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

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Message-ID: <7dd94691-0b37-4855-be43-661f954275c8@gmail.com>
Date: Sun, 13 Jul 2025 11:22:35 +0530
From: Purva Yeshi <purvayeshi550@...il.com>
To: efremov@...ux.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

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@...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

Best regards,
Purva Yeshi

>