linux-kernel - [34/35] udp/recvmsg: Clear MSG_TRUNC flag when starting over for a new packet

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Message-Id: <20110708225122.081079051@clark.kroah.org>
Date:	Fri, 08 Jul 2011 15:50:23 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Xufeng Zhang <xufeng.zhang@...driver.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [34/35] udp/recvmsg: Clear MSG_TRUNC flag when starting over for a new packet

2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------


From: Xufeng Zhang <xufeng.zhang@...driver.com>

[ Upstream commit 9cfaa8def1c795a512bc04f2aec333b03724ca2e ]

Consider this scenario: When the size of the first received udp packet
is bigger than the receive buffer, MSG_TRUNC bit is set in msg->msg_flags.
However, if checksum error happens and this is a blocking socket, it will
goto try_again loop to receive the next packet.  But if the size of the
next udp packet is smaller than receive buffer, MSG_TRUNC flag should not
be set, but because MSG_TRUNC bit is not cleared in msg->msg_flags before
receive the next packet, MSG_TRUNC is still set, which is wrong.

Fix this problem by clearing MSG_TRUNC flag when starting over for a
new packet.

Signed-off-by: Xufeng Zhang <xufeng.zhang@...driver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 net/ipv4/udp.c |    3 +++
 net/ipv6/udp.c |    3 +++
 2 files changed, 6 insertions(+)

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1011,6 +1011,9 @@ csum_copy_err:
 
 	if (noblock)
 		return -EAGAIN;
+
+	/* starting over for a new packet */
+	msg->msg_flags &= ~MSG_TRUNC;
 	goto try_again;
 }
 
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -306,6 +306,9 @@ csum_copy_err:
 
 	if (noblock)
 		return -EAGAIN;
+
+	/* starting over for a new packet */
+	msg->msg_flags &= ~MSG_TRUNC;
 	goto try_again;
 }
 


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