[PATCH 4.9 67/70] netfilter: x_tables: avoid stack-out-of-bounds read in xt_copy_counters_from_user

Greg Kroah-Hartman
2018-09-17T22:59:17Z

From: Eric Dumazet <edumazet@google.com>

commit e466af75c074e76107ae1cd5a2823e9c61894ffb upstream.

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>
Cc: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/netfilter/x_tables.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -877,7 +877,7 @@ void *xt_copy_counters_from_user(const v
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
@@ -890,9 +890,9 @@ void *xt_copy_counters_from_user(const v
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;