net: socket: NULL ptr deref in sendmsg

2014-07-26 2:15 GMT+04:00 Hannes Frederic Sowa <hannes@stressinduktion.org>:
>
> Thanks for looking at this! I certainly have overlooked this case.
>
> I wonder, if we allow sendto with valid NULL pointer and positive
> msg_namelen to work, why don't we do the same for recvmsg, as in
> replacing the VERIFY_WRITE case non-null check with an
> access_ok(VERIFY_WRITE, ...) check? We can even get rid of the check
> because recvmsg will do it nonetheless when copying the sockaddrs to
> user space. So kern_msg->msg_name can always be set to kern_address.
>

recvmsg's man page are pretty clear about that:

     "If the application does not need to
       know the source address, msg_name can be specified as NULL"

I think we shouldn't change current recvmsg behavior, this could break
some crappy
userpace that doesn't set msg_namelen to zero.


> Otherwise I would just set msg_namelen = 0, too, and just not handle
> passed in NULL pointers to sockaddrs.
>

I like that, how about such chage:

                        namep = (void __user __force *) m->msg_name;
@@ -48,10 +48,10 @@ int verify_iovec(struct msghdr *m, struct iovec
*iov, struct sockaddr_storage *a
                        if (err < 0)
                                return err;
                }
-               if (m->msg_name)
-                       m->msg_name = address;
+               m->msg_name = address;
        } else {
                m->msg_name = NULL;
+               m->msg_namelen = 0;
        }

        size = m->msg_iovlen * sizeof(struct iovec);

On Sa, 2014-07-26 at 19:48 +0400, Andrey Ryabinin wrote:
> 2014-07-26 2:15 GMT+04:00 Hannes Frederic Sowa <hannes@stressinduktion.org>:
> > Otherwise I would just set msg_namelen = 0, too, and just not handle
> > passed in NULL pointers to sockaddrs.
> >
> 
> I like that, how about such chage:
> 
> diff --git a/net/compat.c b/net/compat.c
> index 9a76eaf..bc8aeef 100644
> --- a/net/compat.c
> +++ b/net/compat.c
> @@ -85,7 +85,7 @@ int verify_compat_iovec(struct msghdr *kern_msg,
> struct iovec *kern_iov,
>  {
>         int tot_len;
> 
> -       if (kern_msg->msg_namelen) {
> +       if (kern_msg->msg_name && kern_msg->msg_namelen) {
>                 if (mode == VERIFY_READ) {
>                         int err = move_addr_to_kernel(kern_msg->msg_name,
>                                                       kern_msg->msg_namelen,
> @@ -93,10 +93,11 @@ int verify_compat_iovec(struct msghdr *kern_msg,
> struct iovec *kern_iov,
>                         if (err < 0)
>                                 return err;
>                 }
> -               if (kern_msg->msg_name)
> -                       kern_msg->msg_name = kern_address;
> -       } else
> +               kern_msg->msg_name = kern_address;
> +       } else {
>                 kern_msg->msg_name = NULL;
> +               kern_msg->msg_namelen = 0;
> +       }
> 
>         tot_len = iov_from_user_compat_to_kern(kern_iov,
>                                           (struct compat_iovec __user
> *)kern_msg->msg_iov,
> diff --git a/net/core/iovec.c b/net/core/iovec.c
> index 827dd6b..e1ec45a 100644
> --- a/net/core/iovec.c
> +++ b/net/core/iovec.c
> @@ -39,7 +39,7 @@ int verify_iovec(struct msghdr *m, struct iovec
> *iov, struct sockaddr_storage *a
>  {
>         int size, ct, err;
> 
> -       if (m->msg_namelen) {
> +       if (m->msg_name && m->msg_namelen) {
>                 if (mode == VERIFY_READ) {
>                         void __user *namep;
>                         namep = (void __user __force *) m->msg_name;
> @@ -48,10 +48,10 @@ int verify_iovec(struct msghdr *m, struct iovec
> *iov, struct sockaddr_storage *a
>                         if (err < 0)
>                                 return err;
>                 }
> -               if (m->msg_name)
> -                       m->msg_name = address;
> +               m->msg_name = address;
>         } else {
>                 m->msg_name = NULL;
> +               m->msg_namelen = 0;
>         }
> 
>         size = m->msg_iovlen * sizeof(struct iovec);
> 
> 

LGTM! Can you send a patch?

Thanks,
Hannes


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From: Hannes Frederic Sowa <hannes@stressinduktion.org>
Date: Sat, 26 Jul 2014 17:54:40 +0200

> On Sa, 2014-07-26 at 19:48 +0400, Andrey Ryabinin wrote:
>> 2014-07-26 2:15 GMT+04:00 Hannes Frederic Sowa <hannes@stressinduktion.org>:
>> > Otherwise I would just set msg_namelen = 0, too, and just not handle
>> > passed in NULL pointers to sockaddrs.
>> >
>> 
>> I like that, how about such chage:
 ...
> LGTM! Can you send a patch?

I definitely agree that we should treat NULL as no address specified.
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