Ran into an interesting problem with an in-house program here, that I helped
fix, but was wondering if anyone's seen this before and especially if anyone
has a link to where this might be explained officially on the net. I did
searches and didn't find anything.
Problem was a program that would run fine on a amd64 host if you logged in, but
if you ran on the same host via LSF (Load Sharing Facility.. batch job system)
it would fail. We finally tracked it down to a problem with the value from a
getenv call.. which ltrace showed:
9271 getlogin() = NULL
9271 getenv("USER") = "mmarion"
9271 getenv("USER") = "mmarion"
9271 fprintf(0x00585950, "By user %s \n",
"EOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOFEOF"...
<unfinished ...>
9271 --- SIGSEGV (Segmentation fault) ---
9271 +++ killed by SIGSEGV +++
You can see that getenv("USER") returned a valid answer, but the pointer's value
was then immediately changed to tons of EOF.. which I _think_ is on-purpose to
get poeple to stop using getenv, since you could easily overload the values.
I was able to replace the getenv calls with getpwid(getuid()) and it works like
a charm. But.. like I said, I'd love to see a page on the web that spells out
this deliberate change.
Oh, and the difference between the lsf run and the logged-in one is that even if
you just start a remote shell using lsf, you're not in the utmp file, and the
getenv call seems (in strace output) to look in there to verify if you're
locally logged-in or not.. when when not, that's when the change to the EOF's
happens. To help stop remote root exploits I think.
You can see my fix works:
old:
fprintf(log_file, "By user %s \n", getenv("USER"));
mine:
fprintf(log_file, "By user %s \n", getpwuid(getuid())->pw_name);
ltrace:
15441 getuid() = 32836
15441 getpwuid(32836, 0x7fbfffdd70, 0, 0x2a956f91d9, 0xfefeffffffffffff) =
0x2a958891c0
15441 fprintf(0x00502a00, "By user %s \n", "mmarion") = 17
BTW, my C fu is _really_ weak.. but I slog by like this from time to time. So
no picking on me. :P
--
Mike Marion-Unix SysAdmin/Staff Engineer-http://www.miguelito.org
Marge: "Homer, sitting that close to the TV can't be good for you."
Homer: "Talking while the TV's on can't be good for you!"
==> Simpsons
--
[email protected]
http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
