linux-kernel - [PATCH 72/91] svcrpc: fix double-free on shutdown of nfsd after changing pool mode

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Message-Id: <20120205220952.526747546@pcw.home.local>
Date:	Sun, 05 Feb 2012 23:11:01 +0100
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	"J. Bruce Fields" <bfields@...hat.com>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: [PATCH 72/91] svcrpc: fix double-free on shutdown of nfsd after changing pool mode

2.6.27-longterm review patch.  If anyone has any objections, please let us know.

------------------

commit 61c8504c428edcebf23b97775a129c5b393a302b upstream.

The pool_to and to_pool fields of the global svc_pool_map are freed on
shutdown, but are initialized in nfsd startup only in the
SVC_POOL_PERCPU and SVC_POOL_PERNODE cases.

They *are* initialized to zero on kernel startup.  So as long as you use
only SVC_POOL_GLOBAL (the default), this will never be a problem.

You're also OK if you only ever use SVC_POOL_PERCPU or SVC_POOL_PERNODE.

However, the following sequence events leads to a double-free:

	1. set SVC_POOL_PERCPU or SVC_POOL_PERNODE
	2. start nfsd: both fields are initialized.
	3. shutdown nfsd: both fields are freed.
	4. set SVC_POOL_GLOBAL
	5. start nfsd: the fields are left untouched.
	6. shutdown nfsd: now we try to free them again.

Step 4 is actually unnecessary, since (for some bizarre reason), nfsd
automatically resets the pool mode to SVC_POOL_GLOBAL on shutdown.

Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 net/sunrpc/svc.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

Index: longterm-2.6.27/net/sunrpc/svc.c
===================================================================
--- longterm-2.6.27.orig/net/sunrpc/svc.c	2012-02-05 22:34:32.810915144 +0100
+++ longterm-2.6.27/net/sunrpc/svc.c	2012-02-05 22:34:45.104915090 +0100
@@ -163,6 +163,7 @@
 
 fail_free:
 	kfree(m->to_pool);
+	m->to_pool = NULL;
 fail:
 	return -ENOMEM;
 }
@@ -283,7 +284,9 @@
 	if (!--m->count) {
 		m->mode = SVC_POOL_DEFAULT;
 		kfree(m->to_pool);
+		m->to_pool = NULL;
 		kfree(m->pool_to);
+		m->pool_to = NULL;
 		m->npools = 0;
 	}
 


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