From 443c46f3f30699b85ce2e1e4fd5464ae952bc028 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 19 Apr 2019 15:29:22 +0800 Subject: [PATCH] mm: prevent get_user_pages() from overflowing page refcount mainline inclusion from mainline-5.1-rc5 commit 8fde12ca79af category: bugfix bugzilla: NA CVE: NA ------------------------------------------------- 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. Conflicts: mm/gup.c Reported-by: Jann Horn Acked-by: Matthew Wilcox Cc: stable@kernel.org Signed-off-by: Linus Torvalds Signed-off-by: zhong jiang Reviewed-by: Jing Xiangfeng Signed-off-by: Yang Yingliang --- mm/gup.c | 45 ++++++++++++++++++++++++++++++++++----------- mm/hugetlb.c | 13 +++++++++++++ 2 files changed, 47 insertions(+), 11 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 2c0eda934e14..b91c47fc9157 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -153,7 +153,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, } if (flags & FOLL_GET) { - get_page(page); + if (unlikely(!try_get_page(page))) { + page = ERR_PTR(-ENOMEM); + goto out; + } /* drop the pgmap reference now that we hold the page */ if (pgmap) { @@ -296,7 +299,10 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, if (pmd_trans_unstable(pmd)) ret = -EBUSY; } else { - get_page(page); + if (unlikely(!try_get_page(page))) { + spin_unlock(ptl); + return ERR_PTR(-ENOMEM); + } spin_unlock(ptl); lock_page(page); ret = split_huge_page(page); @@ -480,7 +486,10 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address, if (is_device_public_page(*page)) goto unmap; } - get_page(*page); + if (unlikely(!try_get_page(*page))) { + ret = -ENOMEM; + goto unmap; + } out: ret = 0; unmap: @@ -1368,6 +1377,20 @@ static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages) } } +/* + * Return the compund head page with ref appropriately incremented, + * or NULL if that failed. + */ +static inline struct page *try_get_compound_head(struct page *page, int refs) +{ + struct page *head = compound_head(page); + if (WARN_ON_ONCE(page_ref_count(head) < 0)) + return NULL; + if (unlikely(!page_cache_add_speculative(head, refs))) + return NULL; + return head; +} + #ifdef CONFIG_ARCH_HAS_PTE_SPECIAL static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) @@ -1402,9 +1425,9 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); - head = compound_head(page); - if (!page_cache_get_speculative(head)) + head = try_get_compound_head(page, 1); + if (!head) goto pte_unmap; if (unlikely(pte_val(pte) != pte_val(*ptep))) { @@ -1543,8 +1566,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - head = compound_head(pmd_page(orig)); - if (!page_cache_add_speculative(head, refs)) { + head = try_get_compound_head(pmd_page(orig), refs); + if (!head) { *nr -= refs; return 0; } @@ -1581,8 +1604,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - head = compound_head(pud_page(orig)); - if (!page_cache_add_speculative(head, refs)) { + head = try_get_compound_head(pud_page(orig), refs); + if (!head) { *nr -= refs; return 0; } @@ -1618,8 +1641,8 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - head = compound_head(pgd_page(orig)); - if (!page_cache_add_speculative(head, refs)) { + head = try_get_compound_head(pgd_page(orig), refs); + if (!head) { *nr -= refs; return 0; } diff --git a/mm/hugetlb.c b/mm/hugetlb.c index e0d9a2f92b5e..5ba9524376df 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4324,6 +4324,19 @@ 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); -- GitLab