Re: [PATCH] raid1: fix use-after-free for original bio in raid1_write_request()

[Coly Li]

On Fri, Mar 08, 2024 at 05:37:26PM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
> 
> r1_bio->bios[] is used to record new bios that will be issued to
> underlying disks, however, in raid1_write_request(), r1_bio->bios[]
> will set to the original bio temporarily. Meanwhile, if blocked rdev
> is set, free_r1bio() will be called causing that all r1_bio->bios[]
> to be freed:
> 
> raid1_write_request()
>  r1_bio = alloc_r1bio(mddev, bio); -> r1_bio->bios[] is NULL
>  for (i = 0;  i < disks; i++) -> for each rdev in conf
>   // first rdev is normal
>   r1_bio->bios[0] = bio; -> set to original bio
>   // second rdev is blocked
>   if (test_bit(Blocked, &rdev->flags))
>    break
> 
>  if (blocked_rdev)
>   free_r1bio()
>    put_all_bios()
>     bio_put(r1_bio->bios[0]) -> original bio is freed
> 
> Test scripts:
> 
> mdadm -CR /dev/md0 -l1 -n4 /dev/sd[abcd] --assume-clean
> fio -filename=/dev/md0 -ioengine=libaio -rw=write -bs=4k -numjobs=1 \
>     -iodepth=128 -name=test -direct=1
> echo blocked > /sys/block/md0/md/rd2/state
> 
> Test result:
> 
> BUG bio-264 (Not tainted): Object already free
> -----------------------------------------------------------------------------
> 
> Allocated in mempool_alloc_slab+0x24/0x50 age=1 cpu=1 pid=869
>  kmem_cache_alloc+0x324/0x480
>  mempool_alloc_slab+0x24/0x50
>  mempool_alloc+0x6e/0x220
>  bio_alloc_bioset+0x1af/0x4d0
>  blkdev_direct_IO+0x164/0x8a0
>  blkdev_write_iter+0x309/0x440
>  aio_write+0x139/0x2f0
>  io_submit_one+0x5ca/0xb70
>  __do_sys_io_submit+0x86/0x270
>  __x64_sys_io_submit+0x22/0x30
>  do_syscall_64+0xb1/0x210
>  entry_SYSCALL_64_after_hwframe+0x6c/0x74
> Freed in mempool_free_slab+0x1f/0x30 age=1 cpu=1 pid=869
>  kmem_cache_free+0x28c/0x550
>  mempool_free_slab+0x1f/0x30
>  mempool_free+0x40/0x100
>  bio_free+0x59/0x80
>  bio_put+0xf0/0x220
>  free_r1bio+0x74/0xb0
>  raid1_make_request+0xadf/0x1150
>  md_handle_request+0xc7/0x3b0
>  md_submit_bio+0x76/0x130
>  __submit_bio+0xd8/0x1d0
>  submit_bio_noacct_nocheck+0x1eb/0x5c0
>  submit_bio_noacct+0x169/0xd40
>  submit_bio+0xee/0x1d0
>  blkdev_direct_IO+0x322/0x8a0
>  blkdev_write_iter+0x309/0x440
>  aio_write+0x139/0x2f0
> 
> Since that bios for underlying disks are not allocated yet, fix this
> problem by using mempool_free() directly to free the r1_bio.
> 

Yes, the panic doesn't show up anymore with this patch.

Thanks for the fixup.


> Fixes: 992db13a4aee ("md/raid1: free the r1bio before waiting for blocked rdev")
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>

Reported-and-tested-by: Coly Li <colyli@xxxxxxx>


Coly Li

> ---
>  drivers/md/raid1.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index afca975ec7f3..fde8434c33df 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -1565,7 +1565,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
>  		for (j = 0; j < i; j++)
>  			if (r1_bio->bios[j])
>  				rdev_dec_pending(conf->mirrors[j].rdev, mddev);
> -		free_r1bio(r1_bio);
> +		mempool_free(r1_bio, &conf->r1bio_pool);
>  		allow_barrier(conf, bio->bi_iter.bi_sector);
>  
>  		if (bio->bi_opf & REQ_NOWAIT) {
> -- 
> 2.39.2
> 
>