On Nov 27, 2012, at 4:31 PM, "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> On Mon, Nov 26, 2012 at 05:51:16PM -0500, J. Bruce Fields wrote:
>> On Mon, Nov 26, 2012 at 05:38:49PM -0500, Chuck Lever wrote:
>>> What exactly is the problem with the current code?
>>>
>>> client_resolve() can return a NULL in some cases. Why is it OK to
>>> pass a NULL "ai" to client_compose() ? Looks like that can result in
>>> a mountd segfault.
>>
>> Bah, I thought I'd checked this and found it was prepared to handle
>> that, but no:
>>
>> client_check->check_wildcard()
>>
>> looks like it can oops.
>
> Right, so the real problem is just that we're skipping the downcall on
> failure instead of responding with a negative cache entry. Thus we're
> leaving the client hanging instead of returning an error.
>
> So, I suppose we should do the below, based on steved's suggestion
> (compiled, otherwise untested).
Thanks, this seems reasonable.
>
> --b.
>
> commit dfb31d861261c8461a2dc4fb7e8823f5169a9079
> Author: J. Bruce Fields <bfields@xxxxxxxxxx>
> Date: Tue Nov 27 16:10:41 2012 -0500
>
> mountd: auth_unix_ip should downcall on error to prevent hangs
>
> Since bf6a4febaa78bf188896b7b5b02c46562dd08b70 "mountd: handle
> allocation failures in auth_unix_ip upcall", a failure to map the
> address of an incoming client to a name could result in a hang.
>
> We should be responding with an error in the case, not just skipping the
> downcall and leaving everybody hanging.
>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
>
> diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
> index e950ec6..c13f305 100644
> --- a/utils/mountd/cache.c
> +++ b/utils/mountd/cache.c
> @@ -109,12 +109,10 @@ static void auth_unix_ip(FILE *f)
> struct addrinfo *ai = NULL;
>
> ai = client_resolve(tmp->ai_addr);
> - if (ai == NULL)
> - goto out;
> - client = client_compose(ai);
> - freeaddrinfo(ai);
> - if (!client)
> - goto out;
> + if (ai) {
> + client = client_compose(ai);
> + freeaddrinfo(ai);
> + }
> }
> qword_print(f, "nfsd");
> qword_print(f, ipaddr);
> @@ -127,7 +125,6 @@ static void auth_unix_ip(FILE *f)
> xlog(D_CALL, "auth_unix_ip: client %p '%s'", client, client?client: "DEFAULT");
>
> free(client);
> -out:
> freeaddrinfo(tmp);
>
> }
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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