linux-kernel - [PATCH 4.13 28/35] mm/pagewalk.c: report holes in hugetlb ranges

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Message-Id: <20171122101139.489140219@linuxfoundation.org>
Date:   Wed, 22 Nov 2017 11:12:22 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jann Horn <jannh@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.13 28/35] mm/pagewalk.c: report holes in hugetlb ranges

4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jann Horn <jannh@...gle.com>

commit 373c4557d2aa362702c4c2d41288fb1e54990b7c upstream.

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@...gle.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/pagewalk.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -187,8 +187,12 @@ static int walk_hugetlb_range(unsigned l
 	do {
 		next = hugetlb_entry_end(h, addr, end);
 		pte = huge_pte_offset(walk->mm, addr & hmask, sz);
-		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);