ACK: [SRU bionic] random: Make getrandom() ready earlier

[Khaled Elmously]

On 2018-07-04 11:12:36 , Khaled Elmously wrote:
> On 2018-07-04 15:56:35 , Colin Ian King wrote:
> > On 04/07/18 15:15, Stefan Bader wrote:
> > > From: Ben Hutchings <ben at decadent.org.uk>
> > > 
> > > This effectively reverts commit 725e828 "random: fix crng_ready()
> > > test" which was commit 43838a23a05f upstream.  Unfortunately some
> > > users of getrandom() don't expect it to block for long, and they need
> > > to be fixed before we can allow this change into stable.
> > > 
> > > This doesn't directly revert that commit, but only weakens the ready
> > > condition used by getrandom() when the GRND_RANDOM flag is not set.
> > > Calls to getrandom() that return before the RNG is fully seeded will
> > > generate warnings, just like reads from /dev/urandom.
> > > 
> > > https://bugs.launchpad.net/bugs/1780062
> > > 
> > > (backported from ://salsa.debian.org/kernel-team/linux/raw/stretch/debian/patches/debian/random-make-getrandom-ready-earlier.patch)
> > > [smb: open code waiting in getrandom directly]
> > > Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
> > > ---
> > > This is based on the patch from Ben Hutchings in Debian. But since
> > > wait_for_random_bytes, which is used in the 4.15 code is exported
> > > and used by other things, I did instead do its own wait in getrandom().
> > > 
> > > -Stefan
> > > 
> > >  drivers/char/random.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/char/random.c b/drivers/char/random.c
> > > index d5f1211..6021405 100644
> > > --- a/drivers/char/random.c
> > > +++ b/drivers/char/random.c
> > > @@ -1976,10 +1976,10 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
> > >  	if (flags & GRND_RANDOM)
> > >  		return _random_read(flags & GRND_NONBLOCK, buf, count);
> > >  
> > > -	if (!crng_ready()) {
> > > +	if (crng_init == 0) {
> > >  		if (flags & GRND_NONBLOCK)
> > >  			return -EAGAIN;
> > > -		ret = wait_for_random_bytes();
> > > +		ret = wait_event_interruptible(crng_init_wait, crng_init > 0);
> > >  		if (unlikely(ret))
> > >  			return ret;
> > >  	}
> > > 
> > 
> > Looks good to me; this is a good workaround for now; fixes the issue on
> > my X230 too, so I've tested this and it works.
> > 
> > The bug link needs fixing up when this is applied.
> 
> The buglink seems to work fine for me (just don't copy the closing
> parenthesis)
>

Sorry, I misspoke. I meant the "patch link" works fine for me (though
the bug link seems to work fine too)


> > 
> > Thanks Stefan.
> > 
> > Acked-by: Colin Ian King <colin.king at canonical.com>
> > 
> > -- 
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> > kernel-team at lists.ubuntu.com
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