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

Darrick J. Wong
2025-07-01T18:18:13Z

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@vger.kernel.org
> Cc: Paul Moore <paul@paul-moore.com>
>
> Acked-by: Paul Moore <paul@paul-moore.com>
> Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>

I wonder, were FS_IOC_FS[GS]ETXATTR already covered by the
security_file_ioctl hook? If so, will an out of date security policy
on a 6.17 kernel now fail to check the new file_[gs]etattr syscalls?

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@kernel.org>

--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
>
>