Messages in this thread | | | Date | Thu, 25 May 2017 23:27:15 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH] [iov_iter] use memmove() when copying to/from user page |
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On Thu 2017-05-25 10:15:11, Eric Dumazet wrote: > On Thu, May 25, 2017 at 10:04 AM, Pavel Machek <pavel@ucw.cz> wrote: > > Hi! > > > > On Tue 2017-05-16 23:48:54, Al Viro wrote: > >> On Tue, May 16, 2017 at 03:15:16PM -0700, Dmitry Vyukov wrote: > >> > > Because it's not going to be *one* call of memcpy() or memmove(). It's > >> > > one per page. > >> > > >> > > >> > I missed that. > >> > > >> > I assumed that in the case of sendfile from memfd to memfd data will > >> > be copied directly. But it goes through a pipe with multiple buffers. > >> > Does not look easily fixable. > >> > >> Which leaves us only with "will nasal demons really fly there?". > > > > It seems so: > > > > Date: Tue, 16 May 2017 14:27:34 +0200 > > From: Alexander Potapenko <glider@google.com> > > Subject: [PATCH] [iov_iter] use memmove() when copying to/from user > > page > > > > BUG: memcpy-param-overlap in generic_perform_write+0x551/0xa20 > > __msan_memcpy(ffff88013c6e3001, ffff88013c6e3000, 105) > > CPU: 0 PID: 1040 Comm: probe Not tainted 4.11.0-rc5+ #2562 > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs > > 01/01/2011 > > > > At the very least, we do not want userland to trigger kernel > > BUG()s... so this needs fixes beyond documentation. > > To be fair, this BUG() only happens because Alexander added one in memcpy() , > testing for the cases where memmove() should have been used. > > Kind of a debugging trap if you prefer. > > This is not something that a pristine kernel would do.
Aha, so BUG() is not realy a problem. Problem is that memcpy() may not be called on overlapping regions, and may do something stupid; but we don't have evidence that it does.
Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html [unhandled content-type:application/pgp-signature] | |