[linux-next:master 4018/13846] drivers/net/tun.c:2375:24: sparse: sparse: cast to non-scalar

[linux-next:master 4018/13846] drivers/net/tun.c:2375:24: sparse: sparse: cast to non-scalar

[kernel test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   6b8c8af514d739d0335f5579b585e02babe8a727
commit: 23dad2d088dfc82cae1f5a936f8ff7ffebb38dd9 [4018/13846] tun: no longer rely on RTNL in tun_fill_info()
config: alpha-randconfig-r134-20260810 (https://download.01.org/0day-ci/archive/20260810/202608101002.AO7X3ZCH-lkp@intel.com/config)
compiler: alpha-linux-gcc (GCC) 14.3.0
sparse: v0.6.5-rc1
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260810/202608101002.AO7X3ZCH-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202608101002.AO7X3ZCH-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> drivers/net/tun.c:2375:24: sparse: sparse: cast to non-scalar
>> drivers/net/tun.c:2375:24: sparse: sparse: cast from non-scalar
   drivers/net/tun.c:2376:24: sparse: sparse: cast to non-scalar
   drivers/net/tun.c:2376:24: sparse: sparse: cast from non-scalar

vim +2375 drivers/net/tun.c

  2370	
  2371	static int tun_fill_info(struct sk_buff *skb, const struct net_device *dev)
  2372	{
  2373		const struct tun_struct *tun = netdev_priv(dev);
  2374		unsigned int flags = READ_ONCE(tun->flags);
> 2375		kuid_t owner = READ_ONCE(tun->owner);
  2376		kgid_t group = READ_ONCE(tun->group);
  2377	
  2378		if (nla_put_u8(skb, IFLA_TUN_TYPE, flags & TUN_TYPE_MASK))
  2379			goto nla_put_failure;
  2380		if (uid_valid(owner) &&
  2381		    nla_put_u32(skb, IFLA_TUN_OWNER,
  2382				from_kuid_munged(current_user_ns(), owner)))
  2383			goto nla_put_failure;
  2384		if (gid_valid(group) &&
  2385		    nla_put_u32(skb, IFLA_TUN_GROUP,
  2386				from_kgid_munged(current_user_ns(), group)))
  2387			goto nla_put_failure;
  2388		if (nla_put_u8(skb, IFLA_TUN_PI, !(flags & IFF_NO_PI)))
  2389			goto nla_put_failure;
  2390		if (nla_put_u8(skb, IFLA_TUN_VNET_HDR, !!(flags & IFF_VNET_HDR)))
  2391			goto nla_put_failure;
  2392		if (nla_put_u8(skb, IFLA_TUN_PERSIST, !!(flags & IFF_PERSIST)))
  2393			goto nla_put_failure;
  2394		if (nla_put_u8(skb, IFLA_TUN_MULTI_QUEUE,
  2395			       !!(flags & IFF_MULTI_QUEUE)))
  2396			goto nla_put_failure;
  2397		if (flags & IFF_MULTI_QUEUE) {
  2398			if (nla_put_u32(skb, IFLA_TUN_NUM_QUEUES,
  2399					READ_ONCE(tun->numqueues)))
  2400				goto nla_put_failure;
  2401			if (nla_put_u32(skb, IFLA_TUN_NUM_DISABLED_QUEUES,
  2402					READ_ONCE(tun->numdisabled)))
  2403				goto nla_put_failure;
  2404		}
  2405	
  2406		return 0;
  2407	
  2408	nla_put_failure:
  2409		return -EMSGSIZE;
  2410	}
  2411	

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [linux-next:master 4018/13846] drivers/net/tun.c:2375:24: sparse: sparse: cast to non-scalar

[Willem de Bruijn]

On Sun, Aug 9, 2026 at 11:33 PM kernel test robot <lkp@intel.com> wrote:
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   6b8c8af514d739d0335f5579b585e02babe8a727
> commit: 23dad2d088dfc82cae1f5a936f8ff7ffebb38dd9 [4018/13846] tun: no longer rely on RTNL in tun_fill_info()
> config: alpha-randconfig-r134-20260810 (https://download.01.org/0day-ci/archive/20260810/202608101002.AO7X3ZCH-lkp@intel.com/config)
> compiler: alpha-linux-gcc (GCC) 14.3.0
> sparse: v0.6.5-rc1
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260810/202608101002.AO7X3ZCH-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202608101002.AO7X3ZCH-lkp@intel.com/
>
> sparse warnings: (new ones prefixed by >>)
> >> drivers/net/tun.c:2375:24: sparse: sparse: cast to non-scalar
> >> drivers/net/tun.c:2375:24: sparse: sparse: cast from non-scalar
>    drivers/net/tun.c:2376:24: sparse: sparse: cast to non-scalar
>    drivers/net/tun.c:2376:24: sparse: sparse: cast from non-scalar
>
> vim +2375 drivers/net/tun.c
>
>   2370
>   2371  static int tun_fill_info(struct sk_buff *skb, const struct net_device *dev)
>   2372  {
>   2373          const struct tun_struct *tun = netdev_priv(dev);
>   2374          unsigned int flags = READ_ONCE(tun->flags);
> > 2375          kuid_t owner = READ_ONCE(tun->owner);

I guess this would need to be owner.val and group.val to silence this
warning. Both from and to arguments.

That approach would not improve readability.

Types:

typedef struct {
        uid_t val;
} kuid_t;

typedef struct {
        gid_t val;
} kgid_t;

Whatever we choose to do (if anything), probably also applies to sk_uid:

static inline kuid_t sk_uid(const struct sock *sk)
{
        /* Paired with WRITE_ONCE() in sockfs_setattr() */
        return READ_ONCE(sk->sk_uid);
}

Another helper, make_kuid, uses a KUIDT_INIT wrapper to cast to the struct type.