fs/namespace.c:3039: warning: Function parameter or member 'mp' not described in 'can_move_mount_beneath'

From: kernel test robot
Date: Wed Aug 30 2023 - 23:44:34 EST


tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head: ef2a0b7cdbc5b84f7b3f6573b7687e72bede0964
commit: 6ac392815628f317fcfdca1a39df00b9cc4ebc8b fs: allow to mount beneath top mount
date: 3 months ago
config: i386-allnoconfig (https://download.01.org/0day-ci/archive/20230831/202308311134.I4o8LaaZ-lkp@xxxxxxxxx/config)
compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230831/202308311134.I4o8LaaZ-lkp@xxxxxxxxx/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@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202308311134.I4o8LaaZ-lkp@xxxxxxxxx/

All warnings (new ones prefixed by >>):

>> fs/namespace.c:3039: warning: Function parameter or member 'mp' not described in 'can_move_mount_beneath'


vim +3039 fs/namespace.c

3015
3016 /**
3017 * can_move_mount_beneath - check that we can mount beneath the top mount
3018 * @from: mount to mount beneath
3019 * @to: mount under which to mount
3020 *
3021 * - Make sure that @to->dentry is actually the root of a mount under
3022 * which we can mount another mount.
3023 * - Make sure that nothing can be mounted beneath the caller's current
3024 * root or the rootfs of the namespace.
3025 * - Make sure that the caller can unmount the topmost mount ensuring
3026 * that the caller could reveal the underlying mountpoint.
3027 * - Ensure that nothing has been mounted on top of @from before we
3028 * grabbed @namespace_sem to avoid creating pointless shadow mounts.
3029 * - Prevent mounting beneath a mount if the propagation relationship
3030 * between the source mount, parent mount, and top mount would lead to
3031 * nonsensical mount trees.
3032 *
3033 * Context: This function expects namespace_lock() to be held.
3034 * Return: On success 0, and on error a negative error code is returned.
3035 */
3036 static int can_move_mount_beneath(const struct path *from,
3037 const struct path *to,
3038 const struct mountpoint *mp)
> 3039 {
3040 struct mount *mnt_from = real_mount(from->mnt),
3041 *mnt_to = real_mount(to->mnt),
3042 *parent_mnt_to = mnt_to->mnt_parent;
3043
3044 if (!mnt_has_parent(mnt_to))
3045 return -EINVAL;
3046
3047 if (!path_mounted(to))
3048 return -EINVAL;
3049
3050 if (IS_MNT_LOCKED(mnt_to))
3051 return -EINVAL;
3052
3053 /* Avoid creating shadow mounts during mount propagation. */
3054 if (path_overmounted(from))
3055 return -EINVAL;
3056
3057 /*
3058 * Mounting beneath the rootfs only makes sense when the
3059 * semantics of pivot_root(".", ".") are used.
3060 */
3061 if (&mnt_to->mnt == current->fs->root.mnt)
3062 return -EINVAL;
3063 if (parent_mnt_to == current->nsproxy->mnt_ns->root)
3064 return -EINVAL;
3065
3066 for (struct mount *p = mnt_from; mnt_has_parent(p); p = p->mnt_parent)
3067 if (p == mnt_to)
3068 return -EINVAL;
3069
3070 /*
3071 * If the parent mount propagates to the child mount this would
3072 * mean mounting @mnt_from on @mnt_to->mnt_parent and then
3073 * propagating a copy @c of @mnt_from on top of @mnt_to. This
3074 * defeats the whole purpose of mounting beneath another mount.
3075 */
3076 if (propagation_would_overmount(parent_mnt_to, mnt_to, mp))
3077 return -EINVAL;
3078
3079 /*
3080 * If @mnt_to->mnt_parent propagates to @mnt_from this would
3081 * mean propagating a copy @c of @mnt_from on top of @mnt_from.
3082 * Afterwards @mnt_from would be mounted on top of
3083 * @mnt_to->mnt_parent and @mnt_to would be unmounted from
3084 * @mnt->mnt_parent and remounted on @mnt_from. But since @c is
3085 * already mounted on @mnt_from, @mnt_to would ultimately be
3086 * remounted on top of @c. Afterwards, @mnt_from would be
3087 * covered by a copy @c of @mnt_from and @c would be covered by
3088 * @mnt_from itself. This defeats the whole purpose of mounting
3089 * @mnt_from beneath @mnt_to.
3090 */
3091 if (propagation_would_overmount(parent_mnt_to, mnt_from, mp))
3092 return -EINVAL;
3093
3094 return 0;
3095 }
3096

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