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nscd on VE [message #26259]

Sat, 19 January 2008 03:17

edel
Messages: 3
Registered: January 2008
Location: Naga City, Philippines

Junior Member

hello great people, in this great society Wink

i have problem running nscd on top of cos ve. from the logfile, it says "30624: Failed to drop capabilities", so i thought i have to enable some caps to run nscd.

here's the relevant info from strace:

Quote:

...
chmod("/var/run/nscd/socket", 0666) = 0
listen(12, 128) = 0
getuid32() = 0
prctl(0x8, 0x1, 0x8c42050, 0xa84f63, 0x8c43258) = 0
capset(0x19980330, 0, {CAP_SETGID|CAP_SETUID|0x20000000, CAP_SETGID|CAP_SETUID|0x20000000, 0}) = -1 EPERM (Operation not permitted)
write(3, "30490: Failed to drop capabiliti"..., 35) = 35
write(2, "nscd: ", 6) = 6
write(2, "cap_set_proc failed", 19) = 19
write(2, "\n", 1) = 1
exit_group(1) = ?

i did try:
vzctl set 1502 --capability setuid:on --save
vzctl set 1502 --capability setgid:on --save
...and reboot.

but it does not succed. i also tried enabling all but setpcap but to no avail still nscd failed to start.

thanks in advance.

--edel

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Re: nscd on VE [message #26494 is a reply to message #26259]

Fri, 25 January 2008 05:16

edel
Messages: 3
Registered: January 2008
Location: Naga City, Philippines

Junior Member

hi,

anyone can help me here? thank you.

--edel

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Re: nscd on VE [message #26830 is a reply to message #26494]

Sat, 02 February 2008 13:25

maratrus
Messages: 1495
Registered: August 2007
Location: Moscow

Senior Member

Hi,

I'm very sorry for delay.

As we can see from strace output setuid and setgid capabilities are not sufficient. We need also CAP_AUDIT_WRITE.

From src/include/linux/capability.h (openvz kernel tree) inside VE we should to set SETVEID capability and "man vzctl" allows us to do this. I tried this but suddenly found that this capability was not actually set. The reason is in kernel's do_env_create() function which is called when we start our VPS. It displaces setveid capability otherwise this VPS becomes the serious hole in security.

So I can suggest you two ways:
1. If it is possible you can use the elder version of nscd. I noticed that it doesn't try to set this capabilities. (I experimented with VPS based on Fedora 4 ).
2. You can compile nscd by yourself. We easily can find the relevant piece of code and can try to comment unnecessary string.

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Re: nscd on VE [message #26839 is a reply to message #26830]

Sat, 02 February 2008 23:59

edel
Messages: 3
Registered: January 2008
Location: Naga City, Philippines

Junior Member

hello maratrus,

thank you very much for the reply.

i was already thnking of recompiling nscd before, however i couldnt find the source for centos5. and honestly, i didnt tried hard enough. since it's a nss, im thinking its part of glibc. not sure. maybe, when i have the time, i'll look into it.

i also tried setting setting up nsscache[1], but didnt get it to work.

for now, here's my workaround (for the benefit of others):

1. on HN, setup nss_ldap and nscd as usual
2. HN's /var/run/nscd is on tmpfs (1mb)
3. HN's /var/db/nscd is on 10mb loopback-mounted image
4. mount (--bind) HN's /var/{run,db}/nscd to /vz/root/${VEID}/var/{run,db}/nscd (via $VEID.mount)

reason for #2/3 is that i dont want to give HN's /var partition open/fully accessible to VEs.

and it appears working.

i got this idea from the mysql/shared hosting form the openvz wiki.

openvz is great!

thanks.

--edel

[1] http://code.google.com/p/nsscache/

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