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https://github.com/systemd/systemd/pull/2508#issuecomment-190901170
Maybe fixes https://bugzilla.redhat.com/show_bug.cgi?id=1308771.
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Fixes fall-out from 8b3aa503c171acdb9ec63484a8c50e2680d31e79.
Fixes: #2635
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This should be handled fine now by .dir-locals.el, so need to carry that
stuff in every file.
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fds will also be closed during manager cleanup in run, leading
to an error when we try to close them again. It is now possible
to "leak" the fds on error, but it's an unlikely event and we
will exit immediately anyway.
Fixes #2418.
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Little change in practice, because the program will exit soon
afterwards, but the standard style of closing all fds is now followed.
Also gets rid of gcc warning about fd_ctrl and fd_uevent being
unitialized.
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Otherwise emacs wants to use 2-space indentation and other
attrocities.
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GLIB has recently started to officially support the gcc cleanup
attribute in its public API, hence let's do the same for our APIs.
With this patch we'll define an xyz_unrefp() call for each public
xyz_unref() call, to make it easy to use inside a
__attribute__((cleanup())) expression. Then, all code is ported over to
make use of this.
The new calls are also documented in the man pages, with examples how to
use them (well, I only added docs where the _unref() call itself already
had docs, and the examples, only cover sd_bus_unrefp() and
sd_event_unrefp()).
This also renames sd_lldp_free() to sd_lldp_unref(), since that's how we
tend to call our destructors these days.
Note that this defines no public macro that wraps gcc's attribute and
makes it easier to use. While I think it's our duty in the library to
make our stuff easy to use, I figure it's not our duty to make gcc's own
features easy to use on its own. Most likely, client code which wants to
make use of this should define its own:
#define _cleanup_(function) __attribute__((cleanup(function)))
Or similar, to make the gcc feature easier to use.
Making this logic public has the benefit that we can remove three header
files whose only purpose was to define these functions internally.
See #2008.
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Our functions return negative error codes.
Do not rely on errno being set after calling our own functions.
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There are more than enough to deserve their own .c file, hence move them
over.
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string-util.[ch]
There are more than enough calls doing string manipulations to deserve
its own files, hence do something about it.
This patch also sorts the #include blocks of all files that needed to be
updated, according to the sorting suggestions from CODING_STYLE. Since
pretty much every file needs our string manipulation functions this
effectively means that most files have sorted #include blocks now.
Also touches a few unrelated include files.
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Patch via coccinelle.
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The recent cgroup-rework changed the error code for un-mounted cgroupfs to
ENOEXEC. Make sure udev ignores it just like ENOENT and does not spill
warnings on the screen.
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Previously, if the event loop never ran before sd_event_now() would
fail. With this change it will instead fall back to invoking now(). This
way, the function cannot fail anymore, except for programming error when
invoking it with wrong parameters.
This takes into account the fact that many callers did not handle the
error condition correctly, and if the callers did, then they kept simply
invoking now() as fall back on their own. Hence let's shorten the code
using this call, and make things more robust, and let's just fall back
to now() internally.
Whether now() is used or the cache timestamp may still be detected via
the return value of sd_event_now(). If > 0 is returned, then the fall
back to now() was used, if == 0 is returned, then the cached value was
returned.
This patch also simplifies many of the invocations of sd_event_now():
the manual fall back to now() can be removed. Also, in cases where the
call is invoked withing void functions we can now protect the invocation
via assert_se(), acknowledging the fact that the call cannot fail
anymore except for programming errors with the parameters.
This change is inspired by #841.
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udev: fix parameter process
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This way it does not need distinct string literals and it also preserves
the "rd." prefix.
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Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1245293
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The latest consolidation cleanup of write_string_file() revealed some users
of that helper which should have used write_string_file_no_create() in the
past but didn't. Basically, all existing users that write to files in /sys
and /proc should not expect to write to a file which is not yet existant.
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Merge write_string_file(), write_string_file_no_create() and
write_string_file_atomic() into write_string_file() and provide a flags mask
that allows combinations of atomic writing, newline appending and automatic
file creation. Change all users accordingly.
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udev: destroy manager before cleaning environment
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Due to our _cleanup_ usage for the udev manager, it will be destroyed
after the "exit:" label has finished. Therefore, it is the last
destruction done in main(). This has two side-effects:
- mac_selinux is destroyed before the udev manager is, possible causing
use-after-free if the manager-cleanup accesses selinux data
- log_close() is called *before* the manager is destroyed, possibly
re-opening the log if you use --debug (and thus not re-applying the
--debug option)
Avoid this by moving the manager-handling into a new function called
run(). This function will be left before we enter the "exit:" label in
main(), hence, the manager object will be destroyed early.
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https://github.com/systemd/systemd/issues/462
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Fixes CID#1297430.
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This is expected on non-systemd systems, so just log it at debug level.
This fixes issue #309.
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Leftover from 6af5e6a4c918a68b196a04346732e094e5373a36
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This is essentially a revert of 5c67cf2 and fixes issue #190.
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Make sure we never close fds before we drop their related event-source.
This will cause horrible disruptions if the fd-num is re-used by someone
else. Under normal conditions, this should not cause any problems as the
close() will drop the fd from the epoll-set automatically. However, this
changes if you have any child processes with a copy of that fd.
This fixes issue #163.
Background:
If you create an epoll-set via epoll_create() (lets call it 'EFD')
you can add file-descriptors to it to watch for events. Whenever
you call EPOLL_CTL_ADD on a file-descriptor you want to watch, the
kernel looks up the attached "struct file" pointer, that this FD
refers to. This combination of the FD-number and the "struct file"
pointer is used as key to link it into the epoll-set (EFD).
This means, if you duplicate your file-descriptor, you can watch
this file-descriptor, too (because the duplicate will have a
different FD-number, hence, the combination of FD-number and
"struct file" is different as before).
If you want to stop watching an FD, you use EPOLL_CTL_DEL and pass
the FD to the kernel. The kernel again looks up your
file-descriptor in your FD-table to find the linked "struct file".
This FD-number and "struct file" combination is then dropped from
the epoll-set (EFD).
Last, but not least: If you close a file-descriptor that is linked
to an epoll-set, the kernel does *NOTHING* regarding the
epoll-set. This is a vital observation! Because this means, your
epoll_wait() calls will still return the metadata you used to
watch/subscribe your file-descriptor to events.
There is one exception to this rule: If the file-descriptor that
you just close()ed was the last FD that referred to the underlying
"struct file", then _all_ epoll-set watches/subscriptions are
destroyed. Hence, if you never dup()ed your FD, then a simple
close() will also unsubscribe it from any epoll-set.
With this in mind, lets look at fork():
Assume you have an epoll-set (EFD) and a bunch of FDs
subscribed to events on that EFD. If you now call fork(),
the new process gets a copy of your file-descriptor table.
This means, the whole table is copied and the "struct
file" reference of each FD is increased by 1. It is
important to notice that the FD-numbers in the child are
exactly the same as in the parent (eg., FD #5 in the child
refers to the same "struct file" as FD #5 in the parent).
This means, if the child calls EPOLL_CTL_DEL on an FD, the
kernel will look up the linked "struct file" and drop the
FD-number and "struct file" combination from the epoll-set
(EFD). However, this will effectively drop the
subscription that was installed by the parent.
To sum up: even though the child gets a duplicate of the
EFD and all FDs, the subscriptions in the EFD are *NOT*
duplicated!
Now, with this in mind, lets look at what udevd does:
Udevd has a bunch of file-descriptors that it watches in its
sd-event main-loop. Whenever a uevent is received, the event is
dispatched on its workers. If no suitable worker is present, a new
worker is fork()ed to handle the event. Inside of this worker, we
try to free all resources we inherited. However, the fork() call
is done from a call-stack that is never rewinded. Therefore, this
call stack might own references that it drops once it is left.
Those references we cannot deduce from the fork()'ed process;
effectively causing us to leak objects in the worker (eg., the
call to sd_event_dispatch() that dispatched our uevent owns a
reference to the sd_event object it used; and drops it again once
the function is left).
(Another example is udev_monitor_ref() for each 'worker' that is
also inherited by all children; thus keeping the udev-monitor and
the uevent-fd alive in all children (which is the real cause for
bug #163))
(The extreme variant is sd_event_source_unref(), which explicitly
keeps event-sources alive, if they're currently dispatched,
knowing that the dispatcher will free the event once done. But
if the dispatcher is in the parent, the child will never ever
free that object, thus leaking it)
This is usually not an issue. However, if such an object has a
file-descriptor embedded, this FD is left open and never closed in
the child.
In manager_exit(), if we now destroy an object (i.e., close its embedded
file-descriptor) before we destroy its related sd_event_source, then
sd-event will not be able to drop the FD from the epoll-set (EFD). This
is, because the FD is no longer valid at the time we call EPOLL_CTL_DEL.
Hence, the kernel cannot figure out the linked "struct file" and thus
cannot remove the FD-number plus "struct file" combination; effectively
leaving the subscription in the epoll-set.
Since we leak the uevent-fd in the children, they retain a copy of the FD
pointing to the same "struct file". Thus, the EFD-subscription are not
automatically removed by close() (as described above). Therefore, the main
daemon will still get its metadata back on epoll_watch() whenever an event
occurs (even though it already freed the metadata). This then causes the
free-after-use bug described in #163.
This patch fixes the order in which we destruct objects and related
sd-event-sources. Some open questions remain:
* Why does source_io_unregister() not warn on EPOLL_CTL_DEL failures?
This really needs to be turned into an assert_return().
* udevd really should not leak file-descriptors into its children. Fixing
this would *not* have prevented this bug, though (since the child-setup
is still async).
It's non-trivial to fix this, though. The stack-context of the caller
cannot be rewinded, so we cannot figure out temporary refs. Maybe it's
time to exec() the udev-workers?
* Why does the kernel not copy FD-subscriptions across fork()?
Or at least drop subscriptions if you close() your FD (it uses the
FD-number as key, so it better subscribe to it)?
Or it better used
FD+"struct file_table*"+"struct file*"
as key to not allow the childen to share the subscription table..
*sigh*
Seems like we have to live with that API forever.
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This ports a lot of manual code over to sigprocmask_many() and friends.
Also, we now consistly check for sigprocmask() failures with
assert_se(), since the call cannot realistically fail unless there's a
programming error.
Also encloses a few sd_event_add_signal() calls with (void) when we
ignore the return values for it knowingly.
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It's only marginally shorter then the usual for() loop, but certainly
more readable.
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Now that listen_fds() have been split out, we can safely move the allocation
of the manager object after doing the forking (the fork is done to notify legcay
init-systems that the fds are ready).
Subsequently, we can merge manager_listen() back into managre_new().
This entails a minor behaviour change: the application of permissions to
static device nodes now happens after the fork (but still before notifying
systemd about being ready).
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This will simply silently fail on non-systemd systems, so there is no reason
to make it conditional.
Also make it clear that we notify systemd about being ready as the last step
before starting the event loop, whereas the forking might need to happen
earlier.
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This will allow us in a follow-up commit to listen to fds before forking and
still allocate the manager only after the fork.
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Hide the differenec in listen_fds, by simply opening the fds
here in case they are not passed in.
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This should have no behavioural change, but it is odd to tie the cgroup cleaning to
whether or not we are passed sockets.
The point really is if we are guaranteed to be in a dedicated cgroup, so instead
check for our parent being PID1 (we already implicitly only do this on systemd
systems).
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If they are passed from PID1 this is not necessary.
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We used to block all signals, and restore the original signal mask before exec'ing
external processes.
Now we just block the signals we care about and unconditionally unblock all signals
before exec'ing.
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Mostly for documentation purposes.
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The communication channels must all be opened before forknig in daemon mode,
or we cannot guarantee that udevadm will work correctly as soon as udevd is
started.
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