On Tue, May 05, 2020 at 07:13:20PM +0300, Amir Goldstein wrote:
> > The patch cbe7fba8edfc: "ovl: make sure that real fid is 32bit
> > aligned in memory" from Nov 15, 2019, leads to the following static
> > checker warning:
> >
> > fs/overlayfs/export.c:791 ovl_fid_to_fh()
> > warn: check that subtract can't underflow
> >
> > fs/overlayfs/export.c
> > 775 static struct ovl_fh *ovl_fid_to_fh(struct fid *fid, int buflen, int fh_type)
> > 776 {
> > 777 struct ovl_fh *fh;
> > 778
> > 779 /* If on-wire inner fid is aligned - nothing to do */
> > 780 if (fh_type == OVL_FILEID_V1)
> > 781 return (struct ovl_fh *)fid;
> > 782
> > 783 if (fh_type != OVL_FILEID_V0)
> > 784 return ERR_PTR(-EINVAL);
> > 785
> > 786 fh = kzalloc(buflen, GFP_KERNEL);
>
> Doesn't Smatch warn on possible kmalloc(0)?
> That can't be good. Right?
No, no. Allocating zero bytes is a useful feature.
size = 0;
buf = kzalloc(size, GFP_KERNEL);
for (i = 0; i < size; i++)
buf[i] = 42;
memcpy(dest, buf, size);
copy_to_user(p, dest, size);
That all works. Neat, huh?
regards,
dan carpenter
