[RFC PATCH 3/4] smack: differentiate between subjective and objective task credentials

[John Johansen]

On 2/19/21 3:29 PM, Paul Moore wrote:
> With the split of the security_task_getsecid() into subjective and
> objective variants it's time to update Smack to ensure it is using
> the correct task creds.
> 
> Signed-off-by: Paul Moore <paul at paul-moore.com>

first pass looks good to me

> ---
>  security/smack/smack.h     |   18 +++++++++++++++++-
>  security/smack/smack_lsm.c |   40 +++++++++++++++++++++++++++-------------
>  2 files changed, 44 insertions(+), 14 deletions(-)
> 
> diff --git a/security/smack/smack.h b/security/smack/smack.h
> index a9768b12716bf..08f9cb80655ce 100644
> --- a/security/smack/smack.h
> +++ b/security/smack/smack.h
> @@ -383,7 +383,23 @@ static inline struct smack_known *smk_of_task(const struct task_smack *tsp)
>  	return tsp->smk_task;
>  }
>  
> -static inline struct smack_known *smk_of_task_struct(
> +static inline struct smack_known *smk_of_task_struct_subj(
> +						const struct task_struct *t)
> +{
> +	struct smack_known *skp;
> +	const struct cred *cred;
> +
> +	rcu_read_lock();
> +
> +	cred = rcu_dereference(t->cred);
> +	skp = smk_of_task(smack_cred(cred));
> +
> +	rcu_read_unlock();
> +
> +	return skp;
> +}
> +
> +static inline struct smack_known *smk_of_task_struct_obj(
>  						const struct task_struct *t)
>  {
>  	struct smack_known *skp;
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 2bb354ef2c4a9..ea1a82742e8ba 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -159,7 +159,7 @@ static int smk_bu_current(char *note, struct smack_known *oskp,
>  static int smk_bu_task(struct task_struct *otp, int mode, int rc)
>  {
>  	struct task_smack *tsp = smack_cred(current_cred());
> -	struct smack_known *smk_task = smk_of_task_struct(otp);
> +	struct smack_known *smk_task = smk_of_task_struct_obj(otp);
>  	char acc[SMK_NUM_ACCESS_TYPE + 1];
>  
>  	if (rc <= 0)
> @@ -479,7 +479,7 @@ static int smack_ptrace_access_check(struct task_struct *ctp, unsigned int mode)
>  {
>  	struct smack_known *skp;
>  
> -	skp = smk_of_task_struct(ctp);
> +	skp = smk_of_task_struct_obj(ctp);
>  
>  	return smk_ptrace_rule_check(current, skp, mode, __func__);
>  }
> @@ -2031,7 +2031,7 @@ static int smk_curacc_on_task(struct task_struct *p, int access,
>  				const char *caller)
>  {
>  	struct smk_audit_info ad;
> -	struct smack_known *skp = smk_of_task_struct(p);
> +	struct smack_known *skp = smk_of_task_struct_subj(p);
>  	int rc;
>  
>  	smk_ad_init(&ad, caller, LSM_AUDIT_DATA_TASK);
> @@ -2076,15 +2076,29 @@ static int smack_task_getsid(struct task_struct *p)
>  }
>  
>  /**
> - * smack_task_getsecid - get the secid of the task
> - * @p: the object task
> + * smack_task_getsecid_subj - get the subjective secid of the task
> + * @p: the task
>   * @secid: where to put the result
>   *
> - * Sets the secid to contain a u32 version of the smack label.
> + * Sets the secid to contain a u32 version of the task's subjective smack label.
> + */
> +static void smack_task_getsecid_subj(struct task_struct *p, u32 *secid)
> +{
> +	struct smack_known *skp = smk_of_task_struct_subj(p);
> +
> +	*secid = skp->smk_secid;
> +}
> +
> +/**
> + * smack_task_getsecid_obj - get the objective secid of the task
> + * @p: the task
> + * @secid: where to put the result
> + *
> + * Sets the secid to contain a u32 version of the task's objective smack label.
>   */
> -static void smack_task_getsecid(struct task_struct *p, u32 *secid)
> +static void smack_task_getsecid_obj(struct task_struct *p, u32 *secid)
>  {
> -	struct smack_known *skp = smk_of_task_struct(p);
> +	struct smack_known *skp = smk_of_task_struct_obj(p);
>  
>  	*secid = skp->smk_secid;
>  }
> @@ -2172,7 +2186,7 @@ static int smack_task_kill(struct task_struct *p, struct kernel_siginfo *info,
>  {
>  	struct smk_audit_info ad;
>  	struct smack_known *skp;
> -	struct smack_known *tkp = smk_of_task_struct(p);
> +	struct smack_known *tkp = smk_of_task_struct_obj(p);
>  	int rc;
>  
>  	if (!sig)
> @@ -2210,7 +2224,7 @@ static int smack_task_kill(struct task_struct *p, struct kernel_siginfo *info,
>  static void smack_task_to_inode(struct task_struct *p, struct inode *inode)
>  {
>  	struct inode_smack *isp = smack_inode(inode);
> -	struct smack_known *skp = smk_of_task_struct(p);
> +	struct smack_known *skp = smk_of_task_struct_obj(p);
>  
>  	isp->smk_inode = skp;
>  	isp->smk_flags |= SMK_INODE_INSTANT;
> @@ -3481,7 +3495,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
>   */
>  static int smack_getprocattr(struct task_struct *p, char *name, char **value)
>  {
> -	struct smack_known *skp = smk_of_task_struct(p);
> +	struct smack_known *skp = smk_of_task_struct_subj(p);
>  	char *cp;
>  	int slen;
>  
> @@ -4755,8 +4769,8 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
>  	LSM_HOOK_INIT(task_setpgid, smack_task_setpgid),
>  	LSM_HOOK_INIT(task_getpgid, smack_task_getpgid),
>  	LSM_HOOK_INIT(task_getsid, smack_task_getsid),
> -	LSM_HOOK_INIT(task_getsecid_subj, smack_task_getsecid),
> -	LSM_HOOK_INIT(task_getsecid_obj, smack_task_getsecid),
> +	LSM_HOOK_INIT(task_getsecid_subj, smack_task_getsecid_subj),
> +	LSM_HOOK_INIT(task_getsecid_obj, smack_task_getsecid_obj),
>  	LSM_HOOK_INIT(task_setnice, smack_task_setnice),
>  	LSM_HOOK_INIT(task_setioprio, smack_task_setioprio),
>  	LSM_HOOK_INIT(task_getioprio, smack_task_getioprio),
>