linux-kernel - Re: [PATCH 2/2] mm/frame-vec: use FOLL

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Message-ID: <0-v1-447bb60c11dd+174-frame_vec_fix_jgg@nvidia.com>
Date:   Mon, 5 Oct 2020 14:38:54 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     andrew Morton <akpm@...ux-foundation.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>, <linux-mm@...ck.org>
CC:     Hans Verkuil <hans.verkuil@...co.com>, Jan Kara <jack@...e.cz>,
        "Mauro Carvalho Chehab" <mchehab@....samsung.com>,
        Mel Gorman <mgorman@...e.de>, <stable@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        John Hubbard <jhubbard@...dia.com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        <linux-media@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM

When get_vaddr_frames() does its hacky follow_pfn() loop it should never
be allowed to extract a struct page from a normal VMA. This could allow a
serious use-after-free problem on any kernel memory.

Restrict this to only work on VMA's with one of VM_IO | VM_PFNMAP
set. This limits the use-after-free problem to only IO memory, which while
still serious, is an improvement.

Cc: stable@...r.kernel.org
Fixes: 8025e5ddf9c1 ("[media] mm: Provide new get_vaddr_frames() helper")
Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
---
 mm/frame_vector.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index 10f82d5643b6de..26cb20544b6c37 100644
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -99,6 +99,10 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
 		if (ret >= nr_frames || start < vma->vm_end)
 			break;
 		vma = find_vma_intersection(mm, start, start + 1);
+		if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
+			ret = -EINVAL;
+			goto out;
+		}
 	} while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
 out:
 	if (locked)
-- 
2.28.0