Use INTERNAL_SYSCALL_CALL instead of INLINE_SYSCALL_CALL. This
requires emulate the semantic for hurd call (so __arc4random_buf
uses the fallback).
Checked on x86_64-linux-gnu.
Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Rather than buffering 16 MiB of entropy in userspace (by way of
chacha20), simply call getrandom() every time.
This approach is doubtlessly slower, for now, but trying to prematurely
optimize arc4random appears to be leading toward all sorts of nasty
properties and gotchas. Instead, this patch takes a much more
conservative approach. The interface is added as a basic loop wrapper
around getrandom(), and then later, the kernel and libc together can
work together on optimizing that.
This prevents numerous issues in which userspace is unaware of when it
really must throw away its buffer, since we avoid buffering all
together. Future improvements may include userspace learning more from
the kernel about when to do that, which might make these sorts of
chacha20-based optimizations more possible. The current heuristic of 16
MiB is meaningless garbage that doesn't correspond to anything the
kernel might know about. So for now, let's just do something
conservative that we know is correct and won't lead to cryptographic
issues for users of this function.
This patch might be considered along the lines of, "optimization is the
root of all evil," in that the much more complex implementation it
replaces moves too fast without considering security implications,
whereas the incremental approach done here is a much safer way of going
about things. Once this lands, we can take our time in optimizing this
properly using new interplay between the kernel and userspace.
getrandom(0) is used, since that's the one that ensures the bytes
returned are cryptographically secure. But on systems without it, we
fallback to using /dev/urandom. This is unfortunate because it means
opening a file descriptor, but there's not much of a choice. Secondly,
as part of the fallback, in order to get more or less the same
properties of getrandom(0), we poll on /dev/random, and if the poll
succeeds at least once, then we assume the RNG is initialized. This is a
rough approximation, as the ancient "non-blocking pool" initialized
after the "blocking pool", not before, and it may not port back to all
ancient kernels, though it does to all kernels supported by glibc
(≥3.2), so generally it's the best approximation we can do.
The motivation for including arc4random, in the first place, is to have
source-level compatibility with existing code. That means this patch
doesn't attempt to litigate the interface itself. It does, however,
choose a conservative approach for implementing it.
Cc: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Cristian Rodríguez <crrodriguez@opensuse.org>
Cc: Paul Eggert <eggert@cs.ucla.edu>
Cc: Mark Harris <mark.hsj@gmail.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
The implementation is based on scalar Chacha20 with per-thread cache.
It uses getrandom or /dev/urandom as fallback to get the initial entropy,
and reseeds the internal state on every 16MB of consumed buffer.
To improve performance and lower memory consumption the per-thread cache
is allocated lazily on first arc4random functions call, and if the
memory allocation fails getentropy or /dev/urandom is used as fallback.
The cache is also cleared on thread exit iff it was initialized (so if
arc4random is not called it is not touched).
Although it is lock-free, arc4random is still not async-signal-safe
(the per thread state is not updated atomically).
The ChaCha20 implementation is based on RFC8439 [1], omitting the final
XOR of the keystream with the plaintext because the plaintext is a
stream of zeros. This strategy is similar to what OpenBSD arc4random
does.
The arc4random_uniform is based on previous work by Florian Weimer,
where the algorithm is based on Jérémie Lumbroso paper Optimal Discrete
Uniform Generation from Coin Flips, and Applications (2013) [2], who
credits Donald E. Knuth and Andrew C. Yao, The complexity of nonuniform
random number generation (1976), for solving the general case.
The main advantage of this method is the that the unit of randomness is not
the uniform random variable (uint32_t), but a random bit. It optimizes the
internal buffer sampling by initially consuming a 32-bit random variable
and then sampling byte per byte. Depending of the upper bound requested,
it might lead to better CPU utilization.
Checked on x86_64-linux-gnu, aarch64-linux, and powerpc64le-linux-gnu.
Co-authored-by: Florian Weimer <fweimer@redhat.com>
Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>
[1] https://datatracker.ietf.org/doc/html/rfc8439
[2] https://arxiv.org/pdf/1304.1916.pdf
I used these shell commands:
../glibc/scripts/update-copyrights $PWD/../gnulib/build-aux/update-copyright
(cd ../glibc && git commit -am"[this commit message]")
and then ignored the output, which consisted lines saying "FOO: warning:
copyright statement not found" for each of 7061 files FOO.
I then removed trailing white space from math/tgmath.h,
support/tst-support-open-dev-null-range.c, and
sysdeps/x86_64/multiarch/strlen-vec.S, to work around the following
obscure pre-commit check failure diagnostics from Savannah. I don't
know why I run into these diagnostics whereas others evidently do not.
remote: *** 912-#endif
remote: *** 913:
remote: *** 914-
remote: *** error: lines with trailing whitespace found
...
remote: *** error: sysdeps/unix/sysv/linux/statx_cp.c: trailing lines
We stopped adding "Contributed by" or similar lines in sources in 2012
in favour of git logs and keeping the Contributors section of the
glibc manual up to date. Removing these lines makes the license
header a bit more consistent across files and also removes the
possibility of error in attribution when license blocks or files are
copied across since the contributed-by lines don't actually reflect
reality in those cases.
Move all "Contributed by" and similar lines (Written by, Test by,
etc.) into a new file CONTRIBUTED-BY to retain record of these
contributions. These contributors are also mentioned in
manual/contrib.texi, so we just maintain this additional record as a
courtesy to the earlier developers.
The following scripts were used to filter a list of files to edit in
place and to clean up the CONTRIBUTED-BY file respectively. These
were not added to the glibc sources because they're not expected to be
of any use in future given that this is a one time task:
https://gist.github.com/siddhesh/b5ecac94eabfd72ed2916d6d8157e7dchttps://gist.github.com/siddhesh/15ea1f5e435ace9774f485030695ee02
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
I used these shell commands:
../glibc/scripts/update-copyrights $PWD/../gnulib/build-aux/update-copyright
(cd ../glibc && git commit -am"[this commit message]")
and then ignored the output, which consisted lines saying "FOO: warning:
copyright statement not found" for each of 6694 files FOO.
I then removed trailing white space from benchtests/bench-pthread-locks.c
and iconvdata/tst-iconv-big5-hkscs-to-2ucs4.c, to work around this
diagnostic from Savannah:
remote: *** pre-commit check failed ...
remote: *** error: lines with trailing whitespace found
remote: error: hook declined to update refs/heads/master
and add _nocancel variant.
* sysdeps/mach/hurd/Makefile [io] (sysdep_routines): Add fcntl_nocancel.
* sysdeps/mach/hurd/fcntl.c [NOCANCEL]: Include <not-cancel.h>.
[!NOCANCEL]: Include <sysdep-cancel.h>.
(__libc_fcntl) [!NOCANCEL]: Surround __file_record_lock call with enabling async cancel, and use HURD_FD_PORT_USE_CANCEL instead of HURD_FD_PORT_USE.
* sysdeps/mach/hurd/fcntl_nocancel.c: New file, defines __fcntl_nocancel by including fcntl.c.
* sysdeps/mach/hurd/not-cancel.h (__fcntl64_nocancel): Replace macro with
__fcntl_nocancel declaration with hidden proto, and make
__fcntl64_nocancel call __fcntl_nocancel.
and add _nocancel variant.
* sysdeps/mach/hurd/Makefile [io] (sysdep_routines): Add wait4_nocancel.
* sysdeps/mach/hurd/wait4.c: Include <sysdep-cancel.h>
(__wait4): Surround __proc_wait with enabling async cancel, and use
__USEPORT_CANCEL instead of __USEPORT.
* sysdeps/mach/hurd/wait4_nocancel.c: New file, contains previous
implementation of __wait4.
* sysdeps/mach/hurd/not-cancel.h (__waitpid_nocancel): Replace macro with
__wait4_nocancel declaration with hidden proto, and make
__waitpid_nocancel call __wait4_nocancel.
* sysdeps/mach/hurd/Makefile [subdir=misc] (sysdep_routines): Add
writev_nocancel writev_nocancel_nostatus.
* sysdeps/mach/hurd/not-cancel.h (__writev_nocancel_nostatus): Replace
macro with function declaration (with hidden prototype in libc).
(__writev_nocancel): New function declaration (with hidden prototype in libc).
* sysdeps/mach/hurd/writev_nocancel_nostatus.c: New file.
* sysdeps/posix/writev_nocancel.c: New file, includes writev.c to make a
nocancel variant that calls __write_nocancel.
* sysdeps/posix/writev.c (writev): Do not define alias if __writev is
renamed.
and add _nocancel variants.
* sysdeps/mach/hurd/write.c (__libc_write): Call __write_nocancel
surrounded by enabling async cancel, to replace implementation moved
to...
* sysdeps/mach/hurd/write_nocancel.c (__write_nocancel): ... here.
* sysdeps/mach/hurd/pwrite64.c (__libc_pwrite64): Call
__pwrite64_nocancel surrounded by enabling async cancel, to replace
implementation moved to...
* sysdeps/mach/hurd/pwrite64_nocancel.c (__pwrite64_nocancel): ... here.
* sysdeps/mach/hurd/Makefile (sysdep_routines): Add write_nocancel and
pwrite64_nocancel.
* sysdeps/mach/hurd/not-cancel.h (__write_nocancel,
__pwrite64_nocancel): Replace macros with prototypes with a hidden proto on
libc.
* sysdeps/mach/hurd/dl-sysdep.c (__write_nocancel): New alias, check
that it is not hidden.
* sysdeps/mach/hurd/Versions (libc.GLIBC_PRIVATE): Add __write_nocancel.
(ld.GLIBC_PRIVATE): Add __write_nocancel.
* sysdeps/mach/hurd/i386/localplt.data (__write_nocancel): Add
reference.
and add _nocancel variants.
* sysdeps/mach/hurd/pread64.c (__libc_pread64): Call __pread64_nocancel
surrounded by enabling async cancel, to replace implementation moved to...
* sysdeps/mach/hurd/pread64_nocancel.c (__pread64_nocancel): ... here.
* sysdeps/mach/hurd/read.c (__libc_read): Call __read_nocancel surrounded by
enabling async cancel, to replace implementation moved to...
* sysdeps/mach/hurd/read_nocancel.c (__read_nocancel): ... here.
* sysdeps/mach/hurd/Makefile (sysdep_routines): Add read_nocancel and
pread64_nocancel.
* sysdeps/mach/hurd/not-cancel.h (__read_nocancel, __pread64_nocancel):
Replace macros with prototypes with a hidden proto on libc.
* sysdeps/mach/hurd/dl-sysdep.c: Include <not-cancel.h>.
(__pread64_nocancel): New alias, check that it is not hidden.
(__read_nocancel): New alias, check that it is not hidden.
* sysdeps/mach/hurd/Versions (libc.GLIBC_PRIVATE): Add __read_nocancel and
__pread64_nocancel.
(ld.GLIBC_2.1): Add __pread64.
(ld.GLIBC_PRIVATE): Add __read_nocancel and __pread64_nocancel.
* sysdeps/mach/hurd/i386/ld.abilist (__pread64): Add symbol.
* sysdeps/mach/hurd/i386/localplt.data (__read_nocancel, __pread64,
__pread64_nocancel): Add references.
Not only libc/rtld use __close_nocancel_nostatus.
* sysdeps/mach/hurd/Makefile [$(subdir) == io] (sysdep_routines): Add
close_nocancel_nostatus.
* sysdeps/mach/hurd/Versions (libc): Add __close_nocancel_nostatus to
GLIBC_PRIVATE.
* sysdeps/mach/hurd/not-cancel.h (__close_nocancel_nostatus): Declare
function instead of defining inline.
[IS_IN (libc) || IS_IN (rtld)] (__close_nocancel_nostatus): Make
function hidden.
* sysdeps/mach/hurd/close_nocancel_nostatus.c: New file.
