Messages in this thread | | | From | Eric Dumazet <> | Date | Thu, 25 May 2017 10:15:11 -0700 | Subject | Re: [PATCH] [iov_iter] use memmove() when copying to/from user page |
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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.
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