[PATCH net 1/2] net: bpfilter: restart bpfilter_umh when error occurred

[Taehee Yoo]

When bpfilter error occurred bpfilter_umh will be stopped via __stop_umh().
The bpfilter_umh() couldn't start again because there is no restart
routine.

The section of bpfilter_umh_{start/end} is no longer .init.rodata
because these area should be reused in the restart routine. hence
the section name is changed to .bpfilter_umh.

Test commands:
   $ iptables -vnL
   $ kill -9 <pid of bpfilter_umh>
   $ iptables -vnL
   [  480.045136] bpfilter: write fail -32

   $ iptables -vnL
   iptables v1.8.1 (legacy): can't initialize iptables table `filter': No child 
processes
   Perhaps iptables or your kernel needs to be upgraded.

Then, iptables command is always failed.

Fixes: d2ba09c17a06 ("net: add skeleton of bpfilter kernel module")
Signed-off-by: Taehee Yoo <ap420...@gmail.com>
---
 include/linux/bpfilter.h         |  2 ++
 net/bpfilter/bpfilter_kern.c     | 12 +++++++++++-
 net/bpfilter/bpfilter_umh_blob.S |  2 +-
 net/ipv4/bpfilter/sockopt.c      |  6 +++++-
 4 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpfilter.h b/include/linux/bpfilter.h
index f02cee0225d4..3039361cd65a 100644
--- a/include/linux/bpfilter.h
+++ b/include/linux/bpfilter.h
@@ -12,4 +12,6 @@ int bpfilter_ip_get_sockopt(struct sock *sk, int optname, 
char __user *optval,
 extern int (*bpfilter_process_sockopt)(struct sock *sk, int optname,
                                       char __user *optval,
                                       unsigned int optlen, bool is_set);
+extern int (*bpfilter_start_umh)(void);
+
 #endif
diff --git a/net/bpfilter/bpfilter_kern.c b/net/bpfilter/bpfilter_kern.c
index 7acfc83087d5..7397f5e8da2f 100644
--- a/net/bpfilter/bpfilter_kern.c
+++ b/net/bpfilter/bpfilter_kern.c
@@ -87,7 +87,7 @@ static int __bpfilter_process_sockopt(struct sock *sk, int 
optname,
        return ret;
 }
 
-static int __init load_umh(void)
+int start_umh(void)
 {
        int err;
 
@@ -111,8 +111,18 @@ static int __init load_umh(void)
        return 0;
 }
 
+static int __init load_umh(void)
+{
+       if (IS_ENABLED(CONFIG_INET))
+               bpfilter_start_umh = &start_umh;
+
+       return start_umh();
+}
+
 static void __exit fini_umh(void)
 {
+       if (IS_ENABLED(CONFIG_INET))
+               bpfilter_start_umh = NULL;
        stop_umh();
 }
 module_init(load_umh);
diff --git a/net/bpfilter/bpfilter_umh_blob.S b/net/bpfilter/bpfilter_umh_blob.S
index 40311d10d2f2..7f1c521dcc2f 100644
--- a/net/bpfilter/bpfilter_umh_blob.S
+++ b/net/bpfilter/bpfilter_umh_blob.S
@@ -1,5 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
-       .section .init.rodata, "a"
+       .section .bpfilter_umh, "a"
        .global bpfilter_umh_start
 bpfilter_umh_start:
        .incbin "net/bpfilter/bpfilter_umh"
diff --git a/net/ipv4/bpfilter/sockopt.c b/net/ipv4/bpfilter/sockopt.c
index 5e04ed25bc0e..f7efcff9634d 100644
--- a/net/ipv4/bpfilter/sockopt.c
+++ b/net/ipv4/bpfilter/sockopt.c
@@ -10,6 +10,9 @@ int (*bpfilter_process_sockopt)(struct sock *sk, int optname,
                                unsigned int optlen, bool is_set);
 EXPORT_SYMBOL_GPL(bpfilter_process_sockopt);
 
+int (*bpfilter_start_umh)(void);
+EXPORT_SYMBOL_GPL(bpfilter_start_umh);
+
 static int bpfilter_mbox_request(struct sock *sk, int optname,
                                 char __user *optval,
                                 unsigned int optlen, bool is_set)
@@ -20,7 +23,8 @@ static int bpfilter_mbox_request(struct sock *sk, int optname,
                if (err)
                        return err;
                if (!bpfilter_process_sockopt)
-                       return -ECHILD;
+                       if (!bpfilter_start_umh || bpfilter_start_umh())
+                               return -ECHILD;
        }
        return bpfilter_process_sockopt(sk, optname, optval, optlen, is_set);
 }
-- 
2.17.1