linux-kernel - [PATCH STABLE 4.19] mm, gup: add missing refcount overflow checks on s390

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Message-Id: <20191129090351.3507-4-vbabka@suse.cz>
Date:   Fri, 29 Nov 2019 10:03:51 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     stable@...r.kernel.org
Cc:     Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Ajay Kaher <akaher@...are.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH STABLE 4.19] 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 4.19.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@...e.cz>
---
 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 2809d11c7a28..9b5b866d8adf 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;
 	}
-- 
2.24.0