Date: Fri, 9 Jul 2021 18:41:36 -0400 From: Shawn Webb <shawn.webb@hardenedbsd.org> To: Warner Losh <imp@bsdimp.com> Cc: Warner Losh <imp@freebsd.org>, src-committers <src-committers@freebsd.org>, "<dev-commits-src-all@freebsd.org>" <dev-commits-src-all@freebsd.org>, dev-commits-src-main@freebsd.org Subject: Re: git: 72821668b039 - main - stand/kmem_zalloc: panic when a M_WAITOK allocation fails Message-ID: <20210709224136.qprhblk43ndtmxqf@mutt-hbsd> In-Reply-To: <CANCZdfr4X%2Bjg5c1WrUWDMVDy9MmZMB%2Bp_%2BW09AKhNt7%2Bu1Fhxg@mail.gmail.com> References: <202107091726.169HQvGQ084473@gitrepo.freebsd.org> <20210709195425.xzk2azaor4ielmb4@mutt-hbsd> <CANCZdfr4X%2Bjg5c1WrUWDMVDy9MmZMB%2Bp_%2BW09AKhNt7%2Bu1Fhxg@mail.gmail.com>
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--53mirfa322pvcatr Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Jul 09, 2021 at 02:34:12PM -0600, Warner Losh wrote: > On Fri, Jul 9, 2021 at 1:54 PM Shawn Webb <shawn.webb@hardenedbsd.org> > wrote: >=20 > > On Fri, Jul 09, 2021 at 05:26:57PM +0000, Warner Losh wrote: > > > The branch main has been updated by imp: > > > > > > URL: > > https://cgit.FreeBSD.org/src/commit/?id=3D72821668b039c276914569e9caa1c= dfa4e4cb674 > > > > > > commit 72821668b039c276914569e9caa1cdfa4e4cb674 > > > Author: Warner Losh <imp@FreeBSD.org> > > > AuthorDate: 2021-07-09 17:21:18 +0000 > > > Commit: Warner Losh <imp@FreeBSD.org> > > > CommitDate: 2021-07-09 17:21:18 +0000 > > > > > > stand/kmem_zalloc: panic when a M_WAITOK allocation fails > > > > > > Malloc() might return NULL, in which case we will panic with a NU= LL > > > pointer deref. Make it panic when the allocation fails to preserve > > the > > > postcondtion that we never return a non-NULL value. > > > > malloc(9) tells us that M_WAITOK will never fail. I'm thinking this > > conditional might need to be negated for the !M_WAITOK case, in which > > malloc(9) could indeed fail. > > > > Although, even as I type this email, I just realized that a different > > function, Malloc, is being called. What's the difference between > > malloc and Malloc? > > >=20 > The block of code is to be used in the standalone environment. > The Malloc() function there doesn't have wait/nowait variants and > can fail (though in the boot loader, that almost never happens except > when there's a bug). The code is for wrappers around kmem_zalloc > which is the OpenZFS spelling of malloc. It assumes that kmem_zalloc > with M_WAITOK will never return NULL, so it never checks. This > changes a weird panic when the returned NULL pointer is dereferenced, > to an orderly panic when the malloc that the code assumes will never > fail actuall fails. This at least gives better context of where the error > happened and what the error was. In practice, this is a big nop, but > we have had issues with other Malloc calls in the past failing because > of bugs that caused us to ask for a ridiculous amount of memory. >=20 > Make sense? That makes much more sense. Thanks a lot for the clarification! --=20 Shawn Webb Cofounder / Security Engineer HardenedBSD https://git.hardenedbsd.org/hardenedbsd/pubkeys/-/raw/master/Shawn_Webb/03A= 4CBEBB82EA5A67D9F3853FF2E67A277F8E1FA.pub.asc --53mirfa322pvcatr Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEA6TL67gupaZ9nzhT/y5nonf44foFAmDo0J4ACgkQ/y5nonf4 4fq4tRAAoQKdCupdv+PZ+1R36+kh9uRyFkOk+/fR5VkQl8anqid7GMAYx6fwEC5k bsqj95tIBJZ00iV0pjoqdCJYgzmBAOcrs8ZNNka1Q42kgSyqk+xgHe2MHGnVaQ7g 60zCj8267dpo+nhQVp0vkffpSgb+qpLm9wKZQ0wDe4hExyZNBabSfOubCrLDCkwW m8t/iG0laOAtbRNJ2EqWuELIAkqKZpuume0KUH4iL14d8RjhpPCQecwA7orPZnDU sZnO2te2qQbckBRhfCNEMNW7pBY7JfIPyzqfa4Bk0vdWtm7PIJnFwxi59IvqWKtZ jwCWMNzNNIt9wZDOnB0ktuLZWRxQvCqcV2SQ96lDIQCbWYEnzxItGqD9INpqh3y2 Jfl7dnWDmcnnHHfHYRaYJgW4yEqnqpAB8V/BhgES4bnYN4vCst3LWheEPBpKOe3s Ar4735O+QwdR9hFKyHPVeVokaeFSu46mfD/3/li1F7/HcLNKpqs7KxvCksZE+uHq Fv3n7ddWrndI+DTkFzPtvleVBQjhpS828rgoP5jCC6liFRkOp/omFD85g4l68L73 ejKAn6ZWiP/LzS/8La9xDfHRQ3SMsw8CVO81m83b9WixDlnCLLx66WGnA596pMkb OFvNA7c4hZHr9z5H46/C2hZ8G9mpaW2e7R/U2IbkN8y4x0bSTj8= =RxBr -----END PGP SIGNATURE----- --53mirfa322pvcatr--
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