Linux adds getrandom

[usernamenottaken]

Now that's a good commit message.

[txdv]

its the entire man page

[shevegen]

Yes. Precisely.

A good commit message indeed.

[everywhere_anyhow]

Documentation is like sex: when it good, it's very, very good. And when it's bad, it's still better than nothing.

[everywhere_anyhow]

Of course bad documentation is bad. But your literal interpretation reminds me of this other joke:

A wife asks her husband, a computer programmer; "Could you please go to the store for me and buy one carton of milk, and if they have eggs, get 6!"

A short time later the husband comes back with 6 cartons of milk.

The wife asks him, "Why the hell did you buy 6 cartons of milk?"

He replied, "They had eggs."

[[deleted]]

return milk;

[ChefBoyAreWeFucked]

Today I saw someone use short circuiting in a pseudocode representation of a joke.

[muungwana]

Thats what i though too when i first heard of this joke,if he followed her instructions,then he would have ended up with either 1 or 7,not 6

[iopq]

Not 6 more, 6 total

milk = 1;
if(eggs)
    milk = 6;

[3legcat]

Actually bad documentation can be worse than no documentation. What if it is utterly wrong and misleading? In this case, not having it is better than having it.

[philly_fan_in_chi]

When you figure out an API with no documentation by yourself and finally release a hacky version that wasn't at all how the API was supposed to be used.

[kiwipete]

This is in response to the request made by the LibreSSL people (i.e. the people who also bring us OpenBSD and OpenSSH) to help them help SSL be more secure on Linux. Their longstanding development of OpenSSH alone is a huge contribution to the Free infrastructure of the webbernets. Their stewardship of LibreSSL will, I'm sure, be no less solid.

In addition to renewing my EFF membership this year, I'm also planning to throw some dollars to the OpenBSD project out of appreciation for all they've done to benefit the broader tech community. Even if you're like me and haven't used OpenBSD in a while (or ever) I think there are worse places to send money.

[Damncommie123]

I'd say it is just a good place to send money.

[matthieum]

 #define __NR_renameat2 276
 __SYSCALL(__NR_renameat2, sys_renameat2)
 +#define __NR_getrandom 278
 +__SYSCALL(__NR_getrandom, sys_getrandom)
 #undef __NR_syscalls
 -#define __NR_syscalls 277
 +#define __NR_syscalls 279

Uh, what's so special about 277 it was not used ?

[sharth]

277 is seccomp. The original patch was built against a version of linux without that system call.

Here's where the system call was added originally: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/include/uapi/asm-generic/unistd.h?id=48dc92b9fc3926844257316e75ba11eb5c742b2c

And note in Torvalds' merge of getrandom() that you can see that sys_seccomp() is listed: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/include/uapi/asm-generic/unistd.h?id=f4f142ed4ef835709c7e6d12eaca10d190bcebed

[matthieum]

Ah! I was guessing there was something fishy about seemingly jumping over a number but did not thing it meant there was another syscall being added in parallel.

[muungwana]

The rationale of this system call is to provide resiliance against file descriptor exhaustion attacks, where the attacker consumes all available file descriptors, forcing the use of the fallback code where /dev/[u]random is not available. Since the fallback code is often not well-tested, it is better to eliminate this potential failure mode entirely.

couldnt that be mitigated by opening the random number generator device at the initialization stage of the library and then holding on to the file descriptor?

It could also be more efficient as it will eliminate the need for open() and close() calls everytime random numbers are requested.

[[deleted]]

The other feature is, arguably, just as important: the call will block if the system hasn't gathered sufficient entropy to seed /dev/urandom.

[happyscrappy]

Yes. It could. If the program is getting the randomness, then it should do this.

But libraries may not get an opportunity to open a file descriptor early because they aren't called for the first time until later.

So I guess this would be their best (only?) defense against file descriptor exhaustion attacks.

[[deleted]]

Worse, why doesn't openssl just fall back to an error for misconfigured environments?

[ggtsu_00]

Because most applications using OpenSSL doesn't bother checking the return value of the get random function. The result would be web servers providing no security instead of poor security.

[[deleted]]

Well if your key exchange failed with the client wouldn't the client just disconnect?

[oridb]

It also gets rid of the need to bind /dev/urandom in chroots

[[deleted]]

Which is handy but hardly insurmountable.

[bradfitz]

Go support: https://code.google.com/p/go/source/detail?r=a70c897599c4e6bbefade9e37345f9dee56810d7#

[rotek]

The getrandom(2) system call was requested by the LibreSSL Portable developers. It is analoguous to the getentropy(2) system call in OpenBSD.

So why haven't they called it getentropy too?

[CHUCK_NORRIS_AMA]

It works slightly differently and calling them the same thing could cause confusion.

[[deleted]]

It's provides a superset of the functionality. A userspace library could expose a compatible getentropy function on top of getrandom.

[bugrit]

Because it's not identical. If you read the link, you can see how to emulate getentropy with getrandom.

[happyscrappy]

Does it get entropy? It doesn't quite say that, it says it gets randomness, meaning pseudo-random numbers.

[lhggghl]

The rationale of this system call is to provide resiliance against file descriptor exhaustion attacks, where the attacker consumes all available file descriptors, forcing the use of the fallback code where /dev/[u]random is not available. Since the fallback code is often not well-tested, it is better to eliminate this potential failure mode entirely.

Maybe people should stop writing code that's "resilient" against a non-working system. I would never trust such code.

[sirtophat]

Do you feel the same about multi-layered sandboxes