linux-kernel - Re: [PATCH] scsi: fix uninitialized pointers with free attr

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Message-ID: <f6592ccc-155d-48ba-bac6-6e2b719a5c3e@suswa.mountain>
Date: Wed, 5 Nov 2025 17:46:31 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: James Bottomley <James.Bottomley@...senpartnership.com>
Cc: Ally Heev <allyheev@...il.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: fix uninitialized pointers with free attr

On Wed, Nov 05, 2025 at 09:21:45AM -0500, James Bottomley wrote:
> On Wed, 2025-11-05 at 19:44 +0530, Ally Heev wrote:
> > Uninitialized pointers with `__free` attribute can cause undefined
> > behaviour as the memory assigned(randomly) to the pointer is freed
> > automatically when the pointer goes out of scope
> > 
> > scsi doesn't have any bugs related to this as of now, but
> > it is better to initialize and assign pointers with `__free` attr
> > in one statement to ensure proper scope-based cleanup
> > 
> > Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> > Closes:
> > https://lore.kernel.org/all/aPiG_F5EBQUjZqsl@stanley.mountain/
> > Signed-off-by: Ally Heev <allyheev@...il.com>
> > ---
> >  drivers/scsi/scsi_debug.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> > index
> > b2ab97be5db3d43d5a5647968623b8db72448379..89b36d65926bdd15c0ae93a6bd2
> > ea968e25c0e74 100644
> > --- a/drivers/scsi/scsi_debug.c
> > +++ b/drivers/scsi/scsi_debug.c
> > @@ -2961,11 +2961,11 @@ static int resp_mode_sense(struct scsi_cmnd
> > *scp,
> >  	int target_dev_id;
> >  	int target = scp->device->id;
> >  	unsigned char *ap;
> > -	unsigned char *arr __free(kfree);
> >  	unsigned char *cmd = scp->cmnd;
> >  	bool dbd, llbaa, msense_6, is_disk, is_zbc, is_tape;
> >  
> > -	arr = kzalloc(SDEBUG_MAX_MSENSE_SZ, GFP_ATOMIC);
> > +	unsigned char *arr __free(kfree) =
> > kzalloc(SDEBUG_MAX_MSENSE_SZ, GFP_ATOMIC);
> > +
> 
> Moving variable assignments inside code makes it way harder to read. 
> Given that compilers will eventually detect if we do a return before
> initialization, can't you have smatch do the same rather than trying to
> force something like this?

This isn't a Smatch thing, it's a change to checkpatch.

(Smatch does work as you describe).

regards,
dan carpenter