RE: [PATCH] qla4xxx: Return -ENOMEM on memory allocation failure

[Julia Lawall]

On Fri, 4 Jul 2014, Elliott, Robert (Server Storage) wrote:

> 
> 
> > -----Original Message-----
> > From: linux-scsi-owner@xxxxxxxxxxxxxxx [mailto:linux-scsi-
> > owner@xxxxxxxxxxxxxxx] On Behalf Of Himangi Saraogi
> > Sent: Friday, 04 July, 2014 1:28 PM
> > To: Vikas Chaudhary; iscsi-driver@xxxxxxxxxx; James E.J. Bottomley; linux-
> > scsi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > Cc: julia.lawall@xxxxxxx
> > Subject: [PATCH] qla4xxx: Return -ENOMEM on memory allocation failure
> > 
> > In this code, 0 is returned on memory allocation failure, even though
> > other failures return -ENOMEM or other similar values.
> > 
> > A simplified version of the Coccinelle semantic match that finds this
> > problem is as follows:
> > 
> > // <smpl>
> > @@
> > expression ret;
> > expression x,e1,e2,e3;
> > identifier alloc;
> > @@
> > 
> > ret = 0
> > ... when != ret = e1
> > *x = alloc(...)
> > ... when != ret = e2
> > if (x == NULL) { ... when != ret = e3
> >   return ret;
> > }
> > // </smpl>
> > 
> > Signed-off-by: Himangi Saraogi <himangi774@xxxxxxxxx>
> > Acked-by: Julia Lawall <julia.lawall@xxxxxxx>
> > ---
> >  drivers/scsi/qla4xxx/ql4_os.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/scsi/qla4xxx/ql4_os.c b/drivers/scsi/qla4xxx/ql4_os.c
> > index c5d9564..72ba671 100644
> > --- a/drivers/scsi/qla4xxx/ql4_os.c
> > +++ b/drivers/scsi/qla4xxx/ql4_os.c
> > @@ -1050,6 +1050,7 @@ static int qla4xxx_get_host_stats(struct Scsi_Host
> > *shost, char *buf, int len)
> >  	if (!ql_iscsi_stats) {
> >  		ql4_printk(KERN_ERR, ha,
> >  			   "Unable to allocate memory for iscsi stats\n");
> > +		ret = -ENOMEM;
> >  		goto exit_host_stats;
> >  	}
> > 
> 
> Also, the only caller of this function doesn't use the return 
> value - it's overwritten by another function call:
> 
> drivers/scsi/scsi_transport_iscsi.c:
>                 err = transport->get_host_stats(shost, buf, host_stats_size);
> 
>                 actual_size = nlmsg_total_size(sizeof(*ev) + host_stats_size);
>                 skb_trim(skbhost_stats, NLMSG_ALIGN(actual_size));
>                 nlhhost_stats->nlmsg_len = actual_size;
> 
>                 err = iscsi_multicast_skb(skbhost_stats, ISCSI_NL_GRP_ISCSID,
>                                           GFP_KERNEL);

Maybe that is intentional?  If get_host_stats fails, eg because of a lack 
of memory, the worst that will happen is that a region of the buffer will 
be 0.  If the loop is done again, there seems to be a risk of an infinite 
loop.

julia
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