[xen staging] tools/hotplug: validate mtu read from xenstore against RFC 791 minimum

[patchbot@xxxxxxx]

commit 7d6c3308cb6eab5ec3742d24b3d05c934498bcb5
Author:     James Dingwall <james@xxxxxxxxxxxxxx>
AuthorDate: Fri Aug 14 07:03:51 2026 +0100
Commit:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
CommitDate: Mon Oct 12 17:31:39 2026 +0200

    tools/hotplug: validate mtu read from xenstore against RFC 791 minimum
    
    RFC 791 sets the minimum acceptable mtu to 68:
    
        Every internet module must be able to forward a datagram of 68
        octets without further fragmentation.  This is because an internet
        header may be up to 60 octets, and the minimum fragment is 8 octets.
    
    In the Linux kernel source:
    
    include/net/ip.h:#define IPV4_MIN_MTU           68              /* RFC 791 
*/
    
    While there is no reason to expect a value <68 to be read from xenstore or
    from the bridge make the value test require a number >= this minimum.
    
    Signed-off-by: James Dingwall <james@xxxxxxxxxxxxxx>
    Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 tools/hotplug/Linux/xen-network-common.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/hotplug/Linux/xen-network-common.sh 
b/tools/hotplug/Linux/xen-network-common.sh
index f83eeef030..344730cb42 100644
--- a/tools/hotplug/Linux/xen-network-common.sh
+++ b/tools/hotplug/Linux/xen-network-common.sh
@@ -167,7 +167,7 @@ set_mtu () {
             log debug "$bridge MTU is $mtu"
         fi
     fi
-    if [ -n "$mtu" ] && [ "$mtu" -gt 0 ]
+    if [ -n "$mtu" ] && [ "$mtu" -ge 68 ]
     then
         log debug "setting $dev MTU to $mtu"
         ip link set dev ${dev} mtu ${mtu} || :
--
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