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)

Changed for 4.4/4.9 stable backport: - fix up conflict in the huge_pte_offset() call

Fixes: 1e25a271c8ac ("mincore: apply page table walker on do_mincore()") Signed-off-by: Jann Horn jannh@google.com --- Please apply this patch to <=4.9 stable trees instead of the original patch.

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

diff --git a/mm/pagewalk.c b/mm/pagewalk.c index 29f2f8b853ae..c2cbd2620169 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -142,8 +142,12 @@ 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); - 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);