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>

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index c83a3b5e1c6c2a91b713b6681a794bd79ab3fa08..d8571f4142080a3c121fc90f0b52d81ee9df6712 100644 (file)
--- 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;