git: 2d741f33bd07 - main - kern: ether_gen_addr: randomize on default hostuuid, too

[Ronald Klop]

Hi,

Wouldn't it be user friendly to tell why the MAC is random? Something like this.

 if (strncmp(uuid, DEFAULT_HOSTUUID, sizeof(uuid)) == 0) {
      printf("No /etc/hostuuid found. Fall back to a random mac address.");
      goto rando;
 }

I know it would save me a lot of time if I would encounter this case.
Plus the message is only printed once on boot.

Regards,
Ronald.

 
Van: Kyle Evans <kevans at FreeBSD.org>
Datum: woensdag, 2 juni 2021 05:59
Aan: src-committers at FreeBSD.org, dev-commits-src-all at FreeBSD.org, dev-commits-src-main at FreeBSD.org
Onderwerp: git: 2d741f33bd07 - main - kern: ether_gen_addr: randomize on default hostuuid, too
> 
> The branch main has been updated by kevans:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=2d741f33bd07bf94a59635db3c7b9e070a8a6e55
> 
> commit 2d741f33bd07bf94a59635db3c7b9e070a8a6e55
> Author:     Kyle Evans <kevans at FreeBSD.org>
> AuthorDate: 2021-04-16 01:11:35 +0000
> Commit:     Kyle Evans <kevans at FreeBSD.org>
> CommitDate: 2021-06-02 03:59:21 +0000
> 
>     kern: ether_gen_addr: randomize on default hostuuid, too
>     
>     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
> ---
>  share/man/man9/ether_gen_addr.9 |  5 +++--
>  sys/kern/kern_jail.c            |  1 -
>  sys/net/if_ethersubr.c          | 17 ++++++++++++++---
>  sys/sys/jail.h                  |  1 +
>  4 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/share/man/man9/ether_gen_addr.9 b/share/man/man9/ether_gen_addr.9
> index 1b98a841736d..f69cb199e2c3 100644
> --- a/share/man/man9/ether_gen_addr.9
> +++ b/share/man/man9/ether_gen_addr.9
> @@ -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.
> diff --git a/sys/kern/kern_jail.c b/sys/kern/kern_jail.c
> index 303e31490eb1..9784f3bfc23b 100644
> --- a/sys/kern/kern_jail.c
> +++ b/sys/kern/kern_jail.c
> @@ -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");
> diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
> index 01c2d2f7b3e8..7eb46df8281a 100644
> --- a/sys/net/if_ethersubr.c
> +++ b/sys/net/if_ethersubr.c
> @@ -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);
> diff --git a/sys/sys/jail.h b/sys/sys/jail.h
> index c9d4c65e4d9e..76ed377e3f06 100644
> --- a/sys/sys/jail.h
> +++ b/sys/sys/jail.h
> @@ -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;
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