On 9/23/21 7:49 AM, Zhihao Cheng wrote: > 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) > > Remove blk_trace from running_list before calling blk_trace_free() by > sysfs if blk_trace is at Blktrace_running state. Applied, thanks. -- Jens Axboe
