ptrace: Properly initialize ptracer_cred on fork
When I introduced ptracer_cred I failed to consider the weirdness of
fork where the task_struct copies the old value by default. This
winds up leaving ptracer_cred set even when a process forks and
the child process does not wind up being ptraced.
Because ptracer_cred is not set on non-ptraced processes whose
parents were ptraced this has broken the ability of the enlightenment
window manager to start setuid children.
Fix this by properly initializing ptracer_cred in ptrace_init_task
This must be done with a little bit of care to preserve the current value
of ptracer_cred when ptrace carries through fork. Re-reading the
ptracer_cred from the ptracing process at this point is inconsistent
with how PT_PTRACE_CAP has been maintained all of these years.
Tested-by: Takashi Iwai <tiwai@suse.de>
Fixes: 64b875f7ac8a ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 422bc2e..ef3eb8b 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -54,7 +54,8 @@
unsigned long addr, unsigned long data);
extern void ptrace_notify(int exit_code);
extern void __ptrace_link(struct task_struct *child,
- struct task_struct *new_parent);
+ struct task_struct *new_parent,
+ const struct cred *ptracer_cred);
extern void __ptrace_unlink(struct task_struct *child);
extern void exit_ptrace(struct task_struct *tracer, struct list_head *dead);
#define PTRACE_MODE_READ 0x01
@@ -206,7 +207,7 @@
if (unlikely(ptrace) && current->ptrace) {
child->ptrace = current->ptrace;
- __ptrace_link(child, current->parent);
+ __ptrace_link(child, current->parent, current->ptracer_cred);
if (child->ptrace & PT_SEIZED)
task_set_jobctl_pending(child, JOBCTL_TRAP_STOP);
@@ -215,6 +216,8 @@
set_tsk_thread_flag(child, TIF_SIGPENDING);
}
+ else
+ child->ptracer_cred = NULL;
}
/**
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 266ddcc..60f356d 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -60,19 +60,25 @@
}
+void __ptrace_link(struct task_struct *child, struct task_struct *new_parent,
+ const struct cred *ptracer_cred)
+{
+ BUG_ON(!list_empty(&child->ptrace_entry));
+ list_add(&child->ptrace_entry, &new_parent->ptraced);
+ child->parent = new_parent;
+ child->ptracer_cred = get_cred(ptracer_cred);
+}
+
/*
* ptrace a task: make the debugger its new parent and
* move it to the ptrace list.
*
* Must be called with the tasklist lock write-held.
*/
-void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
+static void ptrace_link(struct task_struct *child, struct task_struct *new_parent)
{
- BUG_ON(!list_empty(&child->ptrace_entry));
- list_add(&child->ptrace_entry, &new_parent->ptraced);
- child->parent = new_parent;
rcu_read_lock();
- child->ptracer_cred = get_cred(__task_cred(new_parent));
+ __ptrace_link(child, new_parent, __task_cred(new_parent));
rcu_read_unlock();
}
@@ -386,7 +392,7 @@
flags |= PT_SEIZED;
task->ptrace = flags;
- __ptrace_link(task, current);
+ ptrace_link(task, current);
/* SEIZE doesn't trap tracee on attach */
if (!seize)
@@ -459,7 +465,7 @@
*/
if (!ret && !(current->real_parent->flags & PF_EXITING)) {
current->ptrace = PT_PTRACED;
- __ptrace_link(current, current->real_parent);
+ ptrace_link(current, current->real_parent);
}
}
write_unlock_irq(&tasklist_lock);
