[net v2] tcp: Specify cmsgbuf is user pointer for receive zerocopy.

[net v2] tcp: Specify cmsgbuf is user pointer for receive zerocopy.

[Arjun Roy]

From: Arjun Roy <arjunroy@google.com>

A prior change (1f466e1f15cf) introduces separate handling for
->msg_control depending on whether the pointer is a kernel or user
pointer. However, while tcp receive zerocopy is using this field, it
is not properly annotating that the buffer in this case is a user
pointer. This can cause faults when the improper mechanism is used
within put_cmsg().

This patch simply annotates tcp receive zerocopy's use as explicitly
being a user pointer.

Fixes: 7eeba1706eba ("tcp: Add receive timestamp support for receive zerocopy.")
Signed-off-by: Arjun Roy <arjunroy@google.com>
---

Changelog since v1:
- Updated "Fixes" tag and commit message to properly account for which
  commit introduced buggy behaviour.

 net/ipv4/tcp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e14fd0c50c10..f1c1f9e3de72 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2039,6 +2039,7 @@ static void tcp_zc_finalize_rx_tstamp(struct sock *sk,
 		(__kernel_size_t)zc->msg_controllen;
 	cmsg_dummy.msg_flags = in_compat_syscall()
 		? MSG_CMSG_COMPAT : 0;
+	cmsg_dummy.msg_control_is_user = true;
 	zc->msg_flags = 0;
 	if (zc->msg_control == msg_control_addr &&
 	    zc->msg_controllen == cmsg_dummy.msg_controllen) {
-- 
2.31.1.607.g51e8a6a459-goog

Re: [net v2] tcp: Specify cmsgbuf is user pointer for receive zerocopy.

[Eric Dumazet]

On Thu, May 6, 2021 at 9:06 PM Arjun Roy <arjunroy.kdev@gmail.com> wrote:
>
> From: Arjun Roy <arjunroy@google.com>
>
> A prior change (1f466e1f15cf) introduces separate handling for
> ->msg_control depending on whether the pointer is a kernel or user
> pointer. However, while tcp receive zerocopy is using this field, it
> is not properly annotating that the buffer in this case is a user
> pointer. This can cause faults when the improper mechanism is used
> within put_cmsg().
>
> This patch simply annotates tcp receive zerocopy's use as explicitly
> being a user pointer.
>
> Fixes: 7eeba1706eba ("tcp: Add receive timestamp support for receive zerocopy.")
> Signed-off-by: Arjun Roy <arjunroy@google.com>

Reviewed-by: Eric Dumazet <edumazet@google.com>


> ---
>
> Changelog since v1:
> - Updated "Fixes" tag and commit message to properly account for which
>   commit introduced buggy behaviour.
>
>  net/ipv4/tcp.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index e14fd0c50c10..f1c1f9e3de72 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2039,6 +2039,7 @@ static void tcp_zc_finalize_rx_tstamp(struct sock *sk,
>                 (__kernel_size_t)zc->msg_controllen;
>         cmsg_dummy.msg_flags = in_compat_syscall()
>                 ? MSG_CMSG_COMPAT : 0;
> +       cmsg_dummy.msg_control_is_user = true;
>         zc->msg_flags = 0;
>         if (zc->msg_control == msg_control_addr &&
>             zc->msg_controllen == cmsg_dummy.msg_controllen) {
> --
> 2.31.1.607.g51e8a6a459-goog
>