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mm: prevent get_user_pages() from overflowing page refcount

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commit 8fde12ca79aff9b5ba951fce1a2641901b8d8e64 upstream.

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 4.9:
 - Add the "err" variable in follow_hugetlb_page()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Linus Torvalds 2019-04-11 10:49:19 -07:00 committed by Greg Kroah-Hartman
parent 26c02ad801
commit 2ed768cfd8
2 changed files with 49 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
mm/gup.c
View File

@ -153,7 +153,10 @@ retry:
}
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) {
@ -292,7 +295,10 @@ struct page *follow_page_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);
@ -348,7 +354,10 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
goto unmap;
*page = pte_page(*pte);
}
get_page(*page);
if (unlikely(!try_get_page(*page))) {
ret = -ENOMEM;
goto unmap;
}
out:
ret = 0;
unmap:
@ -1231,6 +1240,20 @@ struct page *get_dump_page(unsigned long addr)
*/
#ifdef CONFIG_HAVE_GENERIC_RCU_GUP
/*
* 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 __HAVE_ARCH_PTE_SPECIAL
static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
int write, struct page **pages, int *nr)
@ -1263,9 +1286,9 @@ 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))) {
@ -1321,8 +1344,8 @@ 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;
}
@ -1355,8 +1378,8 @@ 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;
}
@ -1390,8 +1413,8 @@ 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;
}

16
mm/hugetlb.c
View File

@ -3984,6 +3984,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long vaddr = *position;
unsigned long remainder = *nr_pages;
struct hstate *h = hstate_vma(vma);
int err = -EFAULT;
while (vaddr < vma->vm_end && remainder) {
pte_t *pte;
@ -4055,6 +4056,19 @@ 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);
@ -4081,7 +4095,7 @@ same_page:
*nr_pages = remainder;
*position = vaddr;
return i ? i : -EFAULT;
return i ? i : err;
}
#ifndef __HAVE_ARCH_FLUSH_HUGETLB_TLB_RANGE