[PATCH v3 1/3] ptrace: Provide ___ptrace_may_access() that can be applied on arbitrary tasks

Jiri Kosina
2018-09-04T14:41:38Z

From: Jiri Kosina <jkosina@suse.cz>

Current ptrace_may_access() implementation assumes that the 'source' task is
always the caller (current).

Expose ___ptrace_may_access() that can be used to apply the check on arbitrary
tasks.

Originally-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
---

Sorry for the resend, my pine is buggered and broke threading.

include/linux/ptrace.h | 12 ++++++++++++
kernel/ptrace.c | 13 ++++++++++---
2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 4f36431c380b..09744d4113fb 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -87,6 +87,18 @@ extern void exit_ptrace(struct task_struct *tracer, struct list_head *dead);
*/
extern bool ptrace_may_access(struct task_struct *task, unsigned int mode);

+/**
+ * ___ptrace_may_access - variant of ptrace_may_access that can be used
+ * between two arbitrary tasks
+ * @curr: source task
+ * @task: target task
+ * @mode: selects type of access and caller credentials
+ *
+ * Returns true on success, false on denial.
+ */
+extern int ___ptrace_may_access(struct task_struct *curr, struct task_struct *task,
+ unsigned int mode);
+
static inline int ptrace_reparented(struct task_struct *child)
{
return !same_thread_group(child->real_parent, child->parent);
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 21fec73d45d4..07ff6685ebed 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -268,9 +268,10 @@ static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode)
}

/* Returns 0 on success, -errno on denial. */
-static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
+int ___ptrace_may_access(struct task_struct *curr, struct task_struct *task,
+ unsigned int mode)
{
- const struct cred *cred = current_cred(), *tcred;
+ const struct cred *cred, *tcred;
struct mm_struct *mm;
kuid_t caller_uid;
kgid_t caller_gid;
@@ -290,9 +291,10 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
*/

/* Don't let security modules deny introspection */
- if (same_thread_group(task, current))
+ if (same_thread_group(task, curr))
return 0;
rcu_read_lock();
+ cred = __task_cred(curr);
if (mode & PTRACE_MODE_FSCREDS) {
caller_uid = cred->fsuid;
caller_gid = cred->fsgid;
@@ -331,6 +333,11 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
return security_ptrace_access_check(task, mode);
}

+static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
+{
+ return ___ptrace_may_access(current, task, mode);
+}
+
bool ptrace_may_access(struct task_struct *task, unsigned int mode)
{
int err;

--
Jiri Kosina
SUSE Labs