[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/net/core/dev.c b/net/core/dev.c
index d16dcab..666c112 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2464,7 +2464,11 @@
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;
}