linux-kernel - Re: [PATCH] block: floppy: fix uninitialized use of outparam in fd_locked

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Message-ID: <1d255c16-46fb-413d-b25a-0f1fea682a33@linux.com>
Date: Sat, 12 Jul 2025 23:16:38 +0400
From: Denis Efremov <efremov@...ux.com>
To: Purva Yeshi <purvayeshi550@...il.com>, axboe@...nel.dk
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: floppy: fix uninitialized use of outparam in
 fd_locked_ioctl

Hello,

Thank you for the report!

On 06/07/2025 11:22, Purva Yeshi wrote:
> Fix Smatch-detected error:
> drivers/block/floppy.c:3569 fd_locked_ioctl() error:
> uninitialized symbol 'outparam'.
> 

This a false-positive diagnostic. Smatch doesn't see the dependency
between FDGET... commands and _IOC_READ.

> Use the outparam pointer only after it is explicitly initialized.
> Previously, fd_copyout() was called unconditionally after the switch-case
> statement, assuming outparam would always be set when _IOC_READ was active.

        if (_IOC_DIR(cmd) & _IOC_READ)
                return fd_copyout((void __user *)param, outparam, size);

and all FDGET... macro are defined as _IOR(...).

> However, not all paths ensured this, which led to potential use of an
> uninitialized pointer.

Not all paths, but commands that fall under _IOC_READ condition. 

> 
> Move fd_copyout() calls directly into the relevant case blocks immediately
> after outparam is set. This ensures it is only called when safe and
> applicable.

If you want to suppress this "error" you can just initialize outparam
to NULL.

> 
> Signed-off-by: Purva Yeshi <purvayeshi550@...il.com>
> ---
>  drivers/block/floppy.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
> index e97432032f01..34ef756bb3b7 100644
> --- a/drivers/block/floppy.c
> +++ b/drivers/block/floppy.c
> @@ -3482,6 +3482,7 @@ static int fd_locked_ioctl(struct block_device *bdev, blk_mode_t mode,
>  		memcpy(&inparam.g, outparam,
>  				offsetof(struct floppy_struct, name));
>  		outparam = &inparam.g;
> +		return fd_copyout((void __user *)param, outparam, size);
>  		break;
>  	case FDMSGON:
>  		drive_params[drive].flags |= FTD_MSG;
> @@ -3515,6 +3516,7 @@ static int fd_locked_ioctl(struct block_device *bdev, blk_mode_t mode,
>  		return 0;
>  	case FDGETMAXERRS:
>  		outparam = &drive_params[drive].max_errors;
> +		return fd_copyout((void __user *)param, outparam, size);
>  		break;
>  	case FDSETMAXERRS:
>  		drive_params[drive].max_errors = inparam.max_errors;
> @@ -3522,6 +3524,7 @@ static int fd_locked_ioctl(struct block_device *bdev, blk_mode_t mode,
>  	case FDGETDRVTYP:
>  		outparam = drive_name(type, drive);
>  		SUPBOUND(size, strlen((const char *)outparam) + 1);
> +		return fd_copyout((void __user *)param, outparam, size);
>  		break;
>  	case FDSETDRVPRM:
>  		if (!valid_floppy_drive_params(inparam.dp.autodetect,
> @@ -3531,6 +3534,7 @@ static int fd_locked_ioctl(struct block_device *bdev, blk_mode_t mode,
>  		break;
>  	case FDGETDRVPRM:
>  		outparam = &drive_params[drive];
> +		return fd_copyout((void __user *)param, outparam, size);
>  		break;
>  	case FDPOLLDRVSTAT:
>  		if (lock_fdc(drive))
> @@ -3541,17 +3545,20 @@ static int fd_locked_ioctl(struct block_device *bdev, blk_mode_t mode,
>  		fallthrough;
>  	case FDGETDRVSTAT:
>  		outparam = &drive_state[drive];
> +		return fd_copyout((void __user *)param, outparam, size);
>  		break;
>  	case FDRESET:
>  		return user_reset_fdc(drive, (int)param, true);
>  	case FDGETFDCSTAT:
>  		outparam = &fdc_state[FDC(drive)];
> +		return fd_copyout((void __user *)param, outparam, size);
>  		break;
>  	case FDWERRORCLR:
>  		memset(&write_errors[drive], 0, sizeof(write_errors[drive]));
>  		return 0;
>  	case FDWERRORGET:
>  		outparam = &write_errors[drive];
> +		return fd_copyout((void __user *)param, outparam, size);
>  		break;
>  	case FDRAWCMD:
>  		return floppy_raw_cmd_ioctl(type, drive, cmd, (void __user *)param);
> @@ -3565,9 +3572,6 @@ static int fd_locked_ioctl(struct block_device *bdev, blk_mode_t mode,
>  		return -EINVAL;
>  	}
>  
> -	if (_IOC_DIR(cmd) & _IOC_READ)
> -		return fd_copyout((void __user *)param, outparam, size);
> -
>  	return 0;
>  }
>  

Thanks,
Denis