[PATCH] proc: optimize proc_check_dentry_visible (5b0c1dd3) · Commits · 戴 / test

The code doesn't need to sleep to when making this check so I can just do the comparison and not worry about the reference counts. TODO: While looking at this I realized that my original cleanup did not push the permission check far enough down into the stack. The call of proc_check_dentry_visible needs to move out of the generic proc readlink/follow link code and into the individual get_link instances. Otherwise the shared resources checks are not quite correct (shared files_struct does not require a shared fs_struct), and there are races with unshare. Signed-off-by:

Eric W. Biederman <ebiederm@xmission.com> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

fs/proc/base.c

+16 −13

Original line number	Diff line number	Diff line
		@@ -1074,24 +1074,27 @@ static int proc_check_dentry_visible(struct inode *inode,
		* namespace, or are simply process local (like pipes).
		*/
		struct task_struct *task;
		struct files_struct task_files, files;
		int error = -EACCES;

		/* See if the the two tasks share a commone set of
		* file descriptors. If so everything is visible.
		*/
		task = get_proc_task(inode);
		if (!task)
		goto out;
		files = get_files_struct(current);
		task_files = get_files_struct(task);
		if (files && task_files && (files == task_files))
		rcu_read_lock();
		task = tref_task(proc_tref(inode));
		if (task) {
		struct files_struct task_files, files;
		/* This test answeres the question:
		* Is there a point in time since we looked up the
		* file descriptor where the two tasks share the
		* same files struct?
		*/
		rmb();
		files = current->files;
		task_files = task->files;
		if (files && (files == task_files))
		error = 0;
		if (task_files)
		put_files_struct(task_files);
		if (files)
		put_files_struct(files);
		put_task_struct(task);
		}
		rcu_read_unlock();
		if (!error)
		goto out;

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