linux-kernel - Re: [PATCH] ublk: prevent invalid access with DEBUG

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Message-ID: <CADUfDZqsFSsA4UNxmB=LQwqor+enD35bNVFgT2_gMt1_2uwOqA@mail.gmail.com>
Date: Wed, 26 Nov 2025 08:20:45 -0800
From: Caleb Sander Mateos <csander@...estorage.com>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Ali Utku Selen <ali.utku.selen@....com>, Ming Lei <ming.lei@...hat.com>, 
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] ublk: prevent invalid access with DEBUG

On Wed, Nov 26, 2025 at 4:48 AM Kevin Brodsky <kevin.brodsky@....com> wrote:
>
> ublk_ch_uring_cmd_local() may jump to the out label before
> initialising the io pointer. This will cause trouble if DEBUG is
> defined, because the pr_devel() call dereferences io. Clang reports:
>
> drivers/block/ublk_drv.c:2403:6: error: variable 'io' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>  2403 |         if (tag >= ub->dev_info.queue_depth)
>       |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/block/ublk_drv.c:2492:32: note: uninitialized use occurs here
>  2492 |                         __func__, cmd_op, tag, ret, io->flags);
>       |
>
> Fix this by initialising io to NULL and checking it before
> dereferencing it.
>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>

Looks like this could use a Fixes tag:
Fixes: 71f28f3136af ("ublk_drv: add io_uring based userspace block driver")

Other than that,
Reviewed-by: Caleb Sander Mateos <csander@...estorage.com>

> ---
> Cc: Ali Utku Selen <ali.utku.selen@....com>
> Cc: Ming Lei <ming.lei@...hat.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> ---
>  drivers/block/ublk_drv.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 0c74a41a6753..359564c40cb5 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -2367,7 +2367,7 @@ static int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd,
>         u16 buf_idx = UBLK_INVALID_BUF_IDX;
>         struct ublk_device *ub = cmd->file->private_data;
>         struct ublk_queue *ubq;
> -       struct ublk_io *io;
> +       struct ublk_io *io = NULL;
>         u32 cmd_op = cmd->cmd_op;
>         u16 q_id = READ_ONCE(ub_src->q_id);
>         u16 tag = READ_ONCE(ub_src->tag);
> @@ -2488,7 +2488,7 @@ static int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd,
>
>   out:
>         pr_devel("%s: complete: cmd op %d, tag %d ret %x io_flags %x\n",
> -                       __func__, cmd_op, tag, ret, io->flags);
> +                       __func__, cmd_op, tag, ret, io ? io->flags : 0);
>         return ret;
>  }
>
>
> base-commit: ac3fd01e4c1efce8f2c054cdeb2ddd2fc0fb150d
> --
> 2.51.2
>
>