linux-kernel - [PATCH 6/9] procfs: add pid_seq_private struct to handle /proc/<pid>/{stat|stack}

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Date:	Mon, 26 May 2014 14:27:27 +0100
From:	Djalal Harouni <tixxdz@...ndz.org>
To:	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...capital.net>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org,
	Djalal Harouni <tixxdz@...ndz.org>
Subject: [PATCH 6/9] procfs: add pid_seq_private struct to handle /proc/<pid>/{stat|stack}

This patch is preparation to handle sensitive ONE entries:
/proc/<pid>/stat
/proc/<pid>/stack

These files use sequence iterators and we want to keep that logic, and
their internal handler semantics.

The sequence iterators stock the inode in the seq_file->private field,
so in order to keep the semantic and to make the cached permission
checks available during ->read(), we add the 'pid_seq_private' struct
that contains both the inode and the cached permission. It will be the
one referenced in the seq_file->private.

This way the internal handlers of /proc/<pid>/{stat|stack} wont change.

Signed-off-by: Djalal Harouni <tixxdz@...ndz.org>
---
 fs/proc/internal.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index f5c452c..f28e4f01 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -78,6 +78,17 @@ struct proc_inode {
 	struct inode vfs_inode;
 };
 
+/*
+ * Struct used by some /proc/<pid>/$entries that use sequence
+ * iterators.
+ * This struct will be saved in seq_file->private so seq handlers
+ * can access the inode and the cached permission checks of ->open().
+ */
+struct pid_seq_private {
+	int permitted;
+	struct inode *inode;
+};
+
 typedef int (*proc_read_fn_t)(char *page,
 			      struct task_struct *task, int permitted);
 
-- 
1.7.11.7

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