linux-kernel - RE: [GIT PULL] percpu fix for v5.9-rc6

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <776bcc3e3814433a8ed2c2027a2cf7c1@AcuMS.aculab.com>
Date:   Sat, 19 Sep 2020 15:15:08 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Arvind Sankar' <nivedita@...m.mit.edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Matthew Wilcox <willy@...radead.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>
Subject: RE: [GIT PULL] percpu fix for v5.9-rc6

From: Arvind Sankar
> Sent: 18 September 2020 23:40
..
> Ouch, offsetof() and sizeof() will give different results in the
> presence of alignment padding.
> 
> https://godbolt.org/z/rqnxTK
> 
> I think, grepping at random, that at least struct scsi_vpd is like this,
> size is 24 but data[] starts at offset 20.
> 
> 	struct scsi_vpd {
> 		struct rcu_head	rcu;
> 		int		len;
> 		unsigned char	data[];
> 	};

For another standards 'brain-fart' consider:
	x = malloc(offsetof(struct scsi_vpd, data[count]));

Since offsetof() is defined to return a compile-time constant
(hi Microsoft) this is illegal unless 'count' is also a
compile-time constant.
(It ought to be defined to be constant if the field is constant.)

If count < 4 then *x = *y will also write past the end of x.
Such structure assignments should be compile-time errors.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)