Subject: [net v3] tcp: Specify cmsgbuf is user pointer for receive zerocopy.

From: Arjun Roy <[email-masked]>
Date: Thu, 6 May 2021 15:35:30 -0700

From: Arjun Roy <[email-masked]>

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 <[email-masked]>
Reviewed-by: Eric Dumazet <[email-masked]>
Cc: Jakub Kicinski <[email-masked]>

---

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(+)

Changelog since v2:
- Updated CC list. Added review-by annotation.

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