From 373c4557d2aa362702c4c2d41288fb1e54990b7c Mon Sep 17 00:00:00 2001
From: Jann Horn <jannh@google.com>
Date: Tue, 14 Nov 2017 01:03:44 +0100
Subject: [PATCH] mm/pagewalk.c: report holes in hugetlb ranges
Git-commit: 373c4557d2aa362702c4c2d41288fb1e54990b7c
Patch-mainline: v4.15-rc1
References: bnc#1069996, CVE-2017-16994
This matters at least for the mincore syscall, which will otherwise copy
uninitialized memory from the page allocator to userspace. It is
probably also a correctness error for /proc/$pid/pagemap, but I haven't
tested that.
Removing the `walk->hugetlb_entry` condition in walk_hugetlb_range() has
no effect because the caller already checks for that.
This only reports holes in hugetlb ranges to callers who have specified
a hugetlb_entry callback.
This issue was found using an AFL-based fuzzer.
V2: - don't crash on ->pte_hole==NULL (Andrew Morton)
- add Cc stable (Andrew Morton)
Fixes: 1e25a271c8ac ("mincore: apply page table walker on do_mincore()")
Signed-off-by: Jann Horn <jannh@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
---
mm/pagewalk.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -186,8 +186,12 @@ static int walk_hugetlb_range(unsigned l
do {
next = hugetlb_entry_end(h, addr, end);
pte = huge_pte_offset(walk->mm, addr & hmask);
- if (pte && walk->hugetlb_entry)
+
+ if (pte)
err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
+ else if (walk->pte_hole)
+ err = walk->pte_hole(addr, next, walk);
+
if (err)
break;
} while (addr = next, addr != end);