mm, gup: add missing refcount overflow checks on s390

The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from
overflowing page refcount") was backported to 4.14.y stable as commit
04198de24771. The backport however missed that in 4.14, there are several
arch-specific gup.c versions with fast gup implementations, so these do not
prevent refcount overflow.

This stable-only commit fixes the s390 version, and is based on the backport in
SUSE SLES/openSUSE 4.12-based kernels.

The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely
the known overflow scenario based on FUSE, which needs 140GB of RAM, is a
problem for those architectures, and I don't feel confident enough to patch
them.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
index 05c8abd864f1df27d9c3b6a8aba58964fd17222e..9bce54eac0b079e09bc0e5319005735804262a9f 100644 (file)
--- a/arch/s390/mm/gup.c
+++ b/arch/s390/mm/gup.c
@@ -39,7 +39,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
                VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
                page = pte_page(pte);
                head = compound_head(page);
-               if (!page_cache_get_speculative(head))
+               if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0)
+                   || !page_cache_get_speculative(head)))
                        return 0;
                if (unlikely(pte_val(pte) != pte_val(*ptep))) {
                        put_page(head);
@@ -77,7 +78,8 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
                refs++;
        } while (addr += PAGE_SIZE, addr != end);
 
-       if (!page_cache_add_speculative(head, refs)) {
+       if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0)
+           || !page_cache_add_speculative(head, refs))) {
                *nr -= refs;
                return 0;
        }
@@ -151,7 +153,8 @@ static int gup_huge_pud(pud_t *pudp, pud_t pud, unsigned long addr,
                refs++;
        } while (addr += PAGE_SIZE, addr != end);
 
-       if (!page_cache_add_speculative(head, refs)) {
+       if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0)
+           || !page_cache_add_speculative(head, refs))) {
                *nr -= refs;
                return 0;
        }