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Date: Mon, 13 Jun 2022 10:04:55 -0700 From: Kees Cook <keescook@...omium.org> To: Uladzislau Rezki <urezki@...il.com> Cc: Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org, Zorro Lang <zlang@...hat.com>, linux-xfs@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH 1/3] usercopy: Handle vm_map_ram() areas On Mon, Jun 13, 2022 at 07:02:10PM +0200, Uladzislau Rezki wrote: > On Mon, Jun 13, 2022 at 05:44:35PM +0100, Matthew Wilcox wrote: > > On Mon, Jun 13, 2022 at 09:23:15AM -0700, Kees Cook wrote: > > > On Sun, Jun 12, 2022 at 10:32:25PM +0100, Matthew Wilcox (Oracle) wrote: > > > > vmalloc does not allocate a vm_struct for vm_map_ram() areas. That causes > > > > us to deny usercopies from those areas. This affects XFS which uses > > > > vm_map_ram() for its directories. > > > > > > > > Fix this by calling find_vmap_area() instead of find_vm_area(). > > > > > > Thanks for the fixes! > > > > > > > [...] > > > > + /* XXX: We should also abort for free vmap_areas */ > > > > > > What's needed to detect this? > > > > I'm not entirely sure. I only just learned of the existence of this > > struct ;-) > > > > /* > > * The following two variables can be packed, because > > * a vmap_area object can be either: > > * 1) in "free" tree (root is free_vmap_area_root) > > * 2) or "busy" tree (root is vmap_area_root) > > */ > > union { > > unsigned long subtree_max_size; /* in "free" tree */ > > struct vm_struct *vm; /* in "busy" tree */ > > }; > > > > Hmm. Actually, we only search vmap_area_root, so I suppose it can't > > be a free area. So this XXX can be removed, as we'll get NULL back > > if we've got a pointer to a free area. Ulad, do I have this right? > > > Yep, we find here only allocated areas which bind to the "vmap_area_root" > tree, so it can not be a freed area. So we will not get a pointer to the > free area :) Thanks! I've tweaked the patch to drop the XXX comment. -- Kees Cook
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