netfilter: x_tables: avoid stack-out-of-bounds read in xt_copy_counters_from_user

syzkaller reports an out of bound read in strlcpy(), triggered
by xt_copy_counters_from_user()

Fix this by using memcpy(), then forcing a zero byte at the last position
of the destination, as Florian did for the non COMPAT code.

Fixes: d7591f0c41ce ("netfilter: x_tables: introduce and use xt_copy_counters_from_user")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index c83a3b5e1c6c..d8571f414208 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -892,7 +892,7 @@ void *xt_copy_counters_from_user(const void __user *user, unsigned int len,
                 if (copy_from_user(&compat_tmp, user, sizeof(compat_tmp)) != 0)
                         return ERR_PTR(-EFAULT);
 
-                strlcpy(info->name, compat_tmp.name, sizeof(info->name));
+                memcpy(info->name, compat_tmp.name, sizeof(info->name) - 1);
                 info->num_counters = compat_tmp.num_counters;
                 user += sizeof(compat_tmp);
         } else
@@ -905,9 +905,9 @@ void *xt_copy_counters_from_user(const void __user *user, unsigned int len,
                 if (copy_from_user(info, user, sizeof(*info)) != 0)
                         return ERR_PTR(-EFAULT);
 
-                info->name[sizeof(info->name) - 1] = '\0';
                 user += sizeof(*info);
         }
+        info->name[sizeof(info->name) - 1] = '\0';
 
         size = sizeof(struct xt_counters);
         size *= info->num_counters;