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netfilter: x_tables: avoid stack-out-of-bounds read in xt_copy_counters_from_user

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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: d7591f0c41 ("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>
This commit is contained in:
Eric Dumazet 2017-10-05 02:50:07 -07:00 committed by Pablo Neira Ayuso
parent 5f9bfe0ef6
commit e466af75c0
1 changed files with 2 additions and 2 deletions
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4
net/netfilter/x_tables.c
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@ -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;