On Fri, Dec 13, 2019 at 01:22:10PM +0100, Miklos Szeredi wrote:
> On Fri, Dec 13, 2019 at 11:38 AM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> >
> > Hello Amir Goldstein,
> >
> > This is a semi-automatic email about new static checker warnings.
> >
> > The patch cbe7fba8edfc: "ovl: make sure that real fid is 32bit
> > aligned in memory" from Nov 15, 2019, leads to the following Smatch
> > complaint:
> >
> > fs/overlayfs/copy_up.c:338 ovl_set_origin()
> > warn: variable dereferenced before check 'fh' (see line 337)
> >
> > fs/overlayfs/copy_up.c
> > 336 */
> > 337 err = ovl_check_setxattr(dentry, upper, OVL_XATTR_ORIGIN, fh->buf,
> > ^^^^^^^
> > The patch adds an unconditional dereference
>
> But in fact fh->buf is not a dereference:
>
> struct ovl_fh {
> u8 padding[3]; /* make sure fb.fid is 32bit aligned */
> union {
> struct ovl_fb fb;
> u8 buf[0];
> };
> } __packed;
>
> Subsequent code will also not dereference fh->buf, because the
> supplied size is zero.
Ah yes. Thanks. Smatch got confused because the array is inside a
union. Sorry.
regards,
dan carpenter
