From: Vlastimil Babka vbabka@suse.cz
The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") was backported to 4.19.y stable as commit d972ebbf42ba. The backport however missed that in 4.19, 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 --- arch/s390/mm/gup.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c index 2809d11c7a283..9b5b866d8adf1 100644 --- 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; }