Patch "scm: fix MSG_CTRUNC setting condition for SO_PASSSEC" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    scm: fix MSG_CTRUNC setting condition for SO_PASSSEC

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     scm-fix-msg_ctrunc-setting-condition-for-so_passsec.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3553e5c35c78a2d528eaa78af46a5f814d986e94
Author: Alexander Mikhalitsyn <alexander@xxxxxxxxxxxxx>
Date:   Mon Mar 13 12:32:11 2023 +0100

    scm: fix MSG_CTRUNC setting condition for SO_PASSSEC
    
    [ Upstream commit a02d83f9947d8f71904eda4de046630c3eb6802c ]
    
    Currently, kernel would set MSG_CTRUNC flag if msg_control buffer
    wasn't provided and SO_PASSCRED was set or if there was pending SCM_RIGHTS.
    
    For some reason we have no corresponding check for SO_PASSSEC.
    
    In the recvmsg(2) doc we have:
           MSG_CTRUNC
                  indicates that some control data was discarded due to lack
                  of space in the buffer for ancillary data.
    
    So, we need to set MSG_CTRUNC flag for all types of SCM.
    
    This change can break applications those don't check MSG_CTRUNC flag.
    
    Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
    Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
    Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
    Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
    Cc: Leon Romanovsky <leon@xxxxxxxxxx>
    Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
    Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
    
    v2:
    - commit message was rewritten according to Eric's suggestion
    Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
    
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/net/scm.h b/include/net/scm.h
index 1ce365f4c2560..585adc1346bd0 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -105,16 +105,27 @@ static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct sc
 		}
 	}
 }
+
+static inline bool scm_has_secdata(struct socket *sock)
+{
+	return test_bit(SOCK_PASSSEC, &sock->flags);
+}
 #else
 static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
 { }
+
+static inline bool scm_has_secdata(struct socket *sock)
+{
+	return false;
+}
 #endif /* CONFIG_SECURITY_NETWORK */
 
 static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
 				struct scm_cookie *scm, int flags)
 {
 	if (!msg->msg_control) {
-		if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp)
+		if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp ||
+		    scm_has_secdata(sock))
 			msg->msg_flags |= MSG_CTRUNC;
 		scm_destroy(scm);
 		return;