Add UNIX_DIAG_UID to Netlink UNIX socket diagnostics.

Author: Felipe Gasper <felipe@felipegasper.com>
Date:   Thu May 16 12:16:53 2019 -0500

    Add UNIX_DIAG_UID to Netlink UNIX socket diagnostics.
    
    This adds the ability for Netlink to report a socket’s UID along with the
    other UNIX socket diagnostic information that is already available. This will
    allow diagnostic tools greater insight into which users control which socket.
    
    Signed-off-by: Felipe Gasper <felipe@felipegasper.com>

> On May 16, 2019, at 8:25 PM, Felipe <felipe@felipegasper.com> wrote:
>
> Author: Felipe Gasper <felipe@felipegasper.com>
> Date:   Thu May 16 12:16:53 2019 -0500
>
>    Add UNIX_DIAG_UID to Netlink UNIX socket diagnostics.
>
>    This adds the ability for Netlink to report a socket’s UID along with the
>    other UNIX socket diagnostic information that is already available. This will
>    allow diagnostic tools greater insight into which users control which socket.
>
>    Signed-off-by: Felipe Gasper <felipe@felipegasper.com>
>
> diff --git a/include/uapi/linux/unix_diag.h b/include/uapi/linux/unix_diag.h
> index 5c502fd..a198857 100644
> --- a/include/uapi/linux/unix_diag.h
> +++ b/include/uapi/linux/unix_diag.h
> @@ -20,6 +20,7 @@ struct unix_diag_req {
> #define UDIAG_SHOW_ICONS    0x00000008    /* show pending connections */
> #define UDIAG_SHOW_RQLEN    0x00000010    /* show skb receive queue len */
> #define UDIAG_SHOW_MEMINFO    0x00000020    /* show memory info of a socket */
> +#define UDIAG_SHOW_UID        0x00000040    /* show socket's UID */
>
> struct unix_diag_msg {
>    __u8    udiag_family;
> @@ -40,6 +41,7 @@ enum {
>    UNIX_DIAG_RQLEN,
>    UNIX_DIAG_MEMINFO,
>    UNIX_DIAG_SHUTDOWN,
> +    UNIX_DIAG_UID,
>
>    __UNIX_DIAG_MAX,
> };
> diff --git a/net/unix/diag.c b/net/unix/diag.c
> index 3183d9b..011f56c 100644
> --- a/net/unix/diag.c
> +++ b/net/unix/diag.c
> @@ -110,6 +110,11 @@ static int sk_diag_show_rqlen(struct sock *sk, struct sk_buff *nlskb)
>    return nla_put(nlskb, UNIX_DIAG_RQLEN, sizeof(rql), &rql);
> }
>
> +static int sk_diag_dump_uid(struct sock *sk, struct sk_buff *nlskb)
> +{
> +    return nla_put(nlskb, UNIX_DIAG_UID, sizeof(kuid_t), &(sk->sk_uid));

That type is called *k* uid_t because it’s internal to the kernel. You
probably want from_kuid_munged(), which will fix it up for an
appropriate userns.  Presumably you want sk’s netns’s userns.

> On May 17, 2019, at 12:59 AM, Andy Lutomirski <luto@kernel.org> wrote:
> 
>> On May 16, 2019, at 8:25 PM, Felipe <felipe@felipegasper.com> wrote:
>> 
>> Author: Felipe Gasper <felipe@felipegasper.com>
>> Date:   Thu May 16 12:16:53 2019 -0500
>> 
>>   Add UNIX_DIAG_UID to Netlink UNIX socket diagnostics.
>> 
>>   This adds the ability for Netlink to report a socket’s UID along with the
>>   other UNIX socket diagnostic information that is already available. This will
>>   allow diagnostic tools greater insight into which users control which socket.
>> 
>>   Signed-off-by: Felipe Gasper <felipe@felipegasper.com>
>> 
>> diff --git a/include/uapi/linux/unix_diag.h b/include/uapi/linux/unix_diag.h
>> index 5c502fd..a198857 100644
>> --- a/include/uapi/linux/unix_diag.h
>> +++ b/include/uapi/linux/unix_diag.h
>> @@ -20,6 +20,7 @@ struct unix_diag_req {
>> #define UDIAG_SHOW_ICONS    0x00000008    /* show pending connections */
>> #define UDIAG_SHOW_RQLEN    0x00000010    /* show skb receive queue len */
>> #define UDIAG_SHOW_MEMINFO    0x00000020    /* show memory info of a socket */
>> +#define UDIAG_SHOW_UID        0x00000040    /* show socket's UID */
>> 
>> struct unix_diag_msg {
>>   __u8    udiag_family;
>> @@ -40,6 +41,7 @@ enum {
>>   UNIX_DIAG_RQLEN,
>>   UNIX_DIAG_MEMINFO,
>>   UNIX_DIAG_SHUTDOWN,
>> +    UNIX_DIAG_UID,
>> 
>>   __UNIX_DIAG_MAX,
>> };
>> diff --git a/net/unix/diag.c b/net/unix/diag.c
>> index 3183d9b..011f56c 100644
>> --- a/net/unix/diag.c
>> +++ b/net/unix/diag.c
>> @@ -110,6 +110,11 @@ static int sk_diag_show_rqlen(struct sock *sk, struct sk_buff *nlskb)
>>   return nla_put(nlskb, UNIX_DIAG_RQLEN, sizeof(rql), &rql);
>> }
>> 
>> +static int sk_diag_dump_uid(struct sock *sk, struct sk_buff *nlskb)
>> +{
>> +    return nla_put(nlskb, UNIX_DIAG_UID, sizeof(kuid_t), &(sk->sk_uid));
> 
> That type is called *k* uid_t because it’s internal to the kernel. You
> probably want from_kuid_munged(), which will fix it up for an
> appropriate userns.  Presumably you want sk’s netns’s userns.

Thank you for pointing this out.

Would it suffice to get the userns as: “sk_user_ns(sk)”?

Or would it be better to pass struct netlink_callback *cb from unix_diag_dump() to sk_diag_dump() to sk_diag_fill(), then to the new function to add the UID?

cheers,
-Felipe Gasper