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authorNeil Horman <nhorman@tuxdriver.com>2007-09-11 11:28:26 +0200
committerDavid S. Miller <davem@davemloft.net>2007-09-11 11:28:26 +0200
commit16fcec35e7d7c4faaa4709f6434a4a25b06d25e3 (patch)
tree5febf4d688f2c32ed55e02bc20246388b74d85e4 /include
parent0fb96701376874c9f1f80322f89a5bf4457c709f (diff)
downloadlinux-linaro-16fcec35e7d7c4faaa4709f6434a4a25b06d25e3.tar.gz
[NETFILTER]: Fix/improve deadlock condition on module removal netfilter
So I've had a deadlock reported to me. I've found that the sequence of events goes like this: 1) process A (modprobe) runs to remove ip_tables.ko 2) process B (iptables-restore) runs and calls setsockopt on a netfilter socket, increasing the ip_tables socket_ops use count 3) process A acquires a file lock on the file ip_tables.ko, calls remove_module in the kernel, which in turn executes the ip_tables module cleanup routine, which calls nf_unregister_sockopt 4) nf_unregister_sockopt, seeing that the use count is non-zero, puts the calling process into uninterruptible sleep, expecting the process using the socket option code to wake it up when it exits the kernel 4) the user of the socket option code (process B) in do_ipt_get_ctl, calls ipt_find_table_lock, which in this case calls request_module to load ip_tables_nat.ko 5) request_module forks a copy of modprobe (process C) to load the module and blocks until modprobe exits. 6) Process C. forked by request_module process the dependencies of ip_tables_nat.ko, of which ip_tables.ko is one. 7) Process C attempts to lock the request module and all its dependencies, it blocks when it attempts to lock ip_tables.ko (which was previously locked in step 3) Theres not really any great permanent solution to this that I can see, but I've developed a two part solution that corrects the problem Part 1) Modifies the nf_sockopt registration code so that, instead of using a use counter internal to the nf_sockopt_ops structure, we instead use a pointer to the registering modules owner to do module reference counting when nf_sockopt calls a modules set/get routine. This prevents the deadlock by preventing set 4 from happening. Part 2) Enhances the modprobe utilty so that by default it preforms non-blocking remove operations (the same way rmmod does), and add an option to explicity request blocking operation. So if you select blocking operation in modprobe you can still cause the above deadlock, but only if you explicity try (and since root can do any old stupid thing it would like.... :) ). Signed-off-by: Neil Horman <nhorman@tuxdriver.com> Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include')
-rw-r--r--include/linux/netfilter.h5
1 files changed, 2 insertions, 3 deletions
diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index 0eed0b7ab2d..1dd075eda59 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -88,9 +88,8 @@ struct nf_sockopt_ops
int (*compat_get)(struct sock *sk, int optval,
void __user *user, int *len);
- /* Number of users inside set() or get(). */
- unsigned int use;
- struct task_struct *cleanup_task;
+ /* Use the module struct to lock set/get code in place */
+ struct module *owner;
};
/* Each queued (to userspace) skbuff has one of these. */