Christian Brauner abfcf55d8b acl: handle idmapped mounts for idmapped filesystems ... Ensure that POSIX ACLs checking, getting, and setting works correctly for filesystems mountable with a filesystem idmapping ("fs_idmapping") that want to support idmapped mounts ("mnt_idmapping"). Note that no filesystems mountable with an fs_idmapping do yet support idmapped mounts. This is required infrastructure work to unblock this. As we explained in detail in [1] the fs_idmapping is irrelevant for getxattr() and setxattr() when mapping the ACL_{GROUP,USER} {g,u}ids stored in the uapi struct posix_acl_xattr_entry in posix_acl_fix_xattr_{from,to}_user(). But for acl_permission_check() and posix_acl_{g,s}etxattr_idmapped_mnt() the fs_idmapping matters. acl_permission_check(): During lookup POSIX ACLs are retrieved directly via i_op->get_acl() and are returned via the kernel internal struct posix_acl which contains e_{g,u}id members of type k{g,u}id_t that already take the fs_idmapping into acccount. For example, a POSIX ACL stored with u4 on the backing store is mapped to k10000004 in the fs_idmapping. The mnt_idmapping remaps the POSIX ACL to k20000004. In order to do that the fs_idmapping needs to be taken into account but that doesn't happen yet (Again, this is a counterfactual currently as fuse doesn't support idmapped mounts currently. It's just used as a convenient example.): fs_idmapping: u0:k10000000:r65536 mnt_idmapping: u0:v20000000:r65536 ACL_USER: k10000004 acl_permission_check() -> check_acl() -> get_acl() -> i_op->get_acl() == fuse_get_acl() -> posix_acl_from_xattr(u0:k10000000:r65536 /* fs_idmapping */, ...) { k10000004 = make_kuid(u0:k10000000:r65536 /* fs_idmapping */, u4 /* ACL_USER */); } -> posix_acl_permission() { -1 = make_vfsuid(u0:v20000000:r65536 /* mnt_idmapping */, &init_user_ns, k10000004); vfsuid_eq_kuid(-1, k10000004 /* caller_fsuid */) } In order to correctly map from the fs_idmapping into mnt_idmapping we require the relevant fs_idmaping to be passed: acl_permission_check() -> check_acl() -> get_acl() -> i_op->get_acl() == fuse_get_acl() -> posix_acl_from_xattr(u0:k10000000:r65536 /* fs_idmapping */, ...) { k10000004 = make_kuid(u0:k10000000:r65536 /* fs_idmapping */, u4 /* ACL_USER */); } -> posix_acl_permission() { v20000004 = make_vfsuid(u0:v20000000:r65536 /* mnt_idmapping */, u0:k10000000:r65536 /* fs_idmapping */, k10000004); vfsuid_eq_kuid(v20000004, k10000004 /* caller_fsuid */) } The initial_idmapping is only correct for the current situation because all filesystems that currently support idmapped mounts do not support being mounted with an fs_idmapping. Note that ovl_get_acl() is used to retrieve the POSIX ACLs from the relevant lower layer and the lower layer's mnt_idmapping needs to be taken into account and so does the fs_idmapping. See 0c5fd887d2 ("acl: move idmapped mount fixup into vfs_{g,s}etxattr()") for more details. For posix_acl_{g,s}etxattr_idmapped_mnt() it is not as obvious why the fs_idmapping matters as it is for acl_permission_check(). Especially because it doesn't matter for posix_acl_fix_xattr_{from,to}_user() (See [1] for more context.). Because posix_acl_{g,s}etxattr_idmapped_mnt() operate on the uapi struct posix_acl_xattr_entry which contains {g,u}id_t values and thus give the impression that the fs_idmapping is irrelevant as at this point appropriate {g,u}id_t values have seemlingly been generated. As we've stated multiple times this assumption is wrong and in fact the uapi struct posix_acl_xattr_entry is taking idmappings into account depending at what place it is operated on. posix_acl_getxattr_idmapped_mnt() When posix_acl_getxattr_idmapped_mnt() is called the values stored in the uapi struct posix_acl_xattr_entry are mapped according to the fs_idmapping. This happened when they were read from the backing store and then translated from struct posix_acl into the uapi struct posix_acl_xattr_entry during posix_acl_to_xattr(). In other words, the fs_idmapping matters as the values stored as {g,u}id_t in the uapi struct posix_acl_xattr_entry have been generated by it. So we need to take the fs_idmapping into account during make_vfsuid() in posix_acl_getxattr_idmapped_mnt(). posix_acl_setxattr_idmapped_mnt() When posix_acl_setxattr_idmapped_mnt() is called the values stored as {g,u}id_t in uapi struct posix_acl_xattr_entry are intended to be the values that ultimately get turned back into a k{g,u}id_t in posix_acl_from_xattr() (which turns the uapi struct posix_acl_xattr_entry into the kernel internal struct posix_acl). In other words, the fs_idmapping matters as the values stored as {g,u}id_t in the uapi struct posix_acl_xattr_entry are intended to be the values that will be undone in the fs_idmapping when writing to the backing store. So we need to take the fs_idmapping into account during from_vfsuid() in posix_acl_setxattr_idmapped_mnt(). Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1] Fixes: 0c5fd887d2 ("acl: move idmapped mount fixup into vfs_{g,s}etxattr()") Cc: Seth Forshee <sforshee@digitalocean.com> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> Reviewed-by: Seth Forshee <sforshee@digitalocean.com> Link: https://lore.kernel.org/r/20220816113514.43304-1-brauner@kernel.org		2022-08-17 11:23:31 +02:00
..
copy_up.c	Saner handling of "lseek should fail with ESPIPE" - gets rid of	2022-08-03 11:35:20 -07:00
dir.c
export.c	ovl: drop WARN_ON() dentry is NULL in ovl_encode_fh()	2022-07-28 15:00:57 +02:00
file.c	overlayfs update for 5.19	2022-05-30 11:19:16 -07:00
inode.c	acl: handle idmapped mounts for idmapped filesystems	2022-08-17 11:23:31 +02:00
Kconfig
Makefile
namei.c	ovl: fix spelling mistakes	2022-08-02 15:41:10 +02:00
overlayfs.h	overlayfs update for 6.0	2022-08-08 11:03:11 -07:00
ovl_entry.h	ovl: support idmapped layers	2022-04-28 16:31:12 +02:00
readdir.c
super.c	overlayfs update for 6.0	2022-08-08 11:03:11 -07:00
util.c