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authorLinus Torvalds <torvalds@linux-foundation.org>2019-04-11 10:49:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-04-14 10:00:04 -0700
commit8fde12ca79aff9b5ba951fce1a2641901b8d8e64 (patch)
tree23ee93c180e690ccd12257fb677fa9b40e1be53a /mm/hugetlb.c
parent88b1a17dfc3ed7728316478fae0f5ad508f50397 (diff)
mm: prevent get_user_pages() from overflowing page refcount
If the page refcount wraps around past zero, it will be freed while there are still four billion references to it. One of the possible avenues for an attacker to try to make this happen is by doing direct IO on a page multiple times. This patch makes get_user_pages() refuse to take a new page reference if there are already more than two billion references to the page. Reported-by: Jann Horn <jannh@google.com> Acked-by: Matthew Wilcox <willy@infradead.org> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/hugetlb.c')
-rw-r--r--mm/hugetlb.c13
1 files changed, 13 insertions, 0 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8dfdffc34a99..c220315dc533 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4298,6 +4298,19 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT;
page = pte_page(huge_ptep_get(pte));
+
+ /*
+ * Instead of doing 'try_get_page()' below in the same_page
+ * loop, just check the count once here.
+ */
+ if (unlikely(page_count(page) <= 0)) {
+ if (pages) {
+ spin_unlock(ptl);
+ remainder = 0;
+ err = -ENOMEM;
+ break;
+ }
+ }
same_page:
if (pages) {
pages[i] = mem_map_offset(page, pfn_offset);