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Message-ID: <m14phzam2l.fsf@ebiederm.dsl.xmission.com>
Date: Wed, 12 Sep 2007 10:24:34 -0600
From: ebiederm@...ssion.com (Eric W. Biederman)
To: David Miller <davem@...emloft.net>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
<netdev@...r.kernel.org>,
Linux Containers <containers@...ts.osdl.org>
Subject: [PATCH] net: Fix race when opening a proc file while a network namespace is exiting.
The problem: proc_net files remember which network namespace the are
against but do not remember hold a reference count (as that would pin
the network namespace). So we currently have a small window where
the reference count on a network namespace may be incremented when opening
a /proc file when it has already gone to zero.
To fix this introduce maybe_get_net and get_proc_net.
maybe_get_net increments the network namespace reference count only if it is
greater then zero, ensuring we don't increment a reference count after it
has gone to zero.
get_proc_net handles all of the magic to go from a proc inode to the network
namespace instance and call maybe_get_net on it.
PROC_NET the old accessor is removed so that we don't get confused and use
the wrong helper function.
Then I fix up the callers to use get_proc_net and handle the case case
where get_proc_net returns NULL. In that case I return -ENXIO because
effectively the network namespace has already gone away so the files
we are trying to access don't exist anymore.
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
---
fs/proc/proc_net.c | 6 ++++++
include/linux/proc_fs.h | 5 +----
include/net/net_namespace.h | 12 ++++++++++++
net/core/dev.c | 6 +++++-
net/core/dev_mcast.c | 6 +++++-
net/netlink/af_netlink.c | 6 +++++-
net/wireless/wext.c | 6 +++++-
7 files changed, 39 insertions(+), 8 deletions(-)
diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index 358930a..85cc8e8 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -51,6 +51,12 @@ void proc_net_remove(struct net *net, const char *name)
}
EXPORT_SYMBOL_GPL(proc_net_remove);
+struct net *get_proc_net(const struct inode *inode)
+{
+ return maybe_get_net(PDE_NET(PDE(inode)));
+}
+EXPORT_SYMBOL_GPL(get_proc_net);
+
static struct proc_dir_entry *proc_net_shadow;
static struct dentry *proc_net_shadow_dentry(struct dentry *parent,
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 5964670..20741f6 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -270,10 +270,7 @@ static inline struct net *PDE_NET(struct proc_dir_entry *pde)
return pde->parent->data;
}
-static inline struct net *PROC_NET(const struct inode *inode)
-{
- return PDE_NET(PDE(inode));
-}
+struct net *get_proc_net(const struct inode *inode);
struct proc_maps_private {
struct pid *pid;
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index fac42db..dda03f3 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -39,6 +39,18 @@ static inline struct net *get_net(struct net *net)
return net;
}
+static inline struct net *maybe_get_net(struct net *net)
+{
+ /* Used when we know struct net exists but we
+ * aren't guaranteed a previous reference count
+ * exists. If the reference count is zero this
+ * function fails and returns NULL.
+ */
+ if (!atomic_inc_not_zero(&net->count))
+ net = NULL;
+ return net;
+}
+
static inline void put_net(struct net *net)
{
if (atomic_dec_and_test(&net->count))
diff --git a/net/core/dev.c b/net/core/dev.c
index a22a95d..f119dc0 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2446,7 +2446,11 @@ static int dev_seq_open(struct inode *inode, struct file *file)
res = seq_open(file, &dev_seq_ops);
if (!res) {
seq = file->private_data;
- seq->private = get_net(PROC_NET(inode));
+ seq->private = get_proc_net(inode);
+ if (!seq->private) {
+ seq_release(inode, file);
+ res = -ENXIO;
+ }
}
return res;
}
diff --git a/net/core/dev_mcast.c b/net/core/dev_mcast.c
index 1c4f619..896b0ca 100644
--- a/net/core/dev_mcast.c
+++ b/net/core/dev_mcast.c
@@ -246,7 +246,11 @@ static int dev_mc_seq_open(struct inode *inode, struct file *file)
res = seq_open(file, &dev_mc_seq_ops);
if (!res) {
seq = file->private_data;
- seq->private = get_net(PROC_NET(inode));
+ seq->private = get_proc_net(inode);
+ if (!seq->private) {
+ seq_release(inode, file);
+ res = -ENXIO;
+ }
}
return res;
}
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 3029f86..dc9f8c2 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1859,7 +1859,11 @@ static int netlink_seq_open(struct inode *inode, struct file *file)
seq = file->private_data;
seq->private = iter;
- iter->net = get_net(PROC_NET(inode));
+ iter->net = get_proc_net(inode);
+ if (!iter->net) {
+ seq_release_private(inode, file);
+ return -ENXIO;
+ }
return 0;
}
diff --git a/net/wireless/wext.c b/net/wireless/wext.c
index e8b3409..85e5f9d 100644
--- a/net/wireless/wext.c
+++ b/net/wireless/wext.c
@@ -678,7 +678,11 @@ static int wireless_seq_open(struct inode *inode, struct file *file)
res = seq_open(file, &wireless_seq_ops);
if (!res) {
seq = file->private_data;
- seq->private = get_net(PROC_NET(inode));
+ seq->private = get_proc_net(inode);
+ if (!seq->private) {
+ seq_release(inode, file);
+ res = -ENXIO;
+ }
}
return res;
}
--
1.5.3.rc6.17.g1911
-
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