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netns: add and use net_ns_barrier

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Quoting Joe Stringer:
  If a user loads nf_conntrack_ftp, sends FTP traffic through a network
  namespace, destroys that namespace then unloads the FTP helper module,
  then the kernel will crash.

Events that lead to the crash:
1. conntrack is created with ftp helper in netns x
2. This netns is destroyed
3. netns destruction is scheduled
4. netns destruction wq starts, removes netns from global list
5. ftp helper is unloaded, which resets all helpers of the conntracks
via for_each_net()

but because netns is already gone from list the for_each_net() loop
doesn't include it, therefore all of these conntracks are unaffected.

6. helper module unload finishes
7. netns wq invokes destructor for rmmod'ed helper

CC: "Eric W. Biederman" <ebiederm@xmission.com>
Reported-by: Joe Stringer <joe@ovn.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal
2017-05-30 11:38:12 +02:00
committed by Pablo Neira Ayuso
parent 2c41f33c1b
commit 7866cc57b5
3 changed files with 29 additions and 0 deletions
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3
include/net/net_namespace.h
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@@ -158,6 +158,7 @@ extern struct net init_net;
struct net *copy_net_ns(unsigned long flags, struct user_namespace *user_ns,
struct net *old_net);
void net_ns_barrier(void);
#else /* CONFIG_NET_NS */
#include <linux/sched.h>
#include <linux/nsproxy.h>
@@ -168,6 +169,8 @@ static inline struct net *copy_net_ns(unsigned long flags,
return ERR_PTR(-EINVAL);
return old_net;
}
static inline void net_ns_barrier(void) {}
#endif /* CONFIG_NET_NS */