Re: [PATCH -next 0/2] lsm: Change inode_setattr() to take struct

[xiujianfeng]

sorry, I forgot to add the link to preview discussion:

https://lore.kernel.org/all/20220827111215.131442-1-xiujianfeng@xxxxxxxxxx/

On 2023/5/5 16:11, Xiu Jianfeng wrote:
> Hi,
> 
> I am working on adding xattr/attr support for landlock [1], so we can
> control fs accesses such as chmod, chown, uptimes, setxattr, etc.. inside
> landlock sandbox. the LSM hooks as following are invoved:
> 1.inode_setattr
> 2.inode_setxattr
> 3.inode_removexattr
> 4.inode_set_acl
> 5.inode_remove_acl
> which are controlled by LANDLOCK_ACCESS_FS_WRITE_METADATA.
> 
> and
> 1.inode_getattr
> 2.inode_get_acl
> 3.inode_getxattr
> 4.inode_listxattr
> which are controlled by LANDLOCK_ACCESS_FS_READ_METADATA
> 
> Some of these hooks only take struct dentry as a argument, However, for
> path-based LSMs such Landlock, Apparmor and Tomoyo, struct path instead
> of struct dentry required to make sense of attr/xattr accesses. So we
> need to refactor these hooks to take a struct path argument.
> 
> This patchset only refators inode_setattr hook as part of whole work.
> 
> Also, I have a problem about file_dentry() in __file_remove_privs() of the
> first patch, before changes in commit c1892c37769cf ("vfs: fix deadlock in
> file_remove_privs() on overlayfs"), it gets dentry and inode as belows:
> 
> struct dentry *dentry = file->f_path.dentry;
> struct inode *inode = d_inode(dentry);
> 
> That would be clear to change it to pass &file->f_path to
> __remove_privs()->notify_change()->inode_setattr().
> After that commit, it has been changed to:
> 
> struct dentry *dentry = file_dentry(file);
> struct inode *inode = file_inode(file);
> 
> If I understand correctly, the dentry from file_dentry() maybe the upper
> or the lower, it can be different from file->f_path.dentry. It can't just
> go back to use &file->f_path otherwise the bug will come back for
> overlayfs. So for such scenario, how to get a path from file if the file
> maybe or not from overlayfs, and which kind of overlayfs path is ok for
> Landlock?
> 
> Xiu Jianfeng (2):
>   fs: Change notify_change() to take struct path argument
>   lsm: Change inode_setattr hook to take struct path argument
> 
>  drivers/base/devtmpfs.c       |  5 +++--
>  fs/attr.c                     |  7 ++++---
>  fs/cachefiles/interface.c     |  4 ++--
>  fs/coredump.c                 |  2 +-
>  fs/ecryptfs/inode.c           | 18 +++++++++---------
>  fs/fat/file.c                 |  2 +-
>  fs/inode.c                    |  8 +++++---
>  fs/ksmbd/smb2pdu.c            |  6 +++---
>  fs/ksmbd/smbacl.c             |  2 +-
>  fs/namei.c                    |  2 +-
>  fs/nfsd/vfs.c                 | 12 ++++++++----
>  fs/open.c                     | 19 ++++++++++---------
>  fs/overlayfs/overlayfs.h      |  4 +++-
>  fs/utimes.c                   |  2 +-
>  include/linux/fs.h            |  4 ++--
>  include/linux/lsm_hook_defs.h |  2 +-
>  include/linux/security.h      |  4 ++--
>  security/security.c           | 10 +++++-----
>  security/selinux/hooks.c      |  3 ++-
>  security/smack/smack_lsm.c    |  5 +++--
>  20 files changed, 67 insertions(+), 54 deletions(-)
>