linux-kernel - [PATCH 3.16 094/204] netfilter: x_tables: avoid stack-out-of-bounds read in xt_copy_counters_from

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Date:   Thu, 28 Dec 2017 17:05:44 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Willem de Bruijn" <willemb@...gle.com>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Florian Westphal" <fw@...len.de>,
        "Pablo Neira Ayuso" <pablo@...filter.org>
Subject: [PATCH 3.16 094/204] netfilter: x_tables: avoid stack-out-of-bounds
 read in xt_copy_counters_from_user

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.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@...gle.com>
Cc: Willem de Bruijn <willemb@...gle.com>
Acked-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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
@@ -860,7 +860,7 @@ 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
@@ -873,9 +873,9 @@ 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;