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authorEric Dumazet <edumazet@google.com>2013-08-18 19:08:07 -0700
committerDavid S. Miller <davem@davemloft.net>2013-08-20 15:05:04 -0700
commit734d2725db879f3f6fcdc2b1d2a5deae105f5e95 (patch)
tree44648101fe8a2960add4c7d3b690f3fbcaac8841 /net
parent35596b2796713c6a9dc05759837fa9f0e156a200 (diff)
downloadlinux-734d2725db879f3f6fcdc2b1d2a5deae105f5e95.tar.bz2
ipv4: raise IP_MAX_MTU to theoretical limit
As discussed last year [1], there is no compelling reason to limit IPv4 MTU to 0xFFF0, while real limit is 0xFFFF [1] : http://marc.info/?l=linux-netdev&m=135607247609434&w=2 Willem raised this issue again because some of our internal regression tests broke after lo mtu being set to 65536. IP_MTU reports 0xFFF0, and the test attempts to send a RAW datagram of mtu + 1 bytes, expecting the send() to fail, but it does not. Alexey raised interesting points about TCP MSS, that should be addressed in follow-up patches in TCP stack if needed, as someone could also set an odd mtu anyway. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> Cc: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/route.c8
1 files changed, 3 insertions, 5 deletions
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index e805481eff72..727f4365bcdf 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -112,7 +112,8 @@
#define RT_FL_TOS(oldflp4) \
((oldflp4)->flowi4_tos & (IPTOS_RT_MASK | RTO_ONLINK))
-#define IP_MAX_MTU 0xFFF0
+/* IPv4 datagram length is stored into 16bit field (tot_len) */
+#define IP_MAX_MTU 0xFFFF
#define RT_GC_TIMEOUT (300*HZ)
@@ -1227,10 +1228,7 @@ static unsigned int ipv4_mtu(const struct dst_entry *dst)
mtu = 576;
}
- if (mtu > IP_MAX_MTU)
- mtu = IP_MAX_MTU;
-
- return mtu;
+ return min_t(unsigned int, mtu, IP_MAX_MTU);
}
static struct fib_nh_exception *find_exception(struct fib_nh *nh, __be32 daddr)