Re: [PATCH v6 2/6] lsm: introduce new hooks for setting/getting inode fsxattr

[Andrey Albershteyn]

On 2025-07-01 11:18:13, Darrick J. Wong wrote:
> On Mon, Jun 30, 2025 at 06:20:12PM +0200, Andrey Albershteyn wrote:
> > Introduce new hooks for setting and getting filesystem extended
> > attributes on inode (FS_IOC_FSGETXATTR).
> > 
> > Cc: selinux@xxxxxxxxxxxxxxx
> > Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
> > 
> > Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
> > Signed-off-by: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
> 
> I wonder, were FS_IOC_FS[GS]ETXATTR already covered by the
> security_file_ioctl hook? 

looks like

> If so, will an out of date security policy
> on a 6.17 kernel now fail to check the new file_[gs]etattr syscalls?

Yeah, probably, not sure if policies can have 'don't allow unknown'
but this is probably will need to be updated in the policy

> 
> Though AFAICT the future of managing these "extra" file attributes is
> the system call so it's probably appropriate to have an explicit
> callout to LSMs.
> 
> Acked-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
> 
> --D
> 
> > ---
> >  fs/file_attr.c                | 19 ++++++++++++++++---
> >  include/linux/lsm_hook_defs.h |  2 ++
> >  include/linux/security.h      | 16 ++++++++++++++++
> >  security/security.c           | 30 ++++++++++++++++++++++++++++++
> >  4 files changed, 64 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/file_attr.c b/fs/file_attr.c
> > index 2910b7047721..be62d97cc444 100644
> > --- a/fs/file_attr.c
> > +++ b/fs/file_attr.c
> > @@ -76,10 +76,15 @@ EXPORT_SYMBOL(fileattr_fill_flags);
> >  int vfs_fileattr_get(struct dentry *dentry, struct fileattr *fa)
> >  {
> >  	struct inode *inode = d_inode(dentry);
> > +	int error;
> >  
> >  	if (!inode->i_op->fileattr_get)
> >  		return -ENOIOCTLCMD;
> >  
> > +	error = security_inode_file_getattr(dentry, fa);
> > +	if (error)
> > +		return error;
> > +
> >  	return inode->i_op->fileattr_get(dentry, fa);
> >  }
> >  EXPORT_SYMBOL(vfs_fileattr_get);
> > @@ -242,12 +247,20 @@ int vfs_fileattr_set(struct mnt_idmap *idmap, struct dentry *dentry,
> >  		} else {
> >  			fa->flags |= old_ma.flags & ~FS_COMMON_FL;
> >  		}
> > +
> >  		err = fileattr_set_prepare(inode, &old_ma, fa);
> > -		if (!err)
> > -			err = inode->i_op->fileattr_set(idmap, dentry, fa);
> > +		if (err)
> > +			goto out;
> > +		err = security_inode_file_setattr(dentry, fa);
> > +		if (err)
> > +			goto out;
> > +		err = inode->i_op->fileattr_set(idmap, dentry, fa);
> > +		if (err)
> > +			goto out;
> >  	}
> > +
> > +out:
> >  	inode_unlock(inode);
> > -
> >  	return err;
> >  }
> >  EXPORT_SYMBOL(vfs_fileattr_set);
> > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> > index bf3bbac4e02a..9600a4350e79 100644
> > --- a/include/linux/lsm_hook_defs.h
> > +++ b/include/linux/lsm_hook_defs.h
> > @@ -157,6 +157,8 @@ LSM_HOOK(int, 0, inode_removexattr, struct mnt_idmap *idmap,
> >  	 struct dentry *dentry, const char *name)
> >  LSM_HOOK(void, LSM_RET_VOID, inode_post_removexattr, struct dentry *dentry,
> >  	 const char *name)
> > +LSM_HOOK(int, 0, inode_file_setattr, struct dentry *dentry, struct fileattr *fa)
> > +LSM_HOOK(int, 0, inode_file_getattr, struct dentry *dentry, struct fileattr *fa)
> >  LSM_HOOK(int, 0, inode_set_acl, struct mnt_idmap *idmap,
> >  	 struct dentry *dentry, const char *acl_name, struct posix_acl *kacl)
> >  LSM_HOOK(void, LSM_RET_VOID, inode_post_set_acl, struct dentry *dentry,
> > diff --git a/include/linux/security.h b/include/linux/security.h
> > index dba349629229..9ed0d0e0c81f 100644
> > --- a/include/linux/security.h
> > +++ b/include/linux/security.h
> > @@ -451,6 +451,10 @@ int security_inode_listxattr(struct dentry *dentry);
> >  int security_inode_removexattr(struct mnt_idmap *idmap,
> >  			       struct dentry *dentry, const char *name);
> >  void security_inode_post_removexattr(struct dentry *dentry, const char *name);
> > +int security_inode_file_setattr(struct dentry *dentry,
> > +			      struct fileattr *fa);
> > +int security_inode_file_getattr(struct dentry *dentry,
> > +			      struct fileattr *fa);
> >  int security_inode_need_killpriv(struct dentry *dentry);
> >  int security_inode_killpriv(struct mnt_idmap *idmap, struct dentry *dentry);
> >  int security_inode_getsecurity(struct mnt_idmap *idmap,
> > @@ -1052,6 +1056,18 @@ static inline void security_inode_post_removexattr(struct dentry *dentry,
> >  						   const char *name)
> >  { }
> >  
> > +static inline int security_inode_file_setattr(struct dentry *dentry,
> > +					      struct fileattr *fa)
> > +{
> > +	return 0;
> > +}
> > +
> > +static inline int security_inode_file_getattr(struct dentry *dentry,
> > +					      struct fileattr *fa)
> > +{
> > +	return 0;
> > +}
> > +
> >  static inline int security_inode_need_killpriv(struct dentry *dentry)
> >  {
> >  	return cap_inode_need_killpriv(dentry);
> > diff --git a/security/security.c b/security/security.c
> > index 596d41818577..711b4de40b8d 100644
> > --- a/security/security.c
> > +++ b/security/security.c
> > @@ -2622,6 +2622,36 @@ void security_inode_post_removexattr(struct dentry *dentry, const char *name)
> >  	call_void_hook(inode_post_removexattr, dentry, name);
> >  }
> >  
> > +/**
> > + * security_inode_file_setattr() - check if setting fsxattr is allowed
> > + * @dentry: file to set filesystem extended attributes on
> > + * @fa: extended attributes to set on the inode
> > + *
> > + * Called when file_setattr() syscall or FS_IOC_FSSETXATTR ioctl() is called on
> > + * inode
> > + *
> > + * Return: Returns 0 if permission is granted.
> > + */
> > +int security_inode_file_setattr(struct dentry *dentry, struct fileattr *fa)
> > +{
> > +	return call_int_hook(inode_file_setattr, dentry, fa);
> > +}
> > +
> > +/**
> > + * security_inode_file_getattr() - check if retrieving fsxattr is allowed
> > + * @dentry: file to retrieve filesystem extended attributes from
> > + * @fa: extended attributes to get
> > + *
> > + * Called when file_getattr() syscall or FS_IOC_FSGETXATTR ioctl() is called on
> > + * inode
> > + *
> > + * Return: Returns 0 if permission is granted.
> > + */
> > +int security_inode_file_getattr(struct dentry *dentry, struct fileattr *fa)
> > +{
> > +	return call_int_hook(inode_file_getattr, dentry, fa);
> > +}
> > +
> >  /**
> >   * security_inode_need_killpriv() - Check if security_inode_killpriv() required
> >   * @dentry: associated dentry
> > 
> > -- 
> > 2.47.2
> > 
> > 
> 

-- 
- Andrey