[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@xmission.com>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index 358930a..85cc8e8 100644 (file)
--- 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 (file)
--- 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 3081b6e..ac8f830 100644 (file)
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -46,6 +46,18 @@ 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 d16dcab..666c112 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2464,7 +2464,11 @@ 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 (file)
--- 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 (file)
--- 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 (file)
--- 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;
 }