linux-kernel - Re: [PATCH] mtd: ubi: eba.c: fix return value overwrite issue in try_write_vid_and

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Date:   Mon, 20 Mar 2023 10:44:51 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     Wang YanQing <udknight@...il.com>, <miquel.raynal@...tlin.com>,
        <bbrezillon@...nel.org>, <richard@....at>, <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mtd: ubi: eba.c: fix return value overwrite issue in
 try_write_vid_and_data()

Good catch. Maybe many of history happened unconsistent ubifs images 
have related to this point. One small nit below.

> The commit 2d78aee426d8 ("UBI: simplify LEB write and atomic LEB change code")
> adds helper function, try_write_vid_and_data(), to simplify the code, but this
> helper function has bug, it will return 0 (success) when ubi_io_write_vid_hdr()
> or the ubi_io_write_data() return error number (-EIO, etc), because the return
> value of ubi_wl_put_peb() will overwrite the original return value.
> 
> This issue will cause unexpected data loss issue, because the caller of this
> function and UBIFS willn't know the data is lost.
> 
> Fixes: 2d78aee426d8 ("UBI: simplify LEB write and atomic LEB change code")
> 
> Signed-off-by: Wang YanQing <udknight@...il.com>
> ---
>   drivers/mtd/ubi/eba.c | 15 +++++++++++----
>   1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/ubi/eba.c b/drivers/mtd/ubi/eba.c
> index 09c408c..4e32b25 100644
> --- a/drivers/mtd/ubi/eba.c
> +++ b/drivers/mtd/ubi/eba.c
> @@ -981,10 +981,17 @@ static int try_write_vid_and_data(struct ubi_volume *vol, int lnum,
>   out_put:
>   	up_read(&ubi->fm_eba_sem);
>   
> -	if (err && pnum >= 0)
> -		err = ubi_wl_put_peb(ubi, vol_id, lnum, pnum, 1);
> -	else if (!err && opnum >= 0)
> -		err = ubi_wl_put_peb(ubi, vol_id, lnum, opnum, 0);
> +	if (err && pnum >= 0) {
> +		if (ubi_wl_put_peb(ubi, vol_id, lnum, pnum, 1) != 0) {

Could we also add error code returned from ubi_wl_put_peb() in warning 
message? Same with next ubifs_warn.
> +			ubi_warn(ubi, "failed to return physical eraseblock %d",
> +				 pnum);
> +		}
> +	} else if (!err && opnum >= 0) {
> +		if (ubi_wl_put_peb(ubi, vol_id, lnum, opnum, 0) != 0) {
> +			ubi_warn(ubi, "failed to return physical eraseblock %d",
> +				 opnum);
> +		}
> +	}
>   
>   	return err;
>   }
>