[PATCH] proc: optimize proc_check_dentry_visible
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>
diff --git a/fs/proc/base.c b/fs/proc/base.c
index c7f8554..f0db7f6 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1074,24 +1074,27 @@
* 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))
- error = 0;
- if (task_files)
- put_files_struct(task_files);
- if (files)
- put_files_struct(files);
- put_task_struct(task);
+ 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;
+ }
+ rcu_read_unlock();
if (!error)
goto out;