Messages in this thread | | | Subject | Re: [PATCH] blktrace: Fix uaf in blk_trace access after removing by sysfs | From | Zhihao Cheng <> | Date | Wed, 22 Sep 2021 09:15:28 +0800 |
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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; > } >
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