From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Mark Harris <mark.hsj@gmail.com>
Cc: libc-alpha@sourceware.org, Florian Weimer <fweimer@redhat.com>,
linux-crypto@vger.kernel.org
Subject: Re: [PATCH v2] arc4random: simplify design for better safety
Date: Tue, 26 Jul 2022 12:41:13 +0200 [thread overview]
Message-ID: <Yt/EySjdJjYW/EcB@zx2c4.com> (raw)
In-Reply-To: <CAMdZqKH=9mDhoW_gpL-pUEQAGuN=orc1doudyAuHdoPc7O53RQ@mail.gmail.com>
Hi Mark,
On Mon, Jul 25, 2022 at 06:10:06PM -0700, Mark Harris wrote:
> Jason A. Donenfeld wrote:
> > + l = __getrandom_nocancel (p, n, 0);
> > + if (l > 0)
> > + {
> > + if ((size_t) l == n)
> > + return; /* Done reading, success. */
> > + p = (uint8_t *) p + l;
> > + n -= l;
> > + continue; /* Interrupted by a signal; keep going. */
> > + }
> > + else if (l == 0)
> > + arc4random_getrandom_failure (); /* Weird, should never happen. */
> > + else if (errno == ENOSYS)
> > + {
> > + have_getrandom = false;
> > + break; /* No syscall, so fallback to /dev/urandom. */
> > + }
> > + arc4random_getrandom_failure (); /* Unknown error, should never happen. */
>
> Isn't EINTR also possible? Aborting in that case does not seem reasonable.
Not in current kernels, where it always returns at least PAGE_SIZE bytes
before checking for pending signals. In older kernels, if there was a
signal pending at the top, it would do no work and return -ERESTARTSYS,
which I believe should then get restarted by glibc's syscaller? I might
be wrong about how restarts work though, so if you know better, please
let me know. TEMP_FAILURE_RETRY relies on errno, so that's not what we
want. I guess I can just add a case for it.
> Also the __getrandom_nocancel function does not set errno on Linux; it
> just returns INTERNAL_SYSCALL_CALL (getrandom, buf, buflen, flags).
> So unless that is changed, it doesn't look like this ENOSYS check will
> detect old Linux kernels.
Thanks. It looks like INTERNAL_SYSCALL_CALL just returns the errno as-is
as a return value, right? I'll adjust the code to account for that.
> > + struct pollfd pfd = { .events = POLLIN };
> > + pfd.fd = TEMP_FAILURE_RETRY (
> > + __open64_nocancel ("/dev/random", O_RDONLY | O_CLOEXEC | O_NOCTTY));
> > + if (pfd.fd < 0)
> > + arc4random_getrandom_failure ();
> > + if (__poll (&pfd, 1, -1) < 0)
> > + arc4random_getrandom_failure ();
> > + if (__close_nocancel (pfd.fd) < 0)
> > + arc4random_getrandom_failure ();
>
> The TEMP_FAILURE_RETRY handles EINTR on open, but __poll can also
> result in EINTR.
Thanks. I'll surround the __poll in TEMP_FAILURE_RETRY.
Thank you for the review! v3 will have the above changes.
Jason
next prev parent reply other threads:[~2022-07-26 10:41 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <YtwgTySJyky0OcgG@zx2c4.com>
2022-07-23 16:25 ` arc4random - are you sure we want these? Jason A. Donenfeld
2022-07-23 17:18 ` Paul Eggert
2022-07-24 23:55 ` Jason A. Donenfeld
2022-07-25 20:31 ` Paul Eggert
2022-07-23 17:39 ` Adhemerval Zanella Netto
2022-07-23 22:54 ` Jason A. Donenfeld
2022-07-25 15:33 ` Rich Felker
2022-07-25 15:59 ` Adhemerval Zanella Netto
2022-07-25 17:41 ` Rich Felker
2022-07-25 16:18 ` Sandy Harris
2022-07-25 16:40 ` Florian Weimer
2022-07-25 16:49 ` Adhemerval Zanella Netto
2022-07-25 16:51 ` Jason A. Donenfeld
2022-07-25 17:44 ` Rich Felker
2022-07-25 18:33 ` Cristian Rodríguez
2022-07-25 18:49 ` Rich Felker
2022-07-27 1:54 ` Theodore Ts'o
2022-07-27 2:16 ` Rich Felker
2022-07-27 2:45 ` Theodore Ts'o
2022-07-27 11:34 ` Adhemerval Zanella Netto
2022-07-27 12:32 ` Theodore Ts'o
2022-07-27 12:49 ` Florian Weimer
2022-07-27 20:15 ` Theodore Ts'o
2022-07-27 21:59 ` Rich Felker
2022-07-28 0:30 ` Theodore Ts'o
2022-07-28 0:39 ` Cristian Rodríguez
2022-07-27 15:39 ` Rich Felker
2022-07-23 19:04 ` Cristian Rodríguez
2022-07-23 22:59 ` Jason A. Donenfeld
2022-07-24 16:23 ` Cristian Rodríguez
2022-07-24 21:57 ` Jason A. Donenfeld
2022-07-25 10:14 ` Florian Weimer
2022-07-25 10:11 ` Florian Weimer
2022-07-25 11:04 ` Jason A. Donenfeld
2022-07-25 12:39 ` Florian Weimer
2022-07-25 13:43 ` Jason A. Donenfeld
2022-07-25 13:58 ` Cristian Rodríguez
2022-07-25 16:06 ` Rich Felker
2022-07-25 16:43 ` Florian Weimer
2022-07-26 14:27 ` Overwrittting AT_RANDOM after use (was Re: arc4random - are you sure we want these?) Yann Droneaud
2022-07-26 14:35 ` arc4random - are you sure we want these? Yann Droneaud
2022-07-25 13:25 ` Jeffrey Walton
2022-07-25 13:48 ` Jason A. Donenfeld
2022-07-25 14:56 ` Rich Felker
2022-07-25 22:57 ` [PATCH] arc4random: simplify design for better safety Jason A. Donenfeld
2022-07-25 23:11 ` Jason A. Donenfeld
2022-07-25 23:28 ` [PATCH v2] " Jason A. Donenfeld
2022-07-25 23:59 ` Eric Biggers
2022-07-26 10:26 ` Jason A. Donenfeld
2022-07-26 1:10 ` Mark Harris
2022-07-26 10:41 ` Jason A. Donenfeld [this message]
2022-07-26 11:06 ` Florian Weimer
2022-07-26 16:51 ` Mark Harris
2022-07-26 18:42 ` Jason A. Donenfeld
2022-07-26 19:18 ` Adhemerval Zanella Netto
2022-07-26 19:24 ` Jason A. Donenfeld
2022-07-26 9:55 ` Florian Weimer
2022-07-26 11:04 ` Jason A. Donenfeld
2022-07-26 11:07 ` [PATCH v3] " Jason A. Donenfeld
2022-07-26 11:11 ` Jason A. Donenfeld
2022-07-26 11:12 ` [PATCH v2] " Florian Weimer
2022-07-26 11:20 ` Jason A. Donenfeld
2022-07-26 11:35 ` Adhemerval Zanella Netto
2022-07-26 11:33 ` Adhemerval Zanella Netto
2022-07-26 11:54 ` Jason A. Donenfeld
2022-07-26 12:08 ` Jason A. Donenfeld
2022-07-26 12:20 ` Jason A. Donenfeld
2022-07-26 12:34 ` Adhemerval Zanella Netto
2022-07-26 12:47 ` Jason A. Donenfeld
2022-07-26 13:11 ` Adhemerval Zanella Netto
2022-07-26 13:30 ` [PATCH v4] " Jason A. Donenfeld
2022-07-26 15:21 ` Yann Droneaud
2022-07-26 16:20 ` Adhemerval Zanella Netto
2022-07-26 18:36 ` Jason A. Donenfeld
2022-07-26 19:08 ` [PATCH v5] " Jason A. Donenfeld
2022-07-26 19:58 ` [PATCH v6] " Jason A. Donenfeld
2022-07-26 20:17 ` Adhemerval Zanella Netto
2022-07-26 20:56 ` Adhemerval Zanella Netto
2022-07-28 10:29 ` Szabolcs Nagy
2022-07-28 10:36 ` Szabolcs Nagy
2022-07-28 11:01 ` Adhemerval Zanella
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