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Open Source and information security mailing list archives
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Date: Wed, 12 Oct 2022 18:37:11 -0700 From: Joe Perches <joe@...ches.com> To: David Laight <David.Laight@...LAB.COM>, "Jason A. Donenfeld" <Jason@...c4.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Cc: "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>, "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>, "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>, "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>, "linux-stm32@...md-mailman.stormreply.com" <linux-stm32@...md-mailman.stormreply.com>, "drbd-dev@...ts.linbit.com" <drbd-dev@...ts.linbit.com>, "dev@...nvswitch.org" <dev@...nvswitch.org>, "rds-devel@....oracle.com" <rds-devel@....oracle.com>, "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>, "dccp@...r.kernel.org" <dccp@...r.kernel.org>, "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>, "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>, "lvs-devel@...r.kernel.org" <lvs-devel@...r.kernel.org>, "SHA-cyfmac-dev-list@...ineon.com" <SHA-cyfmac-dev-list@...ineon.com>, "coreteam@...filter.org" <coreteam@...filter.org>, "tipc-discussion@...ts.sourceforge.net" <tipc-discussion@...ts.sourceforge.net>, "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>, "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>, "linux-actions@...ts.infradead.org" <linux-actions@...ts.infradead.org>, "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>, "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>, "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>, "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>, "linux-hams@...r.kernel.org" <linux-hams@...r.kernel.org>, "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "cake@...ts.bufferbloat.net" <cake@...ts.bufferbloat.net>, "brcm80211-dev-list.pdl@...adcom.com" <brcm80211-dev-list.pdl@...adcom.com>, "linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>, "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>, "linux-f2fs-devel@...ts.sourceforge.net" <linux-f2fs-devel@...ts.sourceforge.net>, "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>, "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>, "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org> Subject: Re: [PATCH v1 3/5] treewide: use get_random_u32() when possible On Wed, 2022-10-12 at 21:29 +0000, David Laight wrote: > From: Joe Perches > > Sent: 12 October 2022 20:17 > > > > On Wed, 2022-10-05 at 23:48 +0200, Jason A. Donenfeld wrote: > > > The prandom_u32() function has been a deprecated inline wrapper around > > > get_random_u32() for several releases now, and compiles down to the > > > exact same code. Replace the deprecated wrapper with a direct call to > > > the real function. > > [] > > > diff --git a/drivers/infiniband/hw/cxgb4/cm.c b/drivers/infiniband/hw/cxgb4/cm.c > > [] > > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep) > > > &ep->com.remote_addr; > > > int ret; > > > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type; > > > - u32 isn = (prandom_u32() & ~7UL) - 1; > > > + u32 isn = (get_random_u32() & ~7UL) - 1; > > > > trivia: > > > > There are somewhat odd size mismatches here. > > > > I had to think a tiny bit if random() returned a value from 0 to 7 > > and was promoted to a 64 bit value then truncated to 32 bit. > > > > Perhaps these would be clearer as ~7U and not ~7UL > > That makes no difference - the compiler will generate the same code. True, more or less. It's more a question for the reader. > The real question is WTF is the code doing? True. > The '& ~7u' clears the bottom 3 bits. > The '- 1' then sets the bottom 3 bits and decrements the > (random) high bits. Right. > So is the same as get_random_u32() | 7. True, it's effectively the same as the upper 29 bits are random anyway and the bottom 3 bits are always set. > But I bet the coder had something else in mind. Likely. And it was also likely copy/pasted a few times.
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