[libvirt] [PATCH 14/15] util: maintain caps when running command with uid != 0

[Eric Blake]

On 02/07/2013 02:37 PM, Laine Stump wrote:
> virCommand was previously calling virSetUIDGID() to change the uid and
> gid of the child process, then separately calling
> virSetCapabilities(). This did not work if the desired uid was != 0,
> since a setuid to anything other than 0 normally clears all
> capabilities bits.
> 
> The solution is to use the new virSetUIDGIDWithCaps(), sending it the
> uid, gid, and capabilities bits. This will get the new process setup
> properly.
> 
> Since the static functions virSetCapabilities() and
> virClearCapabilities are no longer called, they have been removed.
> 
> NOTE: When combined with "filecap $path-to-qemu sys_rawio", this patch
> will make CAP_SYS_RAWIO (which is required for passthrough of generic
> scsi commands to a guest - see commits e8daeeb, 177db08, 397e6a7, and
> 74e0349) be retained by qemu when necessary. Apparently that
> capability has been broken for non-root qemu every since it was

s/every/ever/

> originally added.
> ---
>  src/util/vircommand.c | 76 ++++++---------------------------------------------
>  1 file changed, 8 insertions(+), 68 deletions(-)

ACK.


> -# else
> -static int virClearCapabilities(void)
> -{
> -//    VIR_WARN("libcap-ng support not compiled in, unable to clear "
> -//             "capabilities");

Odd that we had commented this out previously.  Should patch 13/15 log
any warnings when we are not preserving/clearing capabilities, rather
than silently ignoring the capability request?

>  
> -    if (cmd->uid > 0 || cmd->gid > 0) {
> -        VIR_DEBUG("Setting child uid:gid to %u:%u", cmd->uid, cmd->gid);
> -        if (virSetUIDGID(cmd->uid, cmd->gid) < 0)
> +    /* The steps above may need todo something privileged, so we delay

As long as you are touching this comment, s/todo/to do/ (but you've
moved it at least twice in this series, so it depends on how much churn
you want on when you finally fix it).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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