Re: [PATCH net] netfilter: xt_hashlimit: do not allow empty names

On Sun, Jan 28, 2018 at 09:54:05AM -0800, Eric Dumazet wrote:

On Sun, 2018-01-28 at 07:41 -0800, Eric Dumazet wrote:

quoted

From: Eric Dumazet <edumazet@google.com>

Syzbot reported a WARN() in proc_create_data() [1]

Issue here is that xt_hashlimit does not check that user space provided
an empty table name.

quoted

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <redacted>
---
 net/netfilter/xt_hashlimit.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 5da8746f7b88ff4c9446f256e542e823a6a561b0..eae732e013df92a364b500645360d4606c283a75 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c

@@ -894,6 +894,8 @@ static int hashlimit_mt_check_common(const struct xt_mtchk_param *par,
 			return -ERANGE;
 	}
 
+	if (!name[0])
+		return -EINVAL;
 	mutex_lock(&hashlimit_mutex);
 	*hinfo = htable_find_get(net, name, par->family);
 	if (*hinfo == NULL) {

I wonder if we should also check if name includes a '/' ?

if (!name[0] || strchr(name, '/'))
    return -EINVAL;

We can probably add our own variant of dev_valid_name?

bool nf_valid_name(const char *name, size_t len)
{
        if (*name == '\0')
                return false;
        if (strlen(name) >= len)
                return false;
        if (!strcmp(name, ".") || !strcmp(name, ".."))
                return false;

        while (*name) {
                if (*name == '/' || *name == ':' || isspace(*name))
                        return false;
                name++;
        }
        return true;
}

Or place this in the core, something like:

bool net_valid_name(const char *name, size_t len)
{
        ...
}

then use it from dev_valid_name()

bool dev_valid_name(const char *name)
{
        return net_valid_name(name, IFNAMSIZ);
}

@Eric, I can give it a shot here to this, just let me know. Thanks!