[PATCH] [94/99] udp/recvmsg: Clear MSG_TRUNC flag when starting over for a new packet

[Andi Kleen]

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

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

From: Xufeng Zhang <xufeng.zhang@xxxxxxxxxxxxx>

[ 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@xxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>

---
 net/ipv4/udp.c |    3 +++
 net/ipv6/udp.c |    3 +++
 2 files changed, 6 insertions(+)

Index: linux-2.6.35.y/net/ipv4/udp.c
===================================================================
--- linux-2.6.35.y.orig/net/ipv4/udp.c
+++ linux-2.6.35.y/net/ipv4/udp.c
@@ -1206,6 +1206,9 @@ csum_copy_err:
 
 	if (noblock)
 		return -EAGAIN;
+
+	/* starting over for a new packet */
+	msg->msg_flags &= ~MSG_TRUNC;
 	goto try_again;
 }
 
Index: linux-2.6.35.y/net/ipv6/udp.c
===================================================================
--- linux-2.6.35.y.orig/net/ipv6/udp.c
+++ linux-2.6.35.y/net/ipv6/udp.c
@@ -447,6 +447,9 @@ 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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