x86, ptrace, mm: fix double-free on race

Ptrace_detach() races with __ptrace_unlink() if the traced task is
reaped while detaching. This might cause a double-free of the BTS
buffer.

Change the ptrace_detach() path to only do the memory accounting in
ptrace_bts_detach() and leave the buffer free to ptrace_bts_untrace()
which will be called from __ptrace_unlink().

The fix follows a proposal from Oleg Nesterov.

Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Markus Metzger 2009-02-11 15:10:27 +01:00 committed by Ingo Molnar
parent 06eb23b1ba
commit 9f339e7028
3 changed files with 17 additions and 7 deletions

View file

@ -810,12 +810,16 @@ static void ptrace_bts_untrace(struct task_struct *child)
static void ptrace_bts_detach(struct task_struct *child)
{
if (unlikely(child->bts)) {
ds_release_bts(child->bts);
child->bts = NULL;
ptrace_bts_free_buffer(child);
}
/*
* Ptrace_detach() races with ptrace_untrace() in case
* the child dies and is reaped by another thread.
*
* We only do the memory accounting at this point and
* leave the buffer deallocation and the bts tracer
* release to ptrace_bts_untrace() which will be called
* later on with tasklist_lock held.
*/
release_locked_buffer(child->bts_buffer, child->bts_size);
}
#else
static inline void ptrace_bts_fork(struct task_struct *tsk) {}

View file

@ -1305,5 +1305,6 @@ void vmemmap_populate_print_last(void);
extern void *alloc_locked_buffer(size_t size);
extern void free_locked_buffer(void *buffer, size_t size);
extern void release_locked_buffer(void *buffer, size_t size);
#endif /* __KERNEL__ */
#endif /* _LINUX_MM_H */

View file

@ -657,7 +657,7 @@ void *alloc_locked_buffer(size_t size)
return buffer;
}
void free_locked_buffer(void *buffer, size_t size)
void release_locked_buffer(void *buffer, size_t size)
{
unsigned long pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT;
@ -667,6 +667,11 @@ void free_locked_buffer(void *buffer, size_t size)
current->mm->locked_vm -= pgsz;
up_write(&current->mm->mmap_sem);
}
void free_locked_buffer(void *buffer, size_t size)
{
release_locked_buffer(buffer, size);
kfree(buffer);
}