[PATCH 4.2.y-ckt 274/305] addrconf: always initialize sysctl table data

[Kamal Mostafa]

4.2.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: WANG Cong <xiyou.wangcong@xxxxxxxxx>

commit 5449a5ca9bc27dd51a462de7ca0b1cd861cd2bd0 upstream.

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@xxxxxxxxxx>
Acked-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
 net/ipv6/addrconf.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index f4d78a4..d956e30 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5269,13 +5269,10 @@ 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);
-- 
1.9.1