From 246c320a8cfe0b11d81a4af38fa9985ef0cc9a4c Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Thu, 23 Jul 2020 21:15:11 -0700 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] Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap") Reported-by: Jann Horn Signed-off-by: Kirill A. Shutemov Signed-off-by: Andrew Morton Reviewed-by: Yang Shi Acked-by: Vlastimil Babka Cc: Oleg Nesterov Cc: Matthew Wilcox Cc: [4.20+] Link: http://lkml.kernel.org/r/20200709105309.42495-1-kirill.shutemov@linux.intel.com Signed-off-by: Linus Torvalds --- mm/mmap.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'mm') diff --git a/mm/mmap.c b/mm/mmap.c index 59a4682ebf3f..8c7ca737a19b 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2620,7 +2620,7 @@ static void unmap_region(struct mm_struct *mm, * 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_struct *mm, struct vm_area_struct *vma, /* 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, unsigned long start, size_t len, } /* 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); -- cgit v1.2.3