[PATCH] Fix memory overwriting issue when copy an address to user space

[lebon zhou]

On Mon, Jul 20, 2020 at 11:12 PM David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> From: lebon zhou
> > Sent: 20 July 2020 05:35
> > To: davem@xxxxxxxxxxxxx; kuba@xxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx
> > Subject: [PATCH] Fix memory overwriting issue when copy an address to user space
> >
> > When application provided buffer size less than sockaddr_storage, then
> > kernel will overwrite some memory area which may cause memory corruption,
> > e.g.: in recvmsg case, let msg_name=malloc(8) and msg_namelen=8, then
> > usually application can call recvmsg successful but actually application
> > memory get corrupted.
>
> Where?
> The copy_to_user() uses the short length provided by the user.
> There is even a comment saying that if the address is truncated
> the length returned to the user is the full length.
>
> Maybe the application is reusing the msg without re-initialising
> it properly.

It is not related with copy_to_user(), it is about move_addr_to_user()
implementation itself,
there is comment /*After copying the data up to the limit the user
specifies...*/, but the fact
is when (ulen < klen), this function will copy more content to user
buffer over than user
specifies in @ulen, this will cause the user buffer to corrupt, this
patch fixes this issue.