linux-kernel - [16/27] svcrpc: fix double-free on shutdown of nfsd after changing pool mode

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Message-Id: <20120123234203.025513019@clark.kroah.org>
Date:	Mon, 23 Jan 2012 15:41:02 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, "J. Bruce Fields" <bfields@...hat.com>
Subject: [16/27] svcrpc: fix double-free on shutdown of nfsd after changing pool mode

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

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

From: "J. Bruce Fields" <bfields@...hat.com>

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 file changed, 3 insertions(+)

--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -166,6 +166,7 @@ svc_pool_map_alloc_arrays(struct svc_poo

 fail_free:
 	kfree(m->to_pool);
+	m->to_pool = NULL;
 fail:
 	return -ENOMEM;
 }
@@ -286,7 +287,9 @@ svc_pool_map_put(void)
 	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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