netdev - v2 [Patch 1/1] [BUG-FIX] udplite: Avoid u16 checksum coverage wrap-around

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Date:	Mon, 21 Jul 2008 11:04:09 +0100
From:	Gerrit Renker <gerrit@....abdn.ac.uk>
To:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: v2 [Patch 1/1] [BUG-FIX] udplite: Avoid u16 checksum coverage
	wrap-around

Dave, can you please have a look at the patch below?

As per earlier request, the default behaviour of rounding small setsockopt
values up to the minimum of 8 has not been changed.

The upshot is that the API now makes it impossible to set an illegal value.
The result has been tested and was found to work.

>>>>>>>>>>>>>>>>>>>>>>>> Patch v2 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
udplite: Protection against coverage value wrap-around

This patch clamps the cscov setsockopt values to a maximum of 0xFFFF.

Setsockopt values greater than 0xffff can cause an unwanted wrap-around.
Further, IPv6 jumbograms are not supported (RFC 3838, 3.5), so that values
greater than 0xffff are not even useful.

Further changes: fixed a typo in the documentation.

Signed-off-by: Gerrit Renker <gerrit@....abdn.ac.uk>
---
 Documentation/networking/udplite.txt |    2 +-
 net/ipv4/udp.c                       |    4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1325,6 +1325,8 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
 			return -ENOPROTOOPT;
 		if (val != 0 && val < 8) /* Illegal coverage: use default (8) */
 			val = 8;
+		else if (val > USHORT_MAX)
+			val = USHORT_MAX;
 		up->pcslen = val;
 		up->pcflag |= UDPLITE_SEND_CC;
 		break;
@@ -1337,6 +1339,8 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
 			return -ENOPROTOOPT;
 		if (val != 0 && val < 8) /* Avoid silly minimal values.       */
 			val = 8;
+		else if (val > USHORT_MAX)
+			val = USHORT_MAX;
 		up->pcrlen = val;
 		up->pcflag |= UDPLITE_RECV_CC;
 		break;
--- a/Documentation/networking/udplite.txt
+++ b/Documentation/networking/udplite.txt
@@ -148,7 +148,7 @@
         getsockopt(sockfd, SOL_SOCKET, SO_NO_CHECK, &value, ...);
 
   is meaningless (as in TCP). Packets with a zero checksum field are
-  illegal (cf. RFC 3828, sec. 3.1) will be silently discarded.
+  illegal (cf. RFC 3828, sec. 3.1) and will be silently discarded.
 
   4) Fragmentation
 
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