On 2/19/21 3:29 PM, Paul Moore wrote:
> SELinux has a function, task_sid(), which returns the task's
> objective credentials, but unfortunately is used in a few places
> where the subjective task credentials should be used. Most notably
> in the new security_task_getsecid_subj() LSM hook.
>
> This patch fixes this and attempts to make things more obvious by
> introducing a new function, task_sid_subj(), and renaming the
> existing task_sid() function to task_sid_obj().
>
> Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx>
I have a couple of questions below but the rest looks good
> ---
> security/selinux/hooks.c | 85 +++++++++++++++++++++++++++-------------------
> 1 file changed, 49 insertions(+), 36 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index f311541c4972e..1c53000d28e37 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -229,10 +229,23 @@ static inline u32 cred_sid(const struct cred *cred)
> return tsec->sid;
> }
>
> +/*
> + * get the subjective security ID of a task
> + */
> +static inline u32 task_sid_subj(const struct task_struct *task)
> +{
> + u32 sid;
> +
> + rcu_read_lock();
> + sid = cred_sid(rcu_dereference(task->cred));
> + rcu_read_unlock();
> + return sid;
> +}
> +
> /*
> * get the objective security ID of a task
> */
> -static inline u32 task_sid(const struct task_struct *task)
> +static inline u32 task_sid_obj(const struct task_struct *task)
> {
> u32 sid;
>
> @@ -2034,11 +2047,8 @@ static inline u32 open_file_to_av(struct file *file)
>
> static int selinux_binder_set_context_mgr(struct task_struct *mgr)
> {
> - u32 mysid = current_sid();
> - u32 mgrsid = task_sid(mgr);
> -
> return avc_has_perm(&selinux_state,
> - mysid, mgrsid, SECCLASS_BINDER,
> + current_sid(), task_sid_obj(mgr), SECCLASS_BINDER,
> BINDER__SET_CONTEXT_MGR, NULL);
> }
>
> @@ -2046,8 +2056,8 @@ static int selinux_binder_transaction(struct task_struct *from,
> struct task_struct *to)
> {
> u32 mysid = current_sid();
> - u32 fromsid = task_sid(from);
> - u32 tosid = task_sid(to);
> + u32 fromsid = task_sid_subj(from);
fromsid potentially gets used as both the subject and the object the following
permission checks. It makes sense to use the same cred for both checks but
what I am not sure about yet is whether its actually safe to use the subject
sid when the task isn't current.
ie. I am still trying to determine if there is a race here between the transaction
request and the permission check.
> + u32 tosid = task_sid_subj(to);
its not clear to me that using the subj for to is correct
> int rc;
>
> if (mysid != fromsid) {
> @@ -2066,11 +2076,9 @@ static int selinux_binder_transaction(struct task_struct *from,
> static int selinux_binder_transfer_binder(struct task_struct *from,
> struct task_struct *to)
> {
> - u32 fromsid = task_sid(from);
> - u32 tosid = task_sid(to);
> -
> return avc_has_perm(&selinux_state,
> - fromsid, tosid, SECCLASS_BINDER, BINDER__TRANSFER,
> + task_sid_subj(from), task_sid_obj(to),
> + SECCLASS_BINDER, BINDER__TRANSFER,
> NULL);
> }
>
> @@ -2078,7 +2086,7 @@ static int selinux_binder_transfer_file(struct task_struct *from,
> struct task_struct *to,
> struct file *file)
> {
> - u32 sid = task_sid(to);
> + u32 sid = task_sid_subj(to);
same question about safety here
> struct file_security_struct *fsec = selinux_file(file);
> struct dentry *dentry = file->f_path.dentry;
> struct inode_security_struct *isec;
> @@ -2114,10 +2122,10 @@ static int selinux_binder_transfer_file(struct task_struct *from,
> }
>
> static int selinux_ptrace_access_check(struct task_struct *child,
> - unsigned int mode)
> + unsigned int mode)
> {
> u32 sid = current_sid();
> - u32 csid = task_sid(child);
> + u32 csid = task_sid_obj(child);
>
> if (mode & PTRACE_MODE_READ)
> return avc_has_perm(&selinux_state,
> @@ -2130,15 +2138,15 @@ static int selinux_ptrace_access_check(struct task_struct *child,
> static int selinux_ptrace_traceme(struct task_struct *parent)
> {
> return avc_has_perm(&selinux_state,
> - task_sid(parent), current_sid(), SECCLASS_PROCESS,
> - PROCESS__PTRACE, NULL);
> + task_sid_subj(parent), task_sid_obj(current),
> + SECCLASS_PROCESS, PROCESS__PTRACE, NULL);
> }
>
> static int selinux_capget(struct task_struct *target, kernel_cap_t *effective,
> kernel_cap_t *inheritable, kernel_cap_t *permitted)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(target), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(target), SECCLASS_PROCESS,
> PROCESS__GETCAP, NULL);
> }
>
> @@ -2263,7 +2271,7 @@ static u32 ptrace_parent_sid(void)
> rcu_read_lock();
> tracer = ptrace_parent(current);
> if (tracer)
> - sid = task_sid(tracer);
> + sid = task_sid_obj(tracer);
> rcu_read_unlock();
>
> return sid;
> @@ -3916,7 +3924,7 @@ static int selinux_file_send_sigiotask(struct task_struct *tsk,
> struct fown_struct *fown, int signum)
> {
> struct file *file;
> - u32 sid = task_sid(tsk);
> + u32 sid = task_sid_obj(tsk);
> u32 perm;
> struct file_security_struct *fsec;
>
> @@ -4135,47 +4143,52 @@ static int selinux_kernel_load_data(enum kernel_load_data_id id, bool contents)
> static int selinux_task_setpgid(struct task_struct *p, pid_t pgid)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(p), SECCLASS_PROCESS,
> PROCESS__SETPGID, NULL);
> }
>
> static int selinux_task_getpgid(struct task_struct *p)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(p), SECCLASS_PROCESS,
> PROCESS__GETPGID, NULL);
> }
>
> static int selinux_task_getsid(struct task_struct *p)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(p), SECCLASS_PROCESS,
> PROCESS__GETSESSION, NULL);
> }
>
> -static void selinux_task_getsecid(struct task_struct *p, u32 *secid)
> +static void selinux_task_getsecid_subj(struct task_struct *p, u32 *secid)
> +{
> + *secid = task_sid_subj(p);
> +}
> +
> +static void selinux_task_getsecid_obj(struct task_struct *p, u32 *secid)
> {
> - *secid = task_sid(p);
> + *secid = task_sid_obj(p);
> }
>
> static int selinux_task_setnice(struct task_struct *p, int nice)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(p), SECCLASS_PROCESS,
> PROCESS__SETSCHED, NULL);
> }
>
> static int selinux_task_setioprio(struct task_struct *p, int ioprio)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(p), SECCLASS_PROCESS,
> PROCESS__SETSCHED, NULL);
> }
>
> static int selinux_task_getioprio(struct task_struct *p)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(p), SECCLASS_PROCESS,
> PROCESS__GETSCHED, NULL);
> }
>
> @@ -4206,7 +4219,7 @@ static int selinux_task_setrlimit(struct task_struct *p, unsigned int resource,
> upon context transitions. See selinux_bprm_committing_creds. */
> if (old_rlim->rlim_max != new_rlim->rlim_max)
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p),
> + current_sid(), task_sid_obj(p),
> SECCLASS_PROCESS, PROCESS__SETRLIMIT, NULL);
>
> return 0;
> @@ -4215,21 +4228,21 @@ static int selinux_task_setrlimit(struct task_struct *p, unsigned int resource,
> static int selinux_task_setscheduler(struct task_struct *p)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(p), SECCLASS_PROCESS,
> PROCESS__SETSCHED, NULL);
> }
>
> static int selinux_task_getscheduler(struct task_struct *p)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(p), SECCLASS_PROCESS,
> PROCESS__GETSCHED, NULL);
> }
>
> static int selinux_task_movememory(struct task_struct *p)
> {
> return avc_has_perm(&selinux_state,
> - current_sid(), task_sid(p), SECCLASS_PROCESS,
> + current_sid(), task_sid_obj(p), SECCLASS_PROCESS,
> PROCESS__SETSCHED, NULL);
> }
>
> @@ -4248,14 +4261,14 @@ static int selinux_task_kill(struct task_struct *p, struct kernel_siginfo *info,
> else
> secid = cred_sid(cred);
> return avc_has_perm(&selinux_state,
> - secid, task_sid(p), SECCLASS_PROCESS, perm, NULL);
> + secid, task_sid_obj(p), SECCLASS_PROCESS, perm, NULL);
> }
>
> static void selinux_task_to_inode(struct task_struct *p,
> struct inode *inode)
> {
> struct inode_security_struct *isec = selinux_inode(inode);
> - u32 sid = task_sid(p);
> + u32 sid = task_sid_obj(p);
>
> spin_lock(&isec->lock);
> isec->sclass = inode_mode_to_security_class(inode->i_mode);
> @@ -6148,7 +6161,7 @@ static int selinux_msg_queue_msgrcv(struct kern_ipc_perm *msq, struct msg_msg *m
> struct ipc_security_struct *isec;
> struct msg_security_struct *msec;
> struct common_audit_data ad;
> - u32 sid = task_sid(target);
> + u32 sid = task_sid_subj(target);
> int rc;
>
> isec = selinux_ipc(msq);
> @@ -7143,8 +7156,8 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
> LSM_HOOK_INIT(task_setpgid, selinux_task_setpgid),
> LSM_HOOK_INIT(task_getpgid, selinux_task_getpgid),
> LSM_HOOK_INIT(task_getsid, selinux_task_getsid),
> - LSM_HOOK_INIT(task_getsecid_subj, selinux_task_getsecid),
> - LSM_HOOK_INIT(task_getsecid_obj, selinux_task_getsecid),
> + LSM_HOOK_INIT(task_getsecid_subj, selinux_task_getsecid_subj),
> + LSM_HOOK_INIT(task_getsecid_obj, selinux_task_getsecid_obj),
> LSM_HOOK_INIT(task_setnice, selinux_task_setnice),
> LSM_HOOK_INIT(task_setioprio, selinux_task_setioprio),
> LSM_HOOK_INIT(task_getioprio, selinux_task_getioprio),
>
