Commit c70d9d80 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

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: default avatarTakashi Iwai <tiwai@suse.de>
Fixes: 64b875f7 ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP")
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 3fd37226

include/linux/ptrace.h

+5 −2
Original line number Diff line number Diff line
@@ -54,7 +54,8 @@ extern int ptrace_request(struct task_struct *child, long request, 
			  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 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace) 


	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 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace) 


		set_tsk_thread_flag(child, TIF_SIGPENDING);

	}

	else

		child->ptracer_cred = NULL;

}



/**

kernel/ptrace.c

+13 −7
Original line number Diff line number Diff line
@@ -60,19 +60,25 @@ int ptrace_access_vm(struct task_struct *tsk, unsigned long addr, 
}





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 @@ static int ptrace_attach(struct task_struct *task, long request, 
		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 @@ static int ptrace_traceme(void) 
		 */

		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);

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