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 ever since it was
originally added.
This is an interim measure to make sure everything still works in this
order. The next step will be to perform capabilities drop and
setuid/gid as a single operation (which is the only way to keep any
capabilities when switching to a non-root uid).
virCommand gets two new APIs: virCommandSetSELinuxLabel() and
virCommandSetAppArmorProfile(), which both save a copy of a
null-terminated string in the virCommand. During virCommandRun, if the
string is non-NULL and we've been compiled with AppArmor and/or
SELinux security driver support, the appropriate security library
function is called for the child process, using the string that was
previously set. In the case of SELinux, setexeccon_raw() is called,
and for AppArmor, aa_change_profile() is called.
This functionality has been added so that users of virCommand can use
the upcoming virSecurityManagerSetChildProcessLabel() prior to running
a child process, rather than needing to setup a hook function to be
called (and in turn call virSecurityManagerSetProcessLabel()) *during*
the setup of the child process.
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).
All args except "cmd" in the call to virExec are now redundant, since
they can all be found in cmd, so remove the args and reference the
data directly in cmd. One exception to this is that "infd" was being
modified within virExec, and modifying the original in cmd caused make
check failures, so cmd->infd is copied to a local, and the local is
used during virExec().
virExecWithHook is only called from one place, so it always has the
same "hook" function (virHookCommand), and the data sent to that
function is always a virCommandPtr, so eliminate the function and
generic data from the arglist, and replace it with "virCommandPtr
cmd". The call to (hook)(data) is replaced with
"virHookCommand(cmd)". Finally, virExecWithHook is renamed to virExec.
Indentation has been updated only for code that will remain after the
next patch, which will remove all other args to virExec (since they
are now redundant, as they're all members of virCommandPtr).
Currently, if a command wants to do asynchronous IO, a callback
is registered in the libvirtd eventloop to handle writes and
reads. However, there's a race in virCommandWait. The eventloop
may already be executing the callback, while virCommandWait is
mangling internal state of virCommand. To deal with it, we need
to either introduce locking or spawn a separate thread where we
poll() on stdio from child. The former, however, requires to
unlock all mutexes held, as the event loop may execute other
callbacks which tries to lock one of the mutexes, deadlock and
thus never wake us up. So it's safer to spawn a separate thread.
Currently, if we want to feed stdin, or catch stdout or stderr of a
virCommand we have to use virCommandRun(). When using virCommandRunAsync()
we have to register FD handles by hand. This may lead to code duplication.
Hence, introduce an internal API, which does this automatically within
virCommandRunAsync(). The intended usage looks like this:
virCommandPtr cmd = virCommandNew*(...);
char *buf = NULL;
...
virCommandSetOutputBuffer(cmd, &buf);
virCommandDoAsyncIO(cmd);
if (virCommandRunAsync(cmd, NULL) < 0)
goto cleanup;
...
if (virCommandWait(cmd, NULL) < 0)
goto cleanup;
/* @buf now contains @cmd's stdout */
VIR_DEBUG("STDOUT: %s", NULLSTR(buf));
...
cleanup:
VIR_FREE(buf);
virCommandFree(cmd);
Note, that both stdout and stderr buffers may change until virCommandWait()
returns.
