[PATCH] erofs: fix use-after-free of on-stack io[]

[Gao Xiang]

On Fri, Apr 01, 2022 at 02:33:01PM +0800, Hongyu Jin wrote:
> From: Hongyu Jin <hongyu.jin at unisoc.com>
> 
> The root cause is the race as follows(k5.4):
> Thread #1                               Thread #2(irq ctx)
> 
> z_erofs_submit_and_unzip()
>   struct z_erofs_vle_unzip_io io_A[]
>   submit bio A
>                                         z_erofs_vle_read_endio() // bio A
>                                         z_erofs_vle_unzip_kickoff()
>                                         spin_lock_irqsave()
>                                         atomic_add_return()
>   wait_event()
>   [end of function]
> z_erofs_submit_and_unzip() // bio B
>                                         wake_up_locked(io_A[]) // crash
>   struct z_erofs_vle_unzip_io io_B[]
>   submit bio B
>   wait_event()

Thanks, good catch!
Yet could you turn the race above into the current function names?

> 
> Backtrace in kernel5.4:
> [   10.129413] 8<--- cut here ---
> [   10.129422] Unable to handle kernel paging request at virtual address eb0454a4
> [   10.364157] CPU: 0 PID: 709 Comm: getprop Tainted: G        WC O      5.4.147-ab09225 #1
> [   11.556325] [<c01b33b8>] (__wake_up_common) from [<c01b3300>] (__wake_up_locked+0x40/0x48)
> [   11.565487] [<c01b3300>] (__wake_up_locked) from [<c044c8d0>] (z_erofs_vle_unzip_kickoff+0x6c/0xc0)
> [   11.575438] [<c044c8d0>] (z_erofs_vle_unzip_kickoff) from [<c044c854>] (z_erofs_vle_read_endio+0x16c/0x17c)
> [   11.586082] [<c044c854>] (z_erofs_vle_read_endio) from [<c06a80e8>] (clone_endio+0xb4/0x1d0)
> [   11.595428] [<c06a80e8>] (clone_endio) from [<c04a1280>] (blk_update_request+0x150/0x4dc)
> [   11.604516] [<c04a1280>] (blk_update_request) from [<c06dea28>] (mmc_blk_cqe_complete_rq+0x144/0x15c)
> [   11.614640] [<c06dea28>] (mmc_blk_cqe_complete_rq) from [<c04a5d90>] (blk_done_softirq+0xb0/0xcc)
> [   11.624419] [<c04a5d90>] (blk_done_softirq) from [<c010242c>] (__do_softirq+0x184/0x56c)
> [   11.633419] [<c010242c>] (__do_softirq) from [<c01051e8>] (irq_exit+0xd4/0x138)
> [   11.641640] [<c01051e8>] (irq_exit) from [<c010c314>] (__handle_domain_irq+0x94/0xd0)
> [   11.650381] [<c010c314>] (__handle_domain_irq) from [<c04fde70>] (gic_handle_irq+0x50/0xd4)
> [   11.659641] [<c04fde70>] (gic_handle_irq) from [<c0101b70>] (__irq_svc+0x70/0xb0)
> 
> Signed-off-by: Hongyu Jin <hongyu.jin at unisoc.com>
> ---
>  fs/erofs/zdata.c | 12 ++++--------
>  fs/erofs/zdata.h |  2 +-
>  2 files changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index 11c7a1aaebad..4c26faa817a3 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -782,12 +782,9 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
>  
>  	/* wake up the caller thread for sync decompression */
>  	if (sync) {
> -		unsigned long flags;
> -
> -		spin_lock_irqsave(&io->u.wait.lock, flags);
>  		if (!atomic_add_return(bios, &io->pending_bios))
> -			wake_up_locked(&io->u.wait);
> -		spin_unlock_irqrestore(&io->u.wait.lock, flags);
> +			complete(&io->u.done);
> +
>  		return;
>  	}
>  
> @@ -1207,7 +1204,7 @@ jobqueue_init(struct super_block *sb,
>  	} else {
>  fg_out:
>  		q = fgq;
> -		init_waitqueue_head(&fgq->u.wait);
> +		init_completion(&fgq->u.done);
>  		atomic_set(&fgq->pending_bios, 0);
>  	}
>  	q->sb = sb;
> @@ -1370,8 +1367,7 @@ static void z_erofs_runqueue(struct super_block *sb,
>  		return;
>  
>  	/* wait until all bios are completed */
> -	io_wait_event(io[JQ_SUBMIT].u.wait,
> -		      !atomic_read(&io[JQ_SUBMIT].pending_bios));
> +	wait_for_completion_io(&io[JQ_SUBMIT].u.done);

Thanks, good catch!

What if pending_bios is always 0 (nr_bios == 0), is it possible?

Thanks,
Gao Xiang