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ovl: handle idmapped mounts in ovl_getattr()

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ovl_getattr() fetches attributes from the real (upper or lower) path
via vfs_getattr(), so the returned stat->uid/stat->gid are already
mapped through the real layer idmap but not through the overlay mount
idmap.  Unlike the generic path, the VFS does not re-apply the
accessing mount's idmap after ->getattr returns - generic_fillattr()
does it, but overlayfs bypasses it - so overlayfs has to do it itself.

Map stat->uid/stat->gid through the overlay mount idmap before
returning, mirroring generic_fillattr().  The owner reported through an
idmapped overlay mount is thus the overlay-final id translated by the
mount idmap.

No functional change until FS_ALLOW_IDMAP is set on ovl_fs_type; until
then make_vfsuid()/make_vfsgid() are the identity for &nop_mnt_idmap.

Link: https://patch.msgid.link/20260615-work-idmapped-overlayfs-v1-4-7381632aa402@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Christian Brauner
2026-06-15 15:19:53 +02:00
parent 10a16f5b91
commit 22b27d403d
1 changed files with 8 additions and 0 deletions
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8
fs/overlayfs/inode.c
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@@ -180,6 +180,8 @@ int ovl_getattr(struct mnt_idmap *idmap, const struct path *path,
int fsid = 0;
int err;
bool metacopy_blocks = false;
vfsuid_t vfsuid;
vfsgid_t vfsgid;
metacopy_blocks = ovl_is_metacopy_dentry(dentry);
@@ -292,6 +294,12 @@ int ovl_getattr(struct mnt_idmap *idmap, const struct path *path,
if (!is_dir && ovl_test_flag(OVL_INDEX, d_inode(dentry)))
stat->nlink = dentry->d_inode->i_nlink;
/* Map ownership of the real inode through the overlay mount idmap. */
vfsuid = make_vfsuid(idmap, i_user_ns(inode), stat->uid);
vfsgid = make_vfsgid(idmap, i_user_ns(inode), stat->gid);
stat->uid = vfsuid_into_kuid(vfsuid);
stat->gid = vfsgid_into_kgid(vfsgid);
return err;
}