addrconf: always initialize sysctl table data

When sysctl performs restrict writes, it allows to write from
a middle position of a sysctl file, which requires us to initialize
the table data before calling proc_dostring() for the write case.

Fixes: 3d1bec99320d ("ipv6: introduce secret_stable to ipv6_devconf")
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 7 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 17f8e7ea133b..1f21087accab 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5369,13 +5369,10 @@ static int addrconf_sysctl_stable_secret(struct ctl_table *ctl, int write,
                 goto out;
         }
 
-        if (!write) {
-                err = snprintf(str, sizeof(str), "%pI6",
-                               &secret->secret);
-                if (err >= sizeof(str)) {
-                        err = -EIO;
-                        goto out;
-                }
+        err = snprintf(str, sizeof(str), "%pI6", &secret->secret);
+        if (err >= sizeof(str)) {
+                err = -EIO;
+                goto out;
         }
 
         err = proc_dostring(&lctl, write, buffer, lenp, ppos);