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Date: Tue, 07 Nov 2023 18:45:25 +0100
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: Casey Schaufler <casey@...aufler-ca.com>, viro@...iv.linux.org.uk,
brauner@...nel.org, chuck.lever@...cle.com, jlayton@...nel.org,
neilb@...e.de, kolga@...app.com, Dai.Ngo@...cle.com,
tom@...pey.com, paul@...l-moore.com, jmorris@...ei.org,
serge@...lyn.com, zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
dhowells@...hat.com, jarkko@...nel.org,
stephen.smalley.work@...il.com, eparis@...isplace.org,
mic@...ikod.net
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-nfs@...r.kernel.org, linux-security-module@...r.kernel.org,
linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
selinux@...r.kernel.org, Roberto Sassu <roberto.sassu@...wei.com>,
Stefan Berger <stefanb@...ux.ibm.com>
Subject: Re: [PATCH v5 11/23] security: Introduce inode_post_removexattr hook
On Tue, 2023-11-07 at 09:33 -0800, Casey Schaufler wrote:
> On 11/7/2023 5:40 AM, Roberto Sassu wrote:
> > From: Roberto Sassu <roberto.sassu@...wei.com>
> >
> > In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> > the inode_post_removexattr hook.
> >
> > At inode_removexattr hook, EVM verifies the file's existing HMAC value. At
> > inode_post_removexattr, EVM re-calculates the file's HMAC with the passed
> > xattr removed and other file metadata.
> >
> > Other LSMs could similarly take some action after successful xattr removal.
> >
> > The new hook cannot return an error and cannot cause the operation to be
> > reverted.
> >
> > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> > Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
> > Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
> > ---
> > fs/xattr.c | 9 +++++----
> > include/linux/lsm_hook_defs.h | 2 ++
> > include/linux/security.h | 5 +++++
> > security/security.c | 14 ++++++++++++++
> > 4 files changed, 26 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/xattr.c b/fs/xattr.c
> > index 09d927603433..84a4aa566c02 100644
> > --- a/fs/xattr.c
> > +++ b/fs/xattr.c
> > @@ -552,11 +552,12 @@ __vfs_removexattr_locked(struct mnt_idmap *idmap,
> > goto out;
> >
> > error = __vfs_removexattr(idmap, dentry, name);
> > + if (error)
> > + goto out;
>
> Shouldn't this be simply "return error" rather than a goto to nothing
> but "return error"?
Ok, no problem. I can change that.
Thanks
Roberto
> >
> > - if (!error) {
> > - fsnotify_xattr(dentry);
> > - evm_inode_post_removexattr(dentry, name);
> > - }
> > + fsnotify_xattr(dentry);
> > + security_inode_post_removexattr(dentry, name);
> > + evm_inode_post_removexattr(dentry, name);
> >
> > out:
> > return error;
> > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> > index 67410e085205..88452e45025c 100644
> > --- a/include/linux/lsm_hook_defs.h
> > +++ b/include/linux/lsm_hook_defs.h
> > @@ -149,6 +149,8 @@ LSM_HOOK(int, 0, inode_getxattr, struct dentry *dentry, const char *name)
> > LSM_HOOK(int, 0, inode_listxattr, struct dentry *dentry)
> > 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_set_acl, struct mnt_idmap *idmap,
> > struct dentry *dentry, const char *acl_name, struct posix_acl *kacl)
> > LSM_HOOK(int, 0, inode_get_acl, struct mnt_idmap *idmap,
> > diff --git a/include/linux/security.h b/include/linux/security.h
> > index 664df46b22a9..922ea7709bae 100644
> > --- a/include/linux/security.h
> > +++ b/include/linux/security.h
> > @@ -380,6 +380,7 @@ int security_inode_getxattr(struct dentry *dentry, const char *name);
> > 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_need_killpriv(struct dentry *dentry);
> > int security_inode_killpriv(struct mnt_idmap *idmap, struct dentry *dentry);
> > int security_inode_getsecurity(struct mnt_idmap *idmap,
> > @@ -940,6 +941,10 @@ static inline int security_inode_removexattr(struct mnt_idmap *idmap,
> > return cap_inode_removexattr(idmap, dentry, name);
> > }
> >
> > +static inline void security_inode_post_removexattr(struct dentry *dentry,
> > + const char *name)
> > +{ }
> > +
> > 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 ce3bc7642e18..8aa6e9f316dd 100644
> > --- a/security/security.c
> > +++ b/security/security.c
> > @@ -2452,6 +2452,20 @@ int security_inode_removexattr(struct mnt_idmap *idmap,
> > return evm_inode_removexattr(idmap, dentry, name);
> > }
> >
> > +/**
> > + * security_inode_post_removexattr() - Update the inode after a removexattr op
> > + * @dentry: file
> > + * @name: xattr name
> > + *
> > + * Update the inode after a successful removexattr operation.
> > + */
> > +void security_inode_post_removexattr(struct dentry *dentry, const char *name)
> > +{
> > + if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
> > + return;
> > + call_void_hook(inode_post_removexattr, dentry, name);
> > +}
> > +
> > /**
> > * security_inode_need_killpriv() - Check if security_inode_killpriv() required
> > * @dentry: associated dentry
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