fs: add copy_mount_setattr() helper

Split out copy_mount_setattr() from mount_setattr() so we can use it in
later patches.

Link: https://lore.kernel.org/r/20250128-work-mnt_idmap-update-v2-v1-2-c25feb0d2eb3@kernel.org
Reviewed-by: "Seth Forshee (DigitalOcean)" <sforshee@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index 7604cdacba20b2d84b7b063371bd98708e91cc73..d2ef1d69839bec308648dd1133ba8fb7240043cd 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -4814,7 +4814,7 @@ out:
 }
 
 static int build_mount_idmapped(const struct mount_attr *attr, size_t usize,
-                               struct mount_kattr *kattr, unsigned int flags)
+                               struct mount_kattr *kattr)
 {
        struct ns_common *ns;
        struct user_namespace *mnt_userns;
@@ -4865,22 +4865,8 @@ static int build_mount_idmapped(const struct mount_attr *attr, size_t usize,
 }
 
 static int build_mount_kattr(const struct mount_attr *attr, size_t usize,
-                            struct mount_kattr *kattr, unsigned int flags)
+                            struct mount_kattr *kattr)
 {
-       unsigned int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
-
-       if (flags & AT_NO_AUTOMOUNT)
-               lookup_flags &= ~LOOKUP_AUTOMOUNT;
-       if (flags & AT_SYMLINK_NOFOLLOW)
-               lookup_flags &= ~LOOKUP_FOLLOW;
-       if (flags & AT_EMPTY_PATH)
-               lookup_flags |= LOOKUP_EMPTY;
-
-       *kattr = (struct mount_kattr) {
-               .lookup_flags   = lookup_flags,
-               .recurse        = !!(flags & AT_RECURSIVE),
-       };
-
        if (attr->propagation & ~MOUNT_SETATTR_PROPAGATION_FLAGS)
                return -EINVAL;
        if (hweight32(attr->propagation & MOUNT_SETATTR_PROPAGATION_FLAGS) > 1)
@@ -4928,7 +4914,7 @@ static int build_mount_kattr(const struct mount_attr *attr, size_t usize,
                        return -EINVAL;
        }
 
-       return build_mount_idmapped(attr, usize, kattr, flags);
+       return build_mount_idmapped(attr, usize, kattr);
 }
 
 static void finish_mount_kattr(struct mount_kattr *kattr)
@@ -4940,23 +4926,14 @@ static void finish_mount_kattr(struct mount_kattr *kattr)
                mnt_idmap_put(kattr->mnt_idmap);
 }
 
-SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path,
-               unsigned int, flags, struct mount_attr __user *, uattr,
-               size_t, usize)
+static int copy_mount_setattr(struct mount_attr __user *uattr, size_t usize,
+                             struct mount_kattr *kattr)
 {
-       int err;
-       struct path target;
+       int ret;
        struct mount_attr attr;
-       struct mount_kattr kattr;
 
        BUILD_BUG_ON(sizeof(struct mount_attr) != MOUNT_ATTR_SIZE_VER0);
 
-       if (flags & ~(AT_EMPTY_PATH |
-                     AT_RECURSIVE |
-                     AT_SYMLINK_NOFOLLOW |
-                     AT_NO_AUTOMOUNT))
-               return -EINVAL;
-
        if (unlikely(usize > PAGE_SIZE))
                return -E2BIG;
        if (unlikely(usize < MOUNT_ATTR_SIZE_VER0))
@@ -4965,9 +4942,9 @@ SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path,
        if (!may_mount())
                return -EPERM;
 
-       err = copy_struct_from_user(&attr, sizeof(attr), uattr, usize);
-       if (err)
-               return err;
+       ret = copy_struct_from_user(&attr, sizeof(attr), uattr, usize);
+       if (ret)
+               return ret;
 
        /* Don't bother walking through the mounts if this is a nop. */
        if (attr.attr_set == 0 &&
@@ -4975,7 +4952,37 @@ SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path,
            attr.propagation == 0)
                return 0;
 
-       err = build_mount_kattr(&attr, usize, &kattr, flags);
+       return build_mount_kattr(&attr, usize, kattr);
+}
+
+SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path,
+               unsigned int, flags, struct mount_attr __user *, uattr,
+               size_t, usize)
+{
+       int err;
+       struct path target;
+       struct mount_kattr kattr;
+       unsigned int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
+
+       if (flags & ~(AT_EMPTY_PATH |
+                     AT_RECURSIVE |
+                     AT_SYMLINK_NOFOLLOW |
+                     AT_NO_AUTOMOUNT))
+               return -EINVAL;
+
+       if (flags & AT_NO_AUTOMOUNT)
+               lookup_flags &= ~LOOKUP_AUTOMOUNT;
+       if (flags & AT_SYMLINK_NOFOLLOW)
+               lookup_flags &= ~LOOKUP_FOLLOW;
+       if (flags & AT_EMPTY_PATH)
+               lookup_flags |= LOOKUP_EMPTY;
+
+       kattr = (struct mount_kattr) {
+               .lookup_flags   = lookup_flags,
+               .recurse        = !!(flags & AT_RECURSIVE),
+       };
+
+       err = copy_mount_setattr(uattr, usize, &kattr);
        if (err)
                return err;