netfilter: ipt_CLUSTERIP: fix buffer overflow

'buffer' string is copied from userspace.  It is not checked whether it is
zero terminated.  This may lead to overflow inside of simple_strtoul().
Changli Gao suggested to copy not more than user supplied 'size' bytes.

It was introduced before the git epoch.  Files "ipt_CLUSTERIP/*" are
root writable only by default, however, on some setups permissions might be
relaxed to e.g. network admin user.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
index 403ca57f6011..d609ac3cb9a4 100644
--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
@@ -664,8 +664,11 @@ static ssize_t clusterip_proc_write(struct file *file, const char __user *input,
         char buffer[PROC_WRITELEN+1];
         unsigned long nodenum;
 
-        if (copy_from_user(buffer, input, PROC_WRITELEN))
+        if (size > PROC_WRITELEN)
+                return -EIO;
+        if (copy_from_user(buffer, input, size))
                 return -EFAULT;
+        buffer[size] = 0;
 
         if (*buffer == '+') {
                 nodenum = simple_strtoul(buffer+1, NULL, 10);