Re: [libvirt] [PATCHv2 04/15] util: add virCommandSetUID and virCommandSetGID
On 02/12/2013 07:16 PM, Eric Blake wrote:
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?
Well, at the bottom of the call chain, all three operations (setuid,
setgid, and set/clear capabilities) have to be done in a single
function, but setting capabilities is necessarily a separate function at
the higher level because you need to call it multiple times to set
multiple capabilities, and it seemed like a natural extension to make
setuid and setgid separate functions at this level too; seems to go
along with the general philosophy in virCommand of having many separate
simple calls, rather than a few really complicated ones.
> @@ -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.