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?
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