not indicated. the way we use it is basically like
stat, to check that a file exists / is a file.
just err the fuck out
nuance: SETLK is non-blocking (no wait).
we should loop on SETLKW, but we don't use that.
in this codebase, we use SETLK for locking a
tmpfile, but because of race conditions and
wanting to make another file quickly, we just
try again with a newly generated name, with a
certain number of retries, so we justt use SETLK
Signed-off-by: Leah Rowe <leah@libreboot.org>
call it rw_exact, so that it's closer to
the name rw. it matches naming more closely;
the alternative was to call rw rw_file
but read/write can handle more than just files!
Signed-off-by: Leah Rowe <leah@libreboot.org>
even with a timer, it's possible that on a buggy system,
we may keep writing even though the outcome is zero. if
a system comes back with zero bytes written, that is a
fatal bug and we should stop.
Signed-off-by: Leah Rowe <leah@libreboot.org>
i wasn't using strict mode enough in make:
make strict
now it compiles cleanly. mostly removing
unused variables, fixing implicit conversions,
etc.
Signed-off-by: Leah Rowe <leah@libreboot.org>
but i can't write a generic function for this,
because fcntl is a variadic function, so wrapping
cannot be done cleanly.
Signed-off-by: Leah Rowe <leah@libreboot.org>
where possible, try not to clobber sys errno. override
it only when relatively safe.
also: when a syscall succeeds, it may set errno. this
is rare, but permitted (nothing specified against it
in specs, and the specs say that errno is undefined
on success).
i'm not libc, but i'm wrapping around it, so i need
to be careful in how i handle the errno value.
also:
i removed the requirement for directories to be
executable, in mkhtemp.c, because this isn't required
and will only break certain setups.
in world_writeable and sticky, i made the checks stricter:
the faccessat check was being skipped on some paths, so
i've closed that loophole now.
i also generally cleaned up some code, as part of the errno
handling refactoring, where it made sense to do so, plus a
few other bits of code cleanup.
Signed-off-by: Leah Rowe <leah@libreboot.org>
the portable version was written for fun, but
it's bloat, and makes the code hard to read.
every unix since about 2005 has these functions.
Signed-off-by: Leah Rowe <leah@libreboot.org>
remove close_warn and close_no_err
make close_on_eintr a void, and abort
on error instead of returning -1.
a failed file closure is a world-ending
event. burn accordingly.
Signed-off-by: Leah Rowe <leah@libreboot.org>
i now use a singleton hook function per program:
nvmutil, mkhtemp and lottery
call this at the startup of your program:
(void) errhook(exit_cleanup);
then provide that function. make it static,
so that each program has its own version.
if you're writing a program that handles lots
of files for example, and you want to do certain
cleanup on exit (including error exit), this can
be quite useful.
Signed-off-by: Leah Rowe <leah@libreboot.org>
This will also be used in lbmk itself at some point,
which currently just uses regular mktemp, for tmpdir
handling during the build process.
Renamed util/nvmutil to util/libreboot-utils, which
now contains two tools. The new tool, mkhtemp, is a
hardened implementation of mktemp, which nvmutil
also uses now. Still experimental, but good enough
for nvmutil.
Mkhtemp attempts to provide TOCTOU resistance on
Linux, by using modern features in Linux such as
Openat2 (syscall) with O_EXCL and O_TMPFILE,
and many various security checks e.g.
inode/dev during creation. Checks are done constantly,
to try to detect race conditions. The code is very
strict about things like sticky bits in world writeable
directories, also ownership (it can be made to bar even
root access on files and directories it doesn't own).
It's a security-first implementation of mktemp, likely
even more secure than the OpenBSD mkstemp, but more
auditing and testing is needed - more features are
also planned, including a compatibility mode to make
it also work like traditional mktemp/mkstemp. The
intention, once this becomes stable, is that it will
become a modern drop-in replacement for mkstemp on
Linux and BSD systems.
Some legacy code has been removed, and in general
cleaned up. I wrote mkhtemp for nvmutil, as part of
its atomic write behaviour, but mktemp was the last
remaining liability, so I rewrote that too!
Docs/manpage/website will be made for mkhtemp once
the code is mature.
Other changes have also been made. This is from another
experimental branch of Libreboot, that I'm pushing
early. For example, nvmutil's state machine has been
tidied up, moving more logic back into main.
Mktemp is historically prone to race conditions,
e.g. symlink attacks, directory replacement, remounting
during operation, all sorts of things. Mkhtemp has
been written to solve, or otherwise mitigate, that
problem. Mkhtemp is currently experimental and will
require a major cleanup at some point, but it
already works well enough, and you can in fact use
it; at this time, the -d, -p and -q flags are
supported, and you can add a custom template at
the end, e.g.
mkhtemp -p test -d
Eventually, I will make this have complete parity
with the GNU and BSD implementations, so that it is
fully useable on existing setups, while optionally
providing the hardening as well.
A lot of code has also been tidied up. I didn't
track the changes I made with this one, because
it was a major re-write of nvmutil; it is now
libreboot-utils, and I will continue to write
more programs in here over time. It's basically
now a bunch of hardened wrappers around various
libc functions, e.g. there is also a secure I/O
wrapper for read/write.
There is a custom randomisation function, rlong,
which simply uses arc4random or getrandom, on
BSD and Linux respectively. Efforts are made to
make it as reliable as possible, to the extent
that it never returns with failure; in the unlikely
event that it fails, it aborts. It also sleeps
between failure, to mitigate certain DoS attacks.
You can just go in util/libreboot-utils and
type make, then you will have the nvmutil and
mkhtemp binaries, which you can just use. It
all works. Everything was massively rewritten.
Signed-off-by: Leah Rowe <leah@libreboot.org>
Leah Rowe