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kern: ether_gen_addr: randomize on default hostuuid, too

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Currently, this will still hash the default (all zero) hostuuid and
potentially arrive at a MAC address that has a high chance of collision
if another interface of the same name appears in the same broadcast
domain on another host without a hostuuid, e.g., some virtual machine
setups.

Instead of using the default hostuuid, just treat it as a failure and
generate a random LA unicast MAC address.

Reviewed by:	bz, gbe, imp, kbowling, kp
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D29788
This commit is contained in:
Kyle Evans 2021-04-15 20:11:35 -05:00
parent e58a65ccda
commit 2d741f33bd
4 changed files with 18 additions and 6 deletions
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5
share/man/man9/ether_gen_addr.9
View file

@ -61,8 +61,9 @@ or on machines that do not use
.Xr loader 8 .
.Pp
.Nm
can fail to derive a MAC address due to memory allocation failure.
In this case, a locally-administered unicast MAC address will be randomly
can fail to derive a MAC address due to memory allocation failure, or because
the hostid has not been populated.
In these cases, a locally-administered unicast MAC address will be randomly
generated and returned via the
.Ar hwaddr
parameter.

1
sys/kern/kern_jail.c
View file

@ -76,7 +76,6 @@ __FBSDID("$FreeBSD$");
#include <security/mac/mac_framework.h>
#define DEFAULT_HOSTUUID "00000000-0000-0000-0000-000000000000"
#define PRISON0_HOSTUUID_MODULE "hostuuid"
MALLOC_DEFINE(M_PRISON, "prison", "Prison structures");

17
sys/net/if_ethersubr.c
View file

@ -1443,6 +1443,11 @@ ether_gen_addr(struct ifnet *ifp, struct ether_addr *hwaddr)
char jailname[MAXHOSTNAMELEN];
getcredhostuuid(curthread->td_ucred, uuid, sizeof(uuid));
if (strncmp(uuid, DEFAULT_HOSTUUID, sizeof(uuid)) == 0) {
/* Fall back to a random mac address. */
goto rando;
}
/* If each (vnet) jail would also have a unique hostuuid this would not
* be necessary. */
getjailname(curthread->td_ucred, jailname, sizeof(jailname));
@ -1450,9 +1455,7 @@ ether_gen_addr(struct ifnet *ifp, struct ether_addr *hwaddr)
jailname);
if (sz < 0) {
/* Fall back to a random mac address. */
arc4rand(hwaddr, sizeof(*hwaddr), 0);
hwaddr->octet[0] = 0x02;
return;
goto rando;
}
SHA1Init(&ctx);
@ -1467,6 +1470,14 @@ ether_gen_addr(struct ifnet *ifp, struct ether_addr *hwaddr)
hwaddr->octet[i] = addr >> ((ETHER_ADDR_LEN - i - 1) * 8) &
0xFF;
}
return;
rando:
arc4rand(hwaddr, sizeof(*hwaddr), 0);
/* Unicast */
hwaddr->octet[0] &= 0xFE;
/* Locally administered. */
hwaddr->octet[0] |= 0x02;
}
DECLARE_MODULE(ether, ether_mod, SI_SUB_INIT_IF, SI_ORDER_ANY);

1
sys/sys/jail.h
View file

@ -140,6 +140,7 @@ MALLOC_DECLARE(M_PRISON);
#include <sys/osd.h>
#define HOSTUUIDLEN 64
#define DEFAULT_HOSTUUID "00000000-0000-0000-0000-000000000000"
#define OSRELEASELEN 32
struct racct;