[PATCH 4.14 041/110] net: ipv4: dont allow setting net.ipv4.route.min_pmtu below 68

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

--

From: Sabrina Dubroca 


[ Upstream commit c7272c2f1229125f74f22dcdd59de9bbd804f1c8 ]

According to RFC 1191 sections 3 and 4, ICMP frag-needed messages
indicating an MTU below 68 should be rejected:

A host MUST never reduce its estimate of the Path MTU below 68
octets.

and (talking about ICMP frag-needed's Next-Hop MTU field):

This field will never contain a value less than 68, since every
router "must be able to forward a datagram of 68 octets without
fragmentation".

Furthermore, by letting net.ipv4.route.min_pmtu be set to negative
values, we can end up with a very large PMTU when (-1) is cast into u32.

Let's also make ip_rt_min_pmtu a u32, since it's only ever compared to
unsigned ints.

Reported-by: Jianlin Shi 
Signed-off-by: Sabrina Dubroca 
Reviewed-by: Stefano Brivio 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman 
---
 net/ipv4/route.c |8 ++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -128,10 +128,13 @@ static int ip_rt_redirect_silence __read
 static int ip_rt_error_cost __read_mostly  = HZ;
 static int ip_rt_error_burst __read_mostly = 5 * HZ;
 static int ip_rt_mtu_expires __read_mostly = 10 * 60 * HZ;
-static int ip_rt_min_pmtu __read_mostly= 512 + 20 + 20;
+static u32 ip_rt_min_pmtu __read_mostly= 512 + 20 + 20;
 static int ip_rt_min_advmss __read_mostly  = 256;
 
 static int ip_rt_gc_timeout __read_mostly  = RT_GC_TIMEOUT;
+
+static int ip_min_valid_pmtu __read_mostly = IPV4_MIN_MTU;
+
 /*
  * Interface to generic destination cache.
  */
@@ -2934,7 +2937,8 @@ static struct ctl_table ipv4_route_table
.data   = _rt_min_pmtu,
.maxlen = sizeof(int),
.mode   = 0644,
-   .proc_handler   = proc_dointvec,
+   .proc_handler   = proc_dointvec_minmax,
+   .extra1 = _min_valid_pmtu,
},
{
.procname   = "min_adv_mss",

[PATCH 4.14 041/110] net: ipv4: dont allow setting net.ipv4.route.min_pmtu below 68

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

--

From: Sabrina Dubroca 


[ Upstream commit c7272c2f1229125f74f22dcdd59de9bbd804f1c8 ]

According to RFC 1191 sections 3 and 4, ICMP frag-needed messages
indicating an MTU below 68 should be rejected:

A host MUST never reduce its estimate of the Path MTU below 68
octets.

and (talking about ICMP frag-needed's Next-Hop MTU field):

This field will never contain a value less than 68, since every
router "must be able to forward a datagram of 68 octets without
fragmentation".

Furthermore, by letting net.ipv4.route.min_pmtu be set to negative
values, we can end up with a very large PMTU when (-1) is cast into u32.

Let's also make ip_rt_min_pmtu a u32, since it's only ever compared to
unsigned ints.

Reported-by: Jianlin Shi 
Signed-off-by: Sabrina Dubroca 
Reviewed-by: Stefano Brivio 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman 
---
 net/ipv4/route.c |8 ++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -128,10 +128,13 @@ static int ip_rt_redirect_silence __read
 static int ip_rt_error_cost __read_mostly  = HZ;
 static int ip_rt_error_burst __read_mostly = 5 * HZ;
 static int ip_rt_mtu_expires __read_mostly = 10 * 60 * HZ;
-static int ip_rt_min_pmtu __read_mostly= 512 + 20 + 20;
+static u32 ip_rt_min_pmtu __read_mostly= 512 + 20 + 20;
 static int ip_rt_min_advmss __read_mostly  = 256;
 
 static int ip_rt_gc_timeout __read_mostly  = RT_GC_TIMEOUT;
+
+static int ip_min_valid_pmtu __read_mostly = IPV4_MIN_MTU;
+
 /*
  * Interface to generic destination cache.
  */
@@ -2934,7 +2937,8 @@ static struct ctl_table ipv4_route_table
.data   = _rt_min_pmtu,
.maxlen = sizeof(int),
.mode   = 0644,
-   .proc_handler   = proc_dointvec,
+   .proc_handler   = proc_dointvec_minmax,
+   .extra1 = _min_valid_pmtu,
},
{
.procname   = "min_adv_mss",