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

[Jiri Kosina]

From: Jiri Kosina <jkos...@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.c...@linux.intel.com>
Signed-off-by: Jiri Kosina <jkos...@suse.cz>
---
 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