Re: [PATCH] block: floppy: fix uninitialized use of outparam in fd_locked_ioctl

[Purva Yeshi]

On 13/07/25 00:46, Denis Efremov wrote:
> 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.

Hi Denis,

Thank you for the detailed explanation and for reviewing patch.

> > 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(...).

Yes, I see it now.
All FDGET... commands that would enter the _IOC_READ block do initialize 
`outparam`, so it's guaranteed to be safe.

> > 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.

Got it.

> > 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.

I’ll update the patch to just initialize `outparam` to NULL to suppress 
the warning.

I’ll send a v2 patch soon.

> > Signed-off-by: Purva Yeshi <purvayeshi550@xxxxxxxxx>
> > ---
> >   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

Best regards,
Purva Yeshi

>