Re: [PATCH v5 2/6] ocfs2: Switch to security_inode_init_security()

From: Mimi Zohar
Date: Tue Nov 29 2022 - 08:16:26 EST

On Thu, 2022-11-24 at 09:11 +0100, Roberto Sassu wrote:
> On Wed, 2022-11-23 at 12:46 -0500, Mimi Zohar wrote:
> > On Wed, 2022-11-23 at 10:51 +0100, Roberto Sassu wrote:
> > > From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > >
> > > In preparation for removing security_old_inode_init_security(), switch to
> > > security_inode_init_security().
> > >
> > > Extend the existing ocfs2_initxattrs() to take the
> > > ocfs2_security_xattr_info structure from fs_info, and populate the
> > > name/value/len triple with the first xattr provided by LSMs. Supporting
> > > multiple xattrs is not currently supported, as it requires non-trivial
> > > changes that can be done at a later time.
> >
> > ocfs2 already defines ocfs2_init_security_get() as a wrapper around
> > calling either security_old_inode_init_security() or
> > security_inode_init_security(). Based on "si" one or the other hook is
> > called. ocfs2_initxattrs is already defined.
> >
> > struct ocfs2_security_xattr_info si = {
> > .name = NULL,
> > .enable = 1,
> > };
> >
> > The main difference between calling security_old_inode_init_security or
> > security_inode_init_security() is whether or not security.evm is
> > calculated and written.
>
> Uhm, it seems unfortunately more complicated.
>
> Calling security_old_inode_init_security() allows filesystems to get
> the xattr, do some calculations (e.g. for reservation) and then write
> the xattr.
>
> The initxattrs() callback to be passed to
> security_inode_init_security() is meant to let filesystems provide a
> filesystem-specific way of writing the xattrs, just after LSMs provided
> them. This seems incompatible with the old behavior, as a filesystem
> might need to do the calculations in the middle before writing the
> xattrs.
>
> The initxattrs() callback, when security_old_inode_init_security() was
> used, is just a way of emulating the old behavior, i.e. returning the
> xattr to the caller.
>
> It should be possible, I guess, to handle more xattrs but if the code
> was designed to handle one, it would be better if the filesystem
> maintainers add support for it.

Hi Mark, Joel, Joseph,

Commit 9d8f13ba3f48 ("security: new security_inode_init_security API
adds function callback") introduced security_old_inode_init_security()
to support reiserfs and ocfs2 a long time ago. It was suppose to be a
temporary fix until they moved to the new
security_inode_init_security() hook. ocsf2 partially migrated to
security_inode_init_security(), but not completely.

security_old_inode_init_security() is finally going away. Instead of
migrating the remaining old usage to the new
security_inode_init_security() properly, this patch simulates the
existing usage.

Can we get some Reviewed-by, Tested-by tags or comments?

thanks,

Mimi

>
> > Perhaps it is time to remove the call to
> > security_old_inode_init_security() in ocfs2_init_security_get(). We
> > need to hear back from the ocfs2 community. Mark? Joel?
> >
> > As noted previously this change affects mknod and symlinks.
> >
> >
> > > As fs_info was not used before, ocfs2_initxattrs() can now handle the case
> > > of replicating the behavior of security_old_inode_init_security(), i.e.
> > > just obtaining the xattr, in addition to setting all xattrs provided by
> > > LSMs.
> > >
> > > Finally, modify the handling of the return value from
> > > ocfs2_init_security_get(). As security_inode_init_security() does not
> > > return -EOPNOTSUPP, remove this case and directly handle the error if the
> > > return value is not zero.
> > >
> > > However, the previous case of receiving -EOPNOTSUPP should be still
> > > taken into account, as security_inode_init_security() could return zero
> > > without setting xattrs and ocfs2 would consider it as if the xattr was set.
> > >
> > > Instead, if security_inode_init_security() returned zero, look at the xattr
> > > if it was set, and behave accordingly, i.e. set si->enable to zero to
> > > notify to the functions following ocfs2_init_security_get() that the xattr
> > > is not available (same as if security_old_inode_init_security() returned
> > > -EOPNOTSUPP).
> > >
> > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > > ---
> > > fs/ocfs2/namei.c | 18 ++++++------------
> > > fs/ocfs2/xattr.c | 30 ++++++++++++++++++++++++++----
> > > 2 files changed, 32 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
> > > index 05f32989bad6..55fba81cd2d1 100644
> > > --- a/fs/ocfs2/namei.c
> > > +++ b/fs/ocfs2/namei.c
> > > @@ -242,6 +242,7 @@ static int ocfs2_mknod(struct user_namespace *mnt_userns,
> > > int want_meta = 0;
> > > int xattr_credits = 0;
> > > struct ocfs2_security_xattr_info si = {
> > > + .name = NULL,
> > > .enable = 1,
> > > };
> > > int did_quota_inode = 0;
> > > @@ -315,12 +316,8 @@ static int ocfs2_mknod(struct user_namespace *mnt_userns,
> > > /* get security xattr */
> > > status = ocfs2_init_security_get(inode, dir, &dentry->d_name, &si);
> > > if (status) {
> > > - if (status == -EOPNOTSUPP)
> > > - si.enable = 0;
> > > - else {
> > > - mlog_errno(status);
> > > - goto leave;
> > > - }
> > > + mlog_errno(status);
> > > + goto leave;
> > > }
> > >
> > > /* calculate meta data/clusters for setting security and acl xattr */
> > > @@ -1805,6 +1802,7 @@ static int ocfs2_symlink(struct user_namespace *mnt_userns,
> > > int want_clusters = 0;
> > > int xattr_credits = 0;
> > > struct ocfs2_security_xattr_info si = {
> > > + .name = NULL,
> > > .enable = 1,
> > > };
> > > int did_quota = 0, did_quota_inode = 0;
> > > @@ -1875,12 +1873,8 @@ static int ocfs2_symlink(struct user_namespace *mnt_userns,
> > > /* get security xattr */
> > > status = ocfs2_init_security_get(inode, dir, &dentry->d_name, &si);
> > > if (status) {
> > > - if (status == -EOPNOTSUPP)
> > > - si.enable = 0;
> > > - else {
> > > - mlog_errno(status);
> > > - goto bail;
> > > - }
> > > + mlog_errno(status);
> > > + goto bail;
> > > }
> > >
> > > /* calculate meta data/clusters for setting security xattr */
> > > diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
> > > index 95d0611c5fc7..55699c573541 100644
> > > --- a/fs/ocfs2/xattr.c
> > > +++ b/fs/ocfs2/xattr.c
> > > @@ -7259,9 +7259,21 @@ static int ocfs2_xattr_security_set(const struct xattr_handler *handler,
> > > static int ocfs2_initxattrs(struct inode *inode, const struct xattr *xattr_array,
> > > void *fs_info)
> > > {
> > > + struct ocfs2_security_xattr_info *si = fs_info;
> > > const struct xattr *xattr;
> > > int err = 0;
> > >
> > > + if (si) {
> > > + si->value = kmemdup(xattr_array->value, xattr_array->value_len,
> > > + GFP_KERNEL);
> > > + if (!si->value)
> > > + return -ENOMEM;
> > > +
> > > + si->name = xattr_array->name;
> > > + si->value_len = xattr_array->value_len;
> > > + return 0;
> > > + }
> > > +
> > > for (xattr = xattr_array; xattr->name != NULL; xattr++) {
> > > err = ocfs2_xattr_set(inode, OCFS2_XATTR_INDEX_SECURITY,
> > > xattr->name, xattr->value,
> > > @@ -7277,13 +7289,23 @@ int ocfs2_init_security_get(struct inode *inode,
> > > const struct qstr *qstr,
> > > struct ocfs2_security_xattr_info *si)
> > > {
> > > + int ret;
> > > +
> > > /* check whether ocfs2 support feature xattr */
> > > if (!ocfs2_supports_xattr(OCFS2_SB(dir->i_sb)))
> > > return -EOPNOTSUPP;
> > > - if (si)
> > > - return security_old_inode_init_security(inode, dir, qstr,
> > > - &si->name, &si->value,
> > > - &si->value_len);
> > > + if (si) {
> > > + ret = security_inode_init_security(inode, dir, qstr,
> > > + &ocfs2_initxattrs, si);
> > > + /*
> > > + * security_inode_init_security() does not return -EOPNOTSUPP,
> > > + * we have to check the xattr ourselves.
> > > + */
> > > + if (!ret && !si->name)
> > > + si->enable = 0;
> > > +
> > > + return ret;
> > > + }
> > >
> > > return security_inode_init_security(inode, dir, qstr,
> > > &ocfs2_initxattrs, NULL);
>