linux-kernel - Re: [PATCH] lsm: simplify security_inode_copy_up

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Message-ID: <CAHC9VhQ_f=YyFtxkMf0a8x-bRAi9Nzw-SdgEn8ndkDewydPzuA@mail.gmail.com>
Date: Wed, 30 Jul 2025 11:35:46 -0400
From: Paul Moore <paul@...l-moore.com>
To: "tianjia.zhang" <tianjia.zhang@...ux.alibaba.com>
Cc: Casey Schaufler <casey@...aufler-ca.com>, James Morris <jmorris@...ei.org>, 
	"Serge E. Hallyn" <serge@...lyn.com>, linux-security-module@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lsm: simplify security_inode_copy_up_xattr()

On Wed, Jul 30, 2025 at 5:26 AM tianjia.zhang
<tianjia.zhang@...ux.alibaba.com> wrote:
> On 7/29/25 11:09 PM, Paul Moore wrote:
> > On Tue, Jul 29, 2025 at 10:43 AM Casey Schaufler <casey@...aufler-ca.com> wrote:
> >> On 7/29/2025 2:09 AM, Tianjia Zhang wrote:
> >>> The implementation of function security_inode_copy_up_xattr can be
> >>> simplified to directly call call_int_hook().
> >>>
> >>> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> >>> ---
> >>>   security/security.c | 8 +-------
> >>>   1 file changed, 1 insertion(+), 7 deletions(-)
> >>>
> >>> diff --git a/security/security.c b/security/security.c
> >>> index 596d41818577..a5c2e5a8009f 100644
> >>> --- a/security/security.c
> >>> +++ b/security/security.c
> >>> @@ -2774,13 +2774,7 @@ EXPORT_SYMBOL(security_inode_copy_up);
> >>>    */
> >>>   int security_inode_copy_up_xattr(struct dentry *src, const char *name)
> >>>   {
> >>> -     int rc;
> >>> -
> >>> -     rc = call_int_hook(inode_copy_up_xattr, src, name);
> >>> -     if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
> >>> -             return rc;
> >>> -
> >>> -     return LSM_RET_DEFAULT(inode_copy_up_xattr);
> >>> +     return call_int_hook(inode_copy_up_xattr, src, name);
> >>
> >> Both the existing code and the proposed change are incorrect.
> >> If two LSMs supply the hook, and the first does not recognize
> >> the attribute, the second, which might recognize the attribute,
> >> will not be called. As SELinux and EVM both supply this hook
> >> there may be a real problem here.
> >
> > It appears that Smack also supplies a inode_copy_up_xattr() callback
> > via smack_inode_copy_up_xattr().
> >
> > Someone should double check this logic, but looking at it very
> > quickly, it would appear that LSM framework should run the individual
> > LSM callbacks in order so long as they return -EOPNOTSUPP, if they do
> > not return -EOPNOTSUPP, the return value should be returned to the
> > caller without executing any further callbacks.  As a default return
> > value, or if all of the LSM callbacks succeed with -EOPNOTSUPP, the
> > hook should return -EOPNOTSUPP.
> >
> > Tianjia Zhang, would you be able to develop and test a patch for this?
> >
>
> Yes, I will submit a new patch to try to fix this issue. Thanks for your
> suggestion.

Great, thank you.

-- 
paul-moore.com