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Message-ID: <8e7705972a0f306922d8bc4893cf940e319abb19.camel@huaweicloud.com>
Date: Wed, 12 Apr 2023 09:22:38 +0200
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: Casey Schaufler <casey@...aufler-ca.com>, zohar@...ux.ibm.com,
dmitry.kasatkin@...il.com, paul@...l-moore.com, jmorris@...ei.org,
serge@...lyn.com, stephen.smalley.work@...il.com,
eparis@...isplace.org
Cc: reiserfs-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
bpf@...r.kernel.org, kpsingh@...nel.org, keescook@...omium.org,
nicolas.bouchinet@...p-os.org,
Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH] Smack modifications for: security: Allow all LSMs to
provide xattrs for inode_init_security hook
On Tue, 2023-04-11 at 10:54 -0700, Casey Schaufler wrote:
> On 4/11/2023 10:23 AM, Roberto Sassu wrote:
> > From: Roberto Sassu <roberto.sassu@...wei.com>
> >
> > Very very quick modification. Not tested.
> >
> > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> > ---
> > security/smack/smack.h | 2 +-
> > security/smack/smack_lsm.c | 42 ++++++++++++++++++++------------------
> > 2 files changed, 23 insertions(+), 21 deletions(-)
> >
> > diff --git a/security/smack/smack.h b/security/smack/smack.h
> > index e2239be7bd6..f00c8498c60 100644
> > --- a/security/smack/smack.h
> > +++ b/security/smack/smack.h
> > @@ -127,7 +127,7 @@ struct task_smack {
> >
> > #define SMK_INODE_INSTANT 0x01 /* inode is instantiated */
> > #define SMK_INODE_TRANSMUTE 0x02 /* directory is transmuting */
> > -#define SMK_INODE_CHANGED 0x04 /* smack was transmuted */
> > +#define SMK_INODE_CHANGED 0x04 /* smack was transmuted (unused) */
>
> See below ...
>
> > #define SMK_INODE_IMPURE 0x08 /* involved in an impure transaction */
> >
> > /*
> > diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> > index 8392983334b..b43820bdbd0 100644
> > --- a/security/smack/smack_lsm.c
> > +++ b/security/smack/smack_lsm.c
> > @@ -54,12 +54,12 @@
> >
> > /*
> > * Smack uses multiple xattrs.
> > - * SMACK64 - for access control, SMACK64EXEC - label for the program,
> > - * SMACK64MMAP - controls library loading,
> > + * SMACK64 - for access control,
> > * SMACK64TRANSMUTE - label initialization,
> > - * Not saved on files - SMACK64IPIN and SMACK64IPOUT
> > + * Not saved on files - SMACK64IPIN and SMACK64IPOUT,
> > + * Must be set explicitly - SMACK64EXEC and SMACK64MMAP
> > */
> > -#define SMACK_INODE_INIT_XATTRS 4
> > +#define SMACK_INODE_INIT_XATTRS 2
> >
> > #ifdef SMACK_IPV6_PORT_LABELING
> > static DEFINE_MUTEX(smack_ipv6_lock);
> > @@ -957,11 +957,11 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
> > const struct qstr *qstr,
> > struct xattr *xattrs, int *xattr_count)
> > {
> > - struct inode_smack *issp = smack_inode(inode);
> > struct smack_known *skp = smk_of_current();
> > struct smack_known *isp = smk_of_inode(inode);
> > struct smack_known *dsp = smk_of_inode(dir);
> > struct xattr *xattr = lsm_get_xattr_slot(xattrs, xattr_count);
> > + struct xattr *xattr2;
>
> I'm going to channel Paul and suggest this be xattr_transmute instead of xattr2.
> It also looks like it could move to be declared in the if clause.
>
> > int may;
> >
> > if (xattr) {
> > @@ -979,7 +979,17 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
> > if (may > 0 && ((may & MAY_TRANSMUTE) != 0) &&
> > smk_inode_transmutable(dir)) {
> > isp = dsp;
> > - issp->smk_flags |= SMK_INODE_CHANGED;
>
> I think you need to keep this. More below.
>
> > + xattr2 = lsm_get_xattr_slot(xattrs, xattr_count);
> > + if (xattr2) {
> > + xattr2->value = kmemdup(TRANS_TRUE,
> > + TRANS_TRUE_SIZE,
> > + GFP_NOFS);
> > + if (xattr2->value == NULL)
> > + return -ENOMEM;
> > +
> > + xattr2->value_len = TRANS_TRUE_SIZE;
> > + xattr2->name = XATTR_NAME_SMACKTRANSMUTE;
> > + }
> > }
> >
> > xattr->value = kstrdup(isp->smk_known, GFP_NOFS);
> > @@ -3512,20 +3522,12 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
> > * If there is a transmute attribute on the
> > * directory mark the inode.
> > */
> > - if (isp->smk_flags & SMK_INODE_CHANGED) {
> > - isp->smk_flags &= ~SMK_INODE_CHANGED;
> > - rc = __vfs_setxattr(&nop_mnt_idmap, dp, inode,
> > - XATTR_NAME_SMACKTRANSMUTE,
> > - TRANS_TRUE, TRANS_TRUE_SIZE,
> > - 0);
> > - } else {
> > - rc = __vfs_getxattr(dp, inode,
> > - XATTR_NAME_SMACKTRANSMUTE, trattr,
> > - TRANS_TRUE_SIZE);
> > - if (rc >= 0 && strncmp(trattr, TRANS_TRUE,
> > - TRANS_TRUE_SIZE) != 0)
> > - rc = -EINVAL;
> > - }
> > + rc = __vfs_getxattr(dp, inode,
> > + XATTR_NAME_SMACKTRANSMUTE, trattr,
> > + TRANS_TRUE_SIZE);
> > + if (rc >= 0 && strncmp(trattr, TRANS_TRUE,
> > + TRANS_TRUE_SIZE) != 0)
> > + rc = -EINVAL;
>
> Where is the SMACK64_TRANSMUTE attribute going to get set on the file?
> It's not going to get set in smack_init_inode_security(). The inode will
Isn't that the purpose of the inode_init_security hook?
After all LSMs provide one or multiple xattrs, xattrs are going to be
written to the disk with the initxattr() callback of filesystems.
There is a small mistake above (XATTR_SMACK_TRANSMUTE instead
of XATTR_NAME_SMACKTRANSMUTE, as we are providing just the suffix).
After fixing that, Smack tests succeed:
95 Passed, 0 Failed, 100% Success rate
There was a test failing in dir-transmute.sh, before I fixed the xattr
name.
Thanks
Roberto
> know it's transmuting, but it won't get to disk without the __vfs_setxattr()
> here in smack_d_instantiate(). Now, it's been a long time since that code
> was written, so I could be wrong, but I'm pretty sure about that.
>
> I think that you should be fine with the changes in smack_init_inode_security(),
> and leaving smack_d_instantiate() untouched.
>
> > if (rc >= 0)
> > transflag = SMK_INODE_TRANSMUTE;
> > }
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