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From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, jannh@google.com,
	kirill.shutemov@linux.intel.com, linux-mm@kvack.org,
	mm-commits@vger.kernel.org, oleg@redhat.com,
	stable@vger.kernel.org, torvalds@linux-foundation.org,
	vbabka@suse.cz, willy@infradead.org, yang.shi@linux.alibaba.com
Subject: [patch 02/15] mm/mmap.c: close race between munmap() and expand_upwards()/downwards()
Date: Thu, 23 Jul 2020 21:15:11 -0700
Message-ID: <20200724041511.gcyDW6Qmq%akpm@linux-foundation.org> (raw)
In-Reply-To: <20200723211432.b31831a0df3bc2cbdae31b40@linux-foundation.org>

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: mm/mmap.c: close race between munmap() and expand_upwards()/downwards()

VMA with VM_GROWSDOWN or VM_GROWSUP flag set can change their size under
mmap_read_lock().  It can lead to race with __do_munmap():

	Thread A			Thread B
__do_munmap()
  detach_vmas_to_be_unmapped()
  mmap_write_downgrade()
				expand_downwards()
				  vma->vm_start = address;
				  // The VMA now overlaps with
				  // VMAs detached by the Thread A
				// page fault populates expanded part
				// of the VMA
  unmap_region()
    // Zaps pagetables partly
    // populated by Thread B

Similar race exists for expand_upwards().

The fix is to avoid downgrading mmap_lock in __do_munmap() if detached
VMAs are next to VM_GROWSDOWN or VM_GROWSUP VMA.

[akpm@linux-foundation.org: s/mmap_sem/mmap_lock/ in comment]
Link: http://lkml.kernel.org/r/20200709105309.42495-1-kirill.shutemov@linux.intel.com
Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Jann Horn <jannh@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>	[4.20+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mmap.c |   16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

--- a/mm/mmap.c~mm-close-race-between-munmap-and-expand_upwards-downwards
+++ a/mm/mmap.c
@@ -2620,7 +2620,7 @@ static void unmap_region(struct mm_struc
  * Create a list of vma's touched by the unmap, removing them from the mm's
  * vma list as we go..
  */
-static void
+static bool
 detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
 	struct vm_area_struct *prev, unsigned long end)
 {
@@ -2645,6 +2645,17 @@ detach_vmas_to_be_unmapped(struct mm_str
 
 	/* Kill the cache */
 	vmacache_invalidate(mm);
+
+	/*
+	 * Do not downgrade mmap_lock if we are next to VM_GROWSDOWN or
+	 * VM_GROWSUP VMA. Such VMAs can change their size under
+	 * down_read(mmap_lock) and collide with the VMA we are about to unmap.
+	 */
+	if (vma && (vma->vm_flags & VM_GROWSDOWN))
+		return false;
+	if (prev && (prev->vm_flags & VM_GROWSUP))
+		return false;
+	return true;
 }
 
 /*
@@ -2825,7 +2836,8 @@ int __do_munmap(struct mm_struct *mm, un
 	}
 
 	/* Detach vmas from rbtree */
-	detach_vmas_to_be_unmapped(mm, vma, prev, end);
+	if (!detach_vmas_to_be_unmapped(mm, vma, prev, end))
+		downgrade = false;
 
 	if (downgrade)
 		mmap_write_downgrade(mm);
_


  parent reply index

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24  4:14 incoming Andrew Morton
2020-07-24  4:15 ` [patch 01/15] mm/memory.c: avoid access flag update TLB flush for retried page fault Andrew Morton
2020-07-24  4:38   ` Yang Shi
2020-07-24  4:56     ` Andrew Morton
2020-07-24 19:27   ` Linus Torvalds
2020-07-24 20:22     ` Linus Torvalds
2020-07-25  0:36       ` Yang Shi
2020-07-25  1:29         ` Linus Torvalds
2020-07-25 15:58           ` Catalin Marinas
2020-07-28  9:22             ` Will Deacon
2020-07-28  9:39               ` Catalin Marinas
2020-07-28 10:07                 ` Yu Xu
2020-07-28 11:46                   ` Catalin Marinas
2020-07-28 10:21                 ` Will Deacon
2020-07-28 18:28                 ` Linus Torvalds
2020-07-27 17:52           ` Yang Shi
2020-07-27 18:04             ` Linus Torvalds
2020-07-27 18:42               ` Catalin Marinas
2020-07-27 20:56                 ` Linus Torvalds
2020-07-27 22:34               ` Yang Shi
2020-07-27  7:31       ` Yu Xu
2020-07-27 11:05         ` Catalin Marinas
2020-07-27 17:01           ` Linus Torvalds
2020-07-28 11:19             ` Catalin Marinas
2020-07-27 17:12           ` Yu Xu
2020-07-27 18:04             ` Yang Shi
2020-07-27 18:37               ` Linus Torvalds
2020-07-27 22:43                 ` Yang Shi
2020-07-28  0:38                   ` Linus Torvalds
2020-07-28  0:13                 ` Yu Xu
2020-07-28 10:53                 ` Nicholas Piggin
2020-07-28 19:02                   ` Linus Torvalds
2020-07-28 22:53                     ` Nicholas Piggin
2020-07-29 13:58                       ` Michael Ellerman
2020-07-28  6:41             ` Yu Xu
2020-07-24  4:15 ` Andrew Morton [this message]
2020-07-24  4:15 ` [patch 03/15] vfs/xattr: mm/shmem: kernfs: release simple xattr entry in a right way Andrew Morton
2020-07-24  4:15 ` [patch 04/15] mm: initialize return of vm_insert_pages Andrew Morton
2020-07-24  4:15 ` [patch 05/15] mm/memcontrol: fix OOPS inside mem_cgroup_get_nr_swap_pages() Andrew Morton
2020-07-24  4:15 ` [patch 06/15] mm/memcg: fix refcount error while moving and swapping Andrew Morton
2020-07-24 13:41   ` Alex Shi
2020-07-24  4:15 ` [patch 07/15] mm: memcg/slab: fix memory leak at non-root kmem_cache destroy Andrew Morton
2020-07-24  4:15 ` [patch 08/15] mm/hugetlb: avoid hardcoding while checking if cma is enabled Andrew Morton
2020-07-24  4:15 ` [patch 09/15] khugepaged: fix null-pointer dereference due to race Andrew Morton
2020-07-24  4:15 ` [patch 10/15] mailmap: add entry for Mike Rapoport Andrew Morton
2020-07-24  4:15 ` [patch 11/15] squashfs: fix length field overlap check in metadata reading Andrew Morton
2020-07-24  4:15 ` [patch 12/15] scripts/decode_stacktrace: strip basepath from all paths Andrew Morton
2020-07-24  4:15 ` [patch 13/15] io-mapping: indicate mapping failure Andrew Morton
2020-07-24  4:15 ` [patch 14/15] MAINTAINERS: add KCOV section Andrew Morton
2020-07-24  4:15 ` [patch 15/15] scripts/gdb: fix lx-symbols 'gdb.error' while loading modules Andrew Morton
2020-07-28  1:19 ` mmotm 2020-07-27-18-18 uploaded Andrew Morton
2020-07-28  2:14   ` Stephen Rothwell
2020-07-28  3:22   ` mmotm 2020-07-27-18-18 uploaded (drivers/scsi/ufs/: SCSI_UFS_EXYNOS) Randy Dunlap
2020-07-28  8:23     ` Alim Akhtar
2020-07-28 12:33   ` mmotm 2020-07-27-18-18 uploaded (mm/page_alloc.c) Randy Dunlap
2020-07-28 21:55     ` Andrew Morton
2020-07-28 22:20       ` Stephen Rothwell
2020-07-28 22:31         ` Andrew Morton
2020-07-29 14:18           ` Michael S. Tsirkin
2020-07-29 14:38             ` David Hildenbrand
2020-07-29 16:14               ` David Hildenbrand
2020-07-29 17:29                 ` Randy Dunlap
2020-07-28 22:39       ` Randy Dunlap
2020-07-29  1:43         ` Nathan Chancellor
2020-07-29  1:44         ` Andrew Morton
2020-07-29  2:04           ` Randy Dunlap
2020-07-29 14:09           ` make oldconfig (Re: mmotm 2020-07-27-18-18 uploaded (mm/page_alloc.c)) Alexey Dobriyan
2020-07-31 23:46 ` mmotm 2020-07-31-16-45 uploaded Andrew Morton
2020-08-01  5:24   ` mmotm 2020-07-31-16-45 uploaded (drivers/staging/vc04_services/) Randy Dunlap

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