Commit 3ab67966 authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

uprobes: Teach uprobe_copy_process() to handle CLONE_VFORK 



uprobe_copy_process() does nothing if the child shares ->mm with
the forking process, but there is a special case: CLONE_VFORK.
In this case it would be more correct to do dup_utask() but avoid
dup_xol(). This is not that important, the child should not unwind
its stack too much, this can corrupt the parent's stack, but at
least we need this to allow to ret-probe __vfork() itself.

Note: in theory, it would be better to check task_pt_regs(p)->sp
instead of CLONE_VFORK, we need to dup_utask() if and only if the
child can return from the function called by the parent. But this
needs the arch-dependant helper, and I think that nobody actually
does clone(same_stack, CLONE_VM).

Reported-by: default avatarMartin Cermak <mcermak@redhat.com>
Reported-by: default avatarDavid Smith <dsmith@redhat.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
parent aa59c53f

include/linux/uprobes.h

+2 −2
Original line number Diff line number Diff line
@@ -117,7 +117,7 @@ extern void uprobe_start_dup_mmap(void); 
extern void uprobe_end_dup_mmap(void);

extern void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm);

extern void uprobe_free_utask(struct task_struct *t);

extern void uprobe_copy_process(struct task_struct *t);

extern void uprobe_copy_process(struct task_struct *t, unsigned long flags);

extern unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs);

extern int uprobe_post_sstep_notifier(struct pt_regs *regs);

extern int uprobe_pre_sstep_notifier(struct pt_regs *regs);
@@ -174,7 +174,7 @@ static inline unsigned long uprobe_get_swbp_addr(struct pt_regs *regs) 
static inline void uprobe_free_utask(struct task_struct *t)

{

}

static inline void uprobe_copy_process(struct task_struct *t)

static inline void uprobe_copy_process(struct task_struct *t, unsigned long flags)

{

}

static inline void uprobe_clear_state(struct mm_struct *mm)

kernel/events/uprobes.c

+8 −2
Original line number Diff line number Diff line
@@ -1415,7 +1415,7 @@ static void dup_xol_work(struct callback_head *work) 
/*

 * Called in context of a new clone/fork from copy_process.

 */

void uprobe_copy_process(struct task_struct *t)

void uprobe_copy_process(struct task_struct *t, unsigned long flags)

{

	struct uprobe_task *utask = current->utask;

	struct mm_struct *mm = current->mm;
@@ -1424,7 +1424,10 @@ void uprobe_copy_process(struct task_struct *t) 


	t->utask = NULL;



	if (mm == t->mm || !utask || !utask->return_instances)

	if (!utask || !utask->return_instances)

		return;



	if (mm == t->mm && !(flags & CLONE_VFORK))

		return;



	if (dup_utask(t, utask))
@@ -1435,6 +1438,9 @@ void uprobe_copy_process(struct task_struct *t) 
	if (!area)

		return uprobe_warn(t, "dup xol area");



	if (mm == t->mm)

		return;



	/* TODO: move it into the union in uprobe_task */

	work = kmalloc(sizeof(*work), GFP_KERNEL);

	if (!work)

kernel/fork.c

+1 −1
Original line number Diff line number Diff line
@@ -1489,7 +1489,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
	perf_event_fork(p);



	trace_task_newtask(p, clone_flags);

	uprobe_copy_process(p);

	uprobe_copy_process(p, clone_flags);



	return p;

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