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author | Eric W. Biederman <ebiederm@xmission.com> | 2007-09-13 07:18:57 (GMT) |
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committer | David S. Miller <davem@sunset.davemloft.net> | 2007-10-10 23:49:22 (GMT) |
commit | 077130c0cf7d5ba1992f5b51b96136d7b1c8aad5 (patch) | |
tree | c8fd2622e7d633cc504c7543b55e25bd6d99a2fa /include/net/net_namespace.h | |
parent | 4fabcd7118162e36eea5c53e8895ecc13762bef3 (diff) | |
download | linux-fsl-qoriq-077130c0cf7d5ba1992f5b51b96136d7b1c8aad5.tar.xz |
[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>
Diffstat (limited to 'include/net/net_namespace.h')
-rw-r--r-- | include/net/net_namespace.h | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h index 3081b6e..ac8f830 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)) |