Date: Mon, 10 Jun 2019 16:54:09 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Doug Moore <dougm@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r348843 - head/sys/vm Message-ID: <20190610160930.S2504@besplex.bde.org> In-Reply-To: <201906100307.x5A37BFt099669@repo.freebsd.org> References: <201906100307.x5A37BFt099669@repo.freebsd.org>
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On Mon, 10 Jun 2019, Doug Moore wrote: > Log: > There are times when a len==0 parameter to mmap is okay. But on a > 32-bit machine, a len parameter just a few bytes short of 4G, rounded > up to a page boundary and hitting zero then, is not okay. Return > failure in that case. Some overflows still occur. The problem is not limited to 32-bit machines. The first overflow is for len parameter just a few bytes short of SIZE_MAX added to a page offset of a few bytes. This overflows to a small value. Then rounding up to a page boundary doesn't overflow, but gives 0 or PAGE_SIZE, so the new overflow check doesn't work and overflow still occurs. The second overflow is for a len parameter just a few bytes short of SIZE_MAX with the first overflow not occurring (usually because the offset is 0). This is now detected. > Reported by: pho > Reviewed by: alc, kib (mentor) > Tested by: pho > Differential Revision: https://reviews.freebsd.org/D20580 > > Modified: > head/sys/vm/vm_mmap.c > > Modified: head/sys/vm/vm_mmap.c > ============================================================================== > --- head/sys/vm/vm_mmap.c Sun Jun 9 22:55:21 2019 (r348842) > +++ head/sys/vm/vm_mmap.c Mon Jun 10 03:07:10 2019 (r348843) > @@ -257,7 +257,10 @@ kern_mmap(struct thread *td, uintptr_t addr0, size_t s > > /* Adjust size for rounding (on both ends). */ > size += pageoff; /* low end... */ The first overflow occurs here. Except in special cases, pageoff can be anything between 0 and PAGE_SIZE - 1, and size can be anything between 0 and SIZE_MAX. > - size = (vm_size_t) round_page(size); /* hi end */ > + /* Check for rounding up to zero. */ > + if (round_page(size) < size) > + return (EINVAL); > + size = round_page(size); /* hi end */ > > /* Ensure alignment is at least a page and fits in a pointer. */ > align = flags & MAP_ALIGNMENT_MASK; This bug was implemented in r239247 and affects all versions of FreeBSD newer than FreeBSD-7. Before then, FreeBSD used the bogus 4.4BSD check that (ssize_t)uap->len >= 0 (else return EINVAL). This behaviour was even documented. POSIX doesn't allow this -- it requires ENOMEM for invalid ranges, though it should require EOVERFLOW for ranges that are so invalid that they overflow something. Brucehelp
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