mm/pagewalk.c: report holes in hugetlb ranges

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@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 8bd4afa..23a3e41 100644 (file)
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -188,8 +188,12 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end,
        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);