From: Eric W. Biederman Date: Thu, 13 Sep 2007 07:18:57 +0000 (+0200) Subject: [NET]: Fix race when opening a proc file while a network namespace is exiting. X-Git-Tag: v2.6.24-rc1~1454^2~675 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=077130c0cf7d5ba1992f5b51b96136d7b1c8aad5;p=linux-2.6 [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 Acked-by: Paul E. McKenney Signed-off-by: David S. Miller --- diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c index 358930a314..85cc8e8bb8 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 59646705f1..20741f668f 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 3081b6ed35..ac8f830409 100644 --- 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 d16dcab49c..666c112efb 100644 --- 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 1c4f619845..896b0ca5ae 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 3029f865cd..dc9f8c2ab1 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 e8b3409d6c..85e5f9dd0d 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; }