd_handle_reply() might access freed request:
1) At first, a normal io is submitted and completed with scheduler:
internel_tag = blk_mq_get_tag -> get tag from sched_tags
blk_mq_rq_ctx_init
sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag]
...
blk_mq_get_driver_tag
__blk_mq_get_driver_tag -> get tag from tags
tags->rq[tag] = sched_tag->static_rq[internel_tag]
So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing
to the request: sched_tags->static_rq[internal_tag]. Even if the
io is finished.
2) nbd server send a reply with random tag directly:
recv_work
nbd_handle_reply
blk_mq_tag_to_rq(tags, tag)
rq = tags->rq[tag]
3) if the sched_tags->static_rq is freed:
blk_mq_sched_free_requests
blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i)
-> step 2) access rq before clearing rq mapping
blk_mq_clear_rq_mapping(set, tags, hctx_idx);
__free_pages() -> rq is freed here
4) Then, nbd continue to use the freed request in nbd_handle_reply
Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(),
thus request is ensured not to be freed because 'q_usage_counter' is
not zero.
Signed-off-by: Yu Kuai <redacted>
---
drivers/block/nbd.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
The above comment is wrong, the purpose is simply for avoiding request
pool freed, such as elevator switching won't happen once
->q_usage_counter is grabbed. So no any request UAF can be triggered
when calling into nbd_handle_reply().
Do you mean the comment about q_usage_counter is zero is wrong ?
How about the following words?
/*
* Grab .q_usage_counter so request pool won't go away, then no request
* use-after-free is possible during nbd_handle_reply(). If queue is frozen,
* there won't be any inflight requests, we needn't to handle the incoming
* garbage message
*/