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Message-ID: <20171030073956.GA17153@kroah.com> Date: Mon, 30 Oct 2017 08:39:56 +0100 From: Greg KH <gregkh@...uxfoundation.org> To: Theodore Ts'o <tytso@....edu>, Chen Feng <puck.chen@...ilicon.com>, zhaoyukun@...wei.com, arnd@...db.de, linux-kernel@...r.kernel.org, suzhuangluan@...ilicon.com, dan.zhao@...ilicon.com Subject: Re: [PATCH RFC] random: fix syzkaller fuzzer test int overflow On Sun, Oct 29, 2017 at 02:25:29PM -0400, Theodore Ts'o wrote: > On Sat, Oct 28, 2017 at 11:22:00AM +0800, Chen Feng wrote: > > > > I checked the ioctl. What's the purpose of RNDADDTOENTCNT ioctl to > > userspace? > > It's a legacy ioctl which is probably not used anywhere; it's been > replaced by RNDADDENTROPY. It previously allows root to bump the > entropy estimate, but the right way to do this by rngd is to > atomically add entropy to the pool land and bump the entropy estimate > at the same time. > > The UBSAN is harmless. The ioctl requires root, and the entropy_total > field, which is involved in the UBSAN, is only used in the first few > seconds of boot, to determine when the entropy pool has been > initialized. In general on desktop and servers this happens before > userspace has a chance to run. > > In any case, here's a fix for this. > > - Ted > > commit 6f7034d0c52e21f30002b95126b6b98e4618dc57 > Author: Theodore Ts'o <tytso@....edu> > Date: Sun Oct 29 14:17:26 2017 -0400 > > random: use a tighter cap in credit_entropy_bits_safe() > > This fixes a harmless UBSAN where root could potentially end up > causing an overflow while bumping the entropy_total field (which is > ignored once the entropy pool has been initialized, and this generally > is completed during the boot sequence). > > This is marginal for the stable kernel series, but it's a really > trivial patch, and it UBSAN warning that might cause security folks to > get overly excited for no reason. > > Signed-off-by: Theodore Ts'o <tytso@....edu> > Cc: stable@...r.kernel.org No "Reported-by:"? thanks, greg k-h
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