Re: [Bugme-new] [Bug 10880] New: include/linux/if_addr.h: negative preferred lifetimes of addresses

On Sat,  7 Jun 2008 03:04:43 -0700 (PDT) bugme-daemon@bugzilla.kernel.org wrote:

http://bugzilla.kernel.org/show_bug.cgi?id=10880

           Summary: include/linux/if_addr.h: negative preferred lifetimes of
                    addresses
           Product: Networking
           Version: 2.5
     KernelVersion: 2.6.25.4
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: IPV6
        AssignedTo: yoshfuji@linux-ipv6.org
        ReportedBy: benedikt@gollatz.net


Recently, I noticed that iproute2 would return me preferred lifetimes of IPv6
adresses close to 2^32 on links where prefixes are advertised with a preferred
lifetime of 0. A quick look into the source revealed that the preferred
lifetime is output using a format string containing "%u"; the incriminating
lines being

  struct ifa_cacheinfo *ci = RTA_DATA(rta_tb[IFA_CACHEINFO]);
  char buf[128];
  fprintf(fp, "%s", _SL_);
  [...]
  if (ci->ifa_prefered == INFINITY_LIFE_TIME)
       sprintf(buf+strlen(buf), " preferred_lft forever");
  else
       sprintf(buf+strlen(buf), " preferred_lft %usec",
               ci->ifa_prefered);
  fprintf(fp, "       %s", buf);

When calling iproute2 oftenly shortly after a prefix has been advertised on the
link, one could see that there actually was an integer underflow going on (the
output changed from "0" to "forever" to 2^32-1).

Interestringly, if_addr.h does define ifa_prefered to be a __u32, so iproute2
merely implements the interface. RFC4862 mandates that the preferred lifetime
always is lower than or equal to the valid lifetime, which is also defined to
be a __u32.

I'm certainly no expert in the linux kernel code, but this looks like a bug to
me. Why is ifa_prefered defined to be non-negative?

Benedikt


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