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Message-ID: <5583007A.8040704@tycho.nsa.gov>
Date: Thu, 18 Jun 2015 13:31:38 -0400
From: Stephen Smalley <sds@...ho.nsa.gov>
To: David Howells <dhowells@...hat.com>
CC: linux-fsdevel@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org,
SELinux <selinux@...ho.nsa.gov>, Paul Moore <paul@...l-moore.com>
Subject: Re: [PATCH] SELinux: Create a common helper to determine an inode
label [ver #2]
On 06/18/2015 01:08 PM, Stephen Smalley wrote:
> On 06/18/2015 12:41 PM, David Howells wrote:
>> SELinux: Create a common helper to determine an inode label
>>
>> Create a common helper function to determine the label for a new inode.
>> This is then used by:
>>
>> - may_create()
>> - selinux_dentry_init_security()
>> - selinux_inode_init_security()
>>
>> This will change the behaviour of the functions slightly, bringing them all
>> into line.
>>
>> Suggested-by: Stephen Smalley <sds@...ho.nsa.gov>
>> Signed-off-by: David Howells <dhowells@...hat.com>
>> ---
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index ffa5a642629a..902113d71acd 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -1684,6 +1684,32 @@ out:
>> return rc;
>> }
>>
>> +/*
>> + * Determine the label for an inode that might be unioned.
>> + */
>> +static int selinux_determine_inode_label(const struct inode *dir,
>> + const struct qstr *name,
>> + u16 tclass,
>> + u32 *_new_isid)
>> +{
>> + const struct superblock_security_struct *sbsec = dir->i_sb->s_security;
>> + const struct inode_security_struct *dsec = dir->i_security;
>> + const struct task_security_struct *tsec = current_security();
>> +
>> + if ((sbsec->flags & SE_SBINITIALIZED) &&
>> + (sbsec->behavior == SECURITY_FS_USE_MNTPOINT)) {
>> + *_new_isid = sbsec->mntpoint_sid;
>> + } else if ((sbsec->flags & SBLABEL_MNT) &&
>> + tsec->create_sid) {
>> + *_new_isid = tsec->create_sid;
>> + } else {
>> + return security_transition_sid(tsec->sid, dsec->sid, tclass,
>> + name, _new_isid);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> /* Check whether a task can create a file. */
>> static int may_create(struct inode *dir,
>> struct dentry *dentry,
>> @@ -1700,7 +1726,6 @@ static int may_create(struct inode *dir,
>> sbsec = dir->i_sb->s_security;
>>
>> sid = tsec->sid;
>> - newsid = tsec->create_sid;
>>
>> ad.type = LSM_AUDIT_DATA_DENTRY;
>> ad.u.dentry = dentry;
>> @@ -1711,12 +1736,10 @@ static int may_create(struct inode *dir,
>> if (rc)
>> return rc;
>>
>> - if (!newsid || !(sbsec->flags & SBLABEL_MNT)) {
>> - rc = security_transition_sid(sid, dsec->sid, tclass,
>> - &dentry->d_name, &newsid);
>> - if (rc)
>> - return rc;
>> - }
>> + rc = selinux_determine_inode_label(dir, &dentry->d_name, tclass,
>> + &newsid);
>> + if (rc)
>> + return rc;
>>
>> rc = avc_has_perm(sid, newsid, tclass, FILE__CREATE, &ad);
>> if (rc)
>> @@ -2723,32 +2746,14 @@ static int selinux_dentry_init_security(struct dentry *dentry, int mode,
>> struct qstr *name, void **ctx,
>> u32 *ctxlen)
>> {
>> - const struct cred *cred = current_cred();
>> - struct task_security_struct *tsec;
>> - struct inode_security_struct *dsec;
>> - struct superblock_security_struct *sbsec;
>> - struct inode *dir = d_backing_inode(dentry->d_parent);
>> u32 newsid;
>> int rc;
>>
>> - tsec = cred->security;
>> - dsec = dir->i_security;
>> - sbsec = dir->i_sb->s_security;
>> -
>> - if (tsec->create_sid && sbsec->behavior != SECURITY_FS_USE_MNTPOINT) {
>> - newsid = tsec->create_sid;
>> - } else {
>> - rc = security_transition_sid(tsec->sid, dsec->sid,
>> - inode_mode_to_security_class(mode),
>> - name,
>> - &newsid);
>> - if (rc) {
>> - printk(KERN_WARNING
>> - "%s: security_transition_sid failed, rc=%d\n",
>> - __func__, -rc);
>> - return rc;
>> - }
>> - }
>> + rc = selinux_determine_inode_label(d_inode(dentry), name,
>
> We want d_inode(dentry->d_parent) here.
Not sure why the caller didn't just pass in the dir inode in the first
place.
>
>> + inode_mode_to_security_class(mode),
>> + &newsid);
>> + if (rc)
>> + return rc;
>>
>> return security_sid_to_context(newsid, (char **)ctx, ctxlen);
>> }
>> @@ -2771,22 +2776,12 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
>> sid = tsec->sid;
>> newsid = tsec->create_sid;
>>
>> - if ((sbsec->flags & SE_SBINITIALIZED) &&
>> - (sbsec->behavior == SECURITY_FS_USE_MNTPOINT))
>> - newsid = sbsec->mntpoint_sid;
>> - else if (!newsid || !(sbsec->flags & SBLABEL_MNT)) {
>> - rc = security_transition_sid(sid, dsec->sid,
>> - inode_mode_to_security_class(inode->i_mode),
>> - qstr, &newsid);
>> - if (rc) {
>> - printk(KERN_WARNING "%s: "
>> - "security_transition_sid failed, rc=%d (dev=%s "
>> - "ino=%ld)\n",
>> - __func__,
>> - -rc, inode->i_sb->s_id, inode->i_ino);
>> - return rc;
>> - }
>> - }
>> + rc = selinux_determine_inode_label(
>> + dir, qstr,
>> + inode_mode_to_security_class(inode->i_mode),
>> + &newsid);
>> + if (rc)
>> + return rc;
>>
>> /* Possibly defer initialization to selinux_complete_init. */
>> if (sbsec->flags & SE_SBINITIALIZED) {
>>
>>
>
--
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