* [PATCH] blktrace: Fix uaf in blk_trace access after removing by sysfs
@ 2021-09-10 9:21 Zhihao Cheng
2021-09-22 1:15 ` Zhihao Cheng
2021-09-22 5:21 ` Christoph Hellwig
0 siblings, 2 replies; 4+ messages in thread
From: Zhihao Cheng @ 2021-09-10 9:21 UTC (permalink / raw)
To: axboe, rostedt, mingo, acme
Cc: linux-block, linux-kernel, chengzhihao1, yukuai3
There is an use-after-free problem triggered by following process:
P1(sda) P2(sdb)
echo 0 > /sys/block/sdb/trace/enable
blk_trace_remove_queue
synchronize_rcu
blk_trace_free
relay_close
rcu_read_lock
__blk_add_trace
trace_note_tsk
(Iterate running_trace_list)
relay_close_buf
relay_destroy_buf
kfree(buf)
trace_note(sdb's bt)
relay_reserve
buf->offset <- nullptr deference (use-after-free) !!!
rcu_read_unlock
[ 502.714379] BUG: kernel NULL pointer dereference, address:
0000000000000010
[ 502.715260] #PF: supervisor read access in kernel mode
[ 502.715903] #PF: error_code(0x0000) - not-present page
[ 502.716546] PGD 103984067 P4D 103984067 PUD 17592b067 PMD 0
[ 502.717252] Oops: 0000 [#1] SMP
[ 502.720308] RIP: 0010:trace_note.isra.0+0x86/0x360
[ 502.732872] Call Trace:
[ 502.733193] __blk_add_trace.cold+0x137/0x1a3
[ 502.733734] blk_add_trace_rq+0x7b/0xd0
[ 502.734207] blk_add_trace_rq_issue+0x54/0xa0
[ 502.734755] blk_mq_start_request+0xde/0x1b0
[ 502.735287] scsi_queue_rq+0x528/0x1140
...
[ 502.742704] sg_new_write.isra.0+0x16e/0x3e0
[ 502.747501] sg_ioctl+0x466/0x1100
Reproduce method:
ioctl(/dev/sda, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])
ioctl(/dev/sda, BLKTRACESTART)
ioctl(/dev/sdb, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])
ioctl(/dev/sdb, BLKTRACESTART)
echo 0 > /sys/block/sdb/trace/enable &
// Add delay(mdelay/msleep) before kernel enters blk_trace_free()
ioctl$SG_IO(/dev/sda, SG_IO, ...)
// Enters trace_note_tsk() after blk_trace_free() returned
// Use mdelay in rcu region rather than msleep(which may schedule out)
Don't remove blk_trace by sysfs when blk_trace is at Blktrace_running
state, just like function __blk_trace_remove() does. The state change
process and blk_trace_remove_queue() are protected and by mutex lock
'q->debugfs_mutex', so the sequence of stopping blk_trace first and
then removing it will be ensured.
Fixes: c71a896154119f ("blktrace: add ftrace plugin")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
---
kernel/trace/blktrace.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index c221e4c3f625..7fe29bb9746f 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1821,8 +1821,17 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
}
if (value)
ret = blk_trace_setup_queue(q, bdev);
- else
- ret = blk_trace_remove_queue(q);
+ else {
+ /*
+ * Don't remove blk_trace under running state, in
+ * case triggering use-after-free in function
+ * __blk_add_trace().
+ */
+ if (bt->trace_state != Blktrace_running)
+ ret = blk_trace_remove_queue(q);
+ else
+ ret = -EBUSY;
+ }
goto out_unlock_bdev;
}
--
2.31.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] blktrace: Fix uaf in blk_trace access after removing by sysfs
2021-09-10 9:21 [PATCH] blktrace: Fix uaf in blk_trace access after removing by sysfs Zhihao Cheng
@ 2021-09-22 1:15 ` Zhihao Cheng
2021-09-22 5:21 ` Christoph Hellwig
1 sibling, 0 replies; 4+ messages in thread
From: Zhihao Cheng @ 2021-09-22 1:15 UTC (permalink / raw)
To: axboe, rostedt, mingo, acme; +Cc: linux-block, linux-kernel, yukuai3
在 2021/9/10 17:21, Zhihao Cheng 写道:
friendly ping
> There is an use-after-free problem triggered by following process:
>
> P1(sda) P2(sdb)
> echo 0 > /sys/block/sdb/trace/enable
> blk_trace_remove_queue
> synchronize_rcu
> blk_trace_free
> relay_close
> rcu_read_lock
> __blk_add_trace
> trace_note_tsk
> (Iterate running_trace_list)
> relay_close_buf
> relay_destroy_buf
> kfree(buf)
> trace_note(sdb's bt)
> relay_reserve
> buf->offset <- nullptr deference (use-after-free) !!!
> rcu_read_unlock
>
> [ 502.714379] BUG: kernel NULL pointer dereference, address:
> 0000000000000010
> [ 502.715260] #PF: supervisor read access in kernel mode
> [ 502.715903] #PF: error_code(0x0000) - not-present page
> [ 502.716546] PGD 103984067 P4D 103984067 PUD 17592b067 PMD 0
> [ 502.717252] Oops: 0000 [#1] SMP
> [ 502.720308] RIP: 0010:trace_note.isra.0+0x86/0x360
> [ 502.732872] Call Trace:
> [ 502.733193] __blk_add_trace.cold+0x137/0x1a3
> [ 502.733734] blk_add_trace_rq+0x7b/0xd0
> [ 502.734207] blk_add_trace_rq_issue+0x54/0xa0
> [ 502.734755] blk_mq_start_request+0xde/0x1b0
> [ 502.735287] scsi_queue_rq+0x528/0x1140
> ...
> [ 502.742704] sg_new_write.isra.0+0x16e/0x3e0
> [ 502.747501] sg_ioctl+0x466/0x1100
>
> Reproduce method:
> ioctl(/dev/sda, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])
> ioctl(/dev/sda, BLKTRACESTART)
> ioctl(/dev/sdb, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])
> ioctl(/dev/sdb, BLKTRACESTART)
>
> echo 0 > /sys/block/sdb/trace/enable &
> // Add delay(mdelay/msleep) before kernel enters blk_trace_free()
>
> ioctl$SG_IO(/dev/sda, SG_IO, ...)
> // Enters trace_note_tsk() after blk_trace_free() returned
> // Use mdelay in rcu region rather than msleep(which may schedule out)
>
> Don't remove blk_trace by sysfs when blk_trace is at Blktrace_running
> state, just like function __blk_trace_remove() does. The state change
> process and blk_trace_remove_queue() are protected and by mutex lock
> 'q->debugfs_mutex', so the sequence of stopping blk_trace first and
> then removing it will be ensured.
>
> Fixes: c71a896154119f ("blktrace: add ftrace plugin")
> Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
> ---
> kernel/trace/blktrace.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index c221e4c3f625..7fe29bb9746f 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -1821,8 +1821,17 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
> }
> if (value)
> ret = blk_trace_setup_queue(q, bdev);
> - else
> - ret = blk_trace_remove_queue(q);
> + else {
> + /*
> + * Don't remove blk_trace under running state, in
> + * case triggering use-after-free in function
> + * __blk_add_trace().
> + */
> + if (bt->trace_state != Blktrace_running)
> + ret = blk_trace_remove_queue(q);
> + else
> + ret = -EBUSY;
> + }
> goto out_unlock_bdev;
> }
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] blktrace: Fix uaf in blk_trace access after removing by sysfs
2021-09-10 9:21 [PATCH] blktrace: Fix uaf in blk_trace access after removing by sysfs Zhihao Cheng
2021-09-22 1:15 ` Zhihao Cheng
@ 2021-09-22 5:21 ` Christoph Hellwig
2021-09-23 13:39 ` Zhihao Cheng
1 sibling, 1 reply; 4+ messages in thread
From: Christoph Hellwig @ 2021-09-22 5:21 UTC (permalink / raw)
To: Zhihao Cheng
Cc: axboe, rostedt, mingo, acme, linux-block, linux-kernel, yukuai3
On Fri, Sep 10, 2021 at 05:21:20PM +0800, Zhihao Cheng wrote:
> + else {
> + /*
> + * Don't remove blk_trace under running state, in
> + * case triggering use-after-free in function
> + * __blk_add_trace().
> + */
> + if (bt->trace_state != Blktrace_running)
> + ret = blk_trace_remove_queue(q);
> + else
> + ret = -EBUSY;
> + }
> goto out_unlock_bdev;
So who is going to eventually call blk_trace_free in this case?
Also Having the check in blk_trace_remove_queue would seem a little
cleaner.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] blktrace: Fix uaf in blk_trace access after removing by sysfs
2021-09-22 5:21 ` Christoph Hellwig
@ 2021-09-23 13:39 ` Zhihao Cheng
0 siblings, 0 replies; 4+ messages in thread
From: Zhihao Cheng @ 2021-09-23 13:39 UTC (permalink / raw)
To: Christoph Hellwig
Cc: axboe, rostedt, mingo, acme, linux-block, linux-kernel, yukuai3
在 2021/9/22 13:21, Christoph Hellwig 写道:
Hi Christoph,
> On Fri, Sep 10, 2021 at 05:21:20PM +0800, Zhihao Cheng wrote:
>> + else {
>> + /*
>> + * Don't remove blk_trace under running state, in
>> + * case triggering use-after-free in function
>> + * __blk_add_trace().
>> + */
>> + if (bt->trace_state != Blktrace_running)
>> + ret = blk_trace_remove_queue(q);
>> + else
>> + ret = -EBUSY;
>> + }
>> goto out_unlock_bdev;
> So who is going to eventually call blk_trace_free in this case?
Agree. How about removing blk_trace from running_list and stopping it
before calling blk_trace_free()?
>
> Also Having the check in blk_trace_remove_queue would seem a little
> cleaner.
Oh right, will move the check in v2.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-09-23 13:39 UTC | newest]
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2021-09-10 9:21 [PATCH] blktrace: Fix uaf in blk_trace access after removing by sysfs Zhihao Cheng
2021-09-22 1:15 ` Zhihao Cheng
2021-09-22 5:21 ` Christoph Hellwig
2021-09-23 13:39 ` Zhihao Cheng
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