[Devel] [PATCH rh7 3/3] netfilter: x_tables: avoid stack-out-of-bounds read in xt_copy_counters_from_user

[Andrey Ryabinin]

From: Eric Dumazet <edumazet at google.com>

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 at google.com>
Cc: Willem de Bruijn <willemb at google.com>
Acked-by: Florian Westphal <fw at strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo at netfilter.org>
(cherry picked from commit e466af75c074e76107ae1cd5a2823e9c61894ffb)
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 net/netfilter/x_tables.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 38f6d7106f98..29704d861624 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -928,7 +928,7 @@ 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
@@ -941,9 +941,9 @@ 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;
-- 
2.16.4