Messages in this thread | | | Date | Sun, 18 Dec 2011 19:17:02 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/2] ptrace: add ability to attach a file descriptor to another task |
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On 12/16, Andrew Vagin wrote: > > Signed-off-by: Andrew Vagin <avagin@openvz.org>
Nice changelog ;)
I agree with Tejun, this doesn't look like the good idea to me...
As for the patch itself,
> @@ -826,6 +827,32 @@ int ptrace_request(struct task_struct *child, long request, > break; > } > #endif > + case PTRACE_DUPFD: > + { > + struct file *file = fget_raw(data); > + ret = -EBADF; > + > + if (!file) > + break; > + > + task_lock(child); > + if (!child->files) > + goto out_getfd; > + > + ret = alloc_task_fd(child, 0, 0);
alloc_fdtable() does kmalloc(GFP_KERNEL)/vmalloc(), not good under spin_lock().
> + if (ret < 0) { > + fput(file);
We can't do this under task_lock() too.
A tracer's sub-thread (or any CLONE_FILES task) can close this file, it is possible that we have the last reference.
Probably, instead of the new *_task_* helpers, you can add alloc_file_fd/fd_files_install which take the result of get_files_struct() as the additional argument. This way you can avoid task_lock().
Oleg.
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