linux-kernel - Re: [PATCH] sg, bsg: mitigate read/write abuse, block uaccess in release

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <20180615164930.GE30522@ZenIV.linux.org.uk>
Date:   Fri, 15 Jun 2018 17:49:30 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Jann Horn <jannh@...gle.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
        Doug Gilbert <dgilbert@...erlog.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        security@...nel.org
Subject: Re: [PATCH] sg, bsg: mitigate read/write abuse, block uaccess in
 release

On Fri, Jun 15, 2018 at 05:23:35PM +0200, Jann Horn wrote:
> As Al Viro noted in commit 128394eff343 ("sg_write()/bsg_write() is not fit
> to be called under KERNEL_DS"), sg and bsg improperly access userspace
> memory outside the provided buffer, permitting kernel memory corruption via
> splice().
> But they don't just do it on ->write(), also on ->read() and (in the case
> of bsg) even on ->release().
> 
> As a band-aid, make sure that the ->read() and ->write() handlers can not
> be called in weird contexts (kernel context or credentials different from
> file opener), like for ib_safe_file_access().
> Also, completely prevent user memory accesses from ->release().

Band-aid it is, and a bloody awful one, at that.  What the hell is going on
in bsg_put_device() and can it _ever_ hit that call chain?  I.e.
	bsg_release()
		bsg_put_device()
			blk_complete_sgv4_hdr_rq()
				->complete_rq()
					copy_to_user()
If it can, the whole thing is FUBAR by design - ->release() may bloody well
be called in a context that has no userspace at all.

This is completely insane; what's going on there?