[PATCH 10/12] netfilter: x_tables: avoid stack-out-of-bounds read in xt_copy_counters_from_user

[Pablo Neira Ayuso]

From: Eric Dumazet <eduma...@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 <eduma...@google.com>
Cc: Willem de Bruijn <will...@google.com>
Acked-by: Florian Westphal <f...@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.org>
---
 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 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;
-- 
2.1.4

--
To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html