Re: [PATCH v2] net: don't unconditionally copy_from_user a struct ifreq for socket ioctls

1 Sep 2021


      On Wed, 1 Sep 2021 08:22:42 +0000 David Laight wrote:
...
From: Jakub Kicinski
...
Sent: 31 August 2021 17:30
On Thu, 26 Aug 2021 12:46:01 -0700 Peter Collingbourne wrote:
...
@@ -3306,6 +3308,8 @@ static int compat_ifr_data_ioctl(struct net *net, unsigned int cmd,
   struct ifreq ifreq;
   u32 data32;

if (!is_socket_ioctl_cmd(cmd))
return -ENOTTY;

if (copy_from_user(ifreq.ifr_name, u_ifreq32->ifr_name, IFNAMSIZ))
return -EFAULT;
if (get_user(data32, &u_ifreq32->ifr_data))

Hi Peter, when resolving the net -> net-next merge conflict I couldn't
figure out why this chunk is needed. It seems all callers of
compat_ifr_data_ioctl() already made sure it's a socket IOCTL.
Please double check my resolution (tip of net-next) and if this is
indeed unnecessary perhaps send a cleanup? Thanks!
To stop the copy_from_user() faulting when the user buffer
isn't long enough.
In particular for iasatty() on arm with tagged pointers.
Let me rephrase. is_socket_ioctl_cmd() is always true here. There were
only two callers, both check cmd is of specific, "sockety" type.

    