diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2020-02-26 01:46:12 +0530 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-03-11 07:51:15 +0100 |
| commit | c9343fc01d5459e01b7bf7c2277e789e85300884 (patch) | |
| tree | f3ca7683abaa995e4df72fb5336fb622fa2f55d9 /mm/hugetlb.c | |
| parent | a1f17db9b512e3c5ede5ecef031a08b14af601ee (diff) | |
mm: prevent get_user_pages() from overflowing page refcount
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>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[ 4.4.y backport notes:
Ajay: - Added local variable 'err' with-in follow_hugetlb_page()
from 2be7cfed995e, to resolve compilation error
- Added page_ref_count()
- Added missing refcount overflow checks on x86 and s390
(Vlastimil, thanks for this change)
Srivatsa: - Replaced call to get_page_foll() with try_get_page_foll() ]
Signed-off-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Signed-off-by: Ajay Kaher <akaher@vmware.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm/hugetlb.c')
| -rw-r--r-- | mm/hugetlb.c | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index fd932e7a25dd..3a1501e85483 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3886,6 +3886,7 @@ 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; @@ -3957,6 +3958,19 @@ 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_foll()' 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); @@ -3983,7 +3997,7 @@ same_page: *nr_pages = remainder; *position = vaddr; - return i ? i : -EFAULT; + return i ? i : err; } unsigned long hugetlb_change_protection(struct vm_area_struct *vma, |