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Re: [libvirt] [PATCHv2 04/15] util: add virCommandSetUID and virCommandSetGID



On 02/12/2013 01:15 PM, Laine Stump wrote:
> If a uid and/or gid is specified for a command, it will be set just
> after the user-supplied post-fork "hook" function is called.
> 
> The intent is that this can replace user hook functions that set
> uid/gid. This moves the setting of uid/gid and dropping of
> capabilities closer to each other, which is important since the two
> should really be done at the same time (libcapng provides a single
> function that does both, which we will be unable to use, but want to
> mimic as closely as possible).
> ---
> Change from V1: 
> * only bypass uid/gid setting if they are -1
> * cast -1 to ([gu]id_t) when comparing to a [gu]id_t
> * cast uid and gid to (int) for printing
> 
>  src/libvirt_private.syms |  2 ++
>  src/util/vircommand.c    | 29 +++++++++++++++++++++++++++++
>  src/util/vircommand.h    |  6 +++++-
>  3 files changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> index b9d45a2..511a686 100644
> --- a/src/libvirt_private.syms
> +++ b/src/libvirt_private.syms
> @@ -158,12 +158,14 @@ virCommandRun;
>  virCommandRunAsync;
>  virCommandSetErrorBuffer;
>  virCommandSetErrorFD;
> +virCommandSetGID;
>  virCommandSetInputBuffer;
>  virCommandSetInputFD;
>  virCommandSetOutputBuffer;
>  virCommandSetOutputFD;
>  virCommandSetPidFile;
>  virCommandSetPreExecHook;
> +virCommandSetUID;

Is it common enough to set both gid/uid at once, in order to make this a
single function virCommandSetUIDGID?

> @@ -605,6 +607,13 @@ virExec(virCommandPtr cmd)
>             goto fork_error;
>      }
>  
> +    if (cmd->uid != (uid_t)-1 || cmd->gid != (gid_t)-1) {
> +        VIR_DEBUG("Setting child uid:gid to %d:%d",
> +                  (int)cmd->uid, (int)cmd->gid);
> +        if (virSetUIDGID(cmd->uid, cmd->gid) < 0)

In fact, down at a lower layer in the stack, we pass both ids at once.

Hmm, in the chown() case, doing both at once lets you use one syscall
instead of two; but in the set*id() functions, it's separate syscalls
for uid vs. gid no matter what we do, so I guess it doesn't really
matter whether it is two separate calls or one combined call higher up
in the stack.  But what you have with separate calls works, so I don't
mind whether you keep it as-is, to save the hassle of rippling a
combined call through the rest of the series.

ACK.

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

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