Commit 077130c0 authored by Eric W. Biederman's avatar Eric W. Biederman Committed by David S. Miller

[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: default avatarEric W. Biederman <ebiederm@xmission.com>
Acked-by: default avatarPaul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4fabcd71
......@@ -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,
......
......@@ -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;
......
......@@ -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))
......
......@@ -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;
}
......
......@@ -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;
}
......
......@@ -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;
}
......
......@@ -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;
}
......
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