From: Eric Biggers <ebiggers@google.com>

Date: Fri, 25 Aug 2017 15:55:39 -0700

Subject: [PATCH] mm/madvise.c: fix freeing of locked page with MADV_FREE

References: bnc#1060662

Patch-mainline: 4.12.10

Git-commit: 263630e8d176d87308481ebdcd78ef9426739c6b

commit 263630e8d176d87308481ebdcd78ef9426739c6b upstream.

If madvise(..., MADV_FREE) split a transparent hugepage, it called

put_page() before unlock_page().

This was wrong because put_page() can free the page, e.g. if a

concurrent madvise(..., MADV_DONTNEED) has removed it from the memory

mapping. put_page() then rightfully complained about freeing a locked

page.

Fix this by moving the unlock_page() before put_page().

This bug was found by syzkaller, which encountered the following splat:

    BUG: Bad page state in process syzkaller412798  pfn:1bd800

    page:ffffea0006f60000 count:0 mapcount:0 mapping:          (null) index:0x20a00

    flags: 0x200000000040019(locked|uptodate|dirty|swapbacked)

    raw: 0200000000040019 0000000000000000 0000000000020a00 00000000ffffffff

    raw: ffffea0006f60020 ffffea0006f60020 0000000000000000 0000000000000000

    page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set

    bad because of flags: 0x1(locked)

    Modules linked in:

    CPU: 1 PID: 3037 Comm: syzkaller412798 Not tainted 4.13.0-rc5+ #35

    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

    Call Trace:

     __dump_stack lib/dump_stack.c:16 [inline]

     dump_stack+0x194/0x257 lib/dump_stack.c:52

     bad_page+0x230/0x2b0 mm/page_alloc.c:565

     free_pages_check_bad+0x1f0/0x2e0 mm/page_alloc.c:943

     free_pages_check mm/page_alloc.c:952 [inline]

     free_pages_prepare mm/page_alloc.c:1043 [inline]

     free_pcp_prepare mm/page_alloc.c:1068 [inline]

     free_hot_cold_page+0x8cf/0x12b0 mm/page_alloc.c:2584

     __put_single_page mm/swap.c:79 [inline]

     __put_page+0xfb/0x160 mm/swap.c:113

     put_page include/linux/mm.h:814 [inline]

     madvise_free_pte_range+0x137a/0x1ec0 mm/madvise.c:371

     walk_pmd_range mm/pagewalk.c:50 [inline]

     walk_pud_range mm/pagewalk.c:108 [inline]

     walk_p4d_range mm/pagewalk.c:134 [inline]

     walk_pgd_range mm/pagewalk.c:160 [inline]

     __walk_page_range+0xc3a/0x1450 mm/pagewalk.c:249

     walk_page_range+0x200/0x470 mm/pagewalk.c:326

     madvise_free_page_range.isra.9+0x17d/0x230 mm/madvise.c:444

     madvise_free_single_vma+0x353/0x580 mm/madvise.c:471

     madvise_dontneed_free mm/madvise.c:555 [inline]

     madvise_vma mm/madvise.c:664 [inline]

     SYSC_madvise mm/madvise.c:832 [inline]

     SyS_madvise+0x7d3/0x13c0 mm/madvise.c:760

     entry_SYSCALL_64_fastpath+0x1f/0xbe

Here is a C reproducer:

    #define _GNU_SOURCE

    #include <pthread.h>

    #include <sys/mman.h>

    #include <unistd.h>

    #define MADV_FREE	8

    #define PAGE_SIZE	4096

    static void *mapping;

    static const size_t mapping_size = 0x1000000;

    static void *madvise_thrproc(void *arg)

    {

        madvise(mapping, mapping_size, (long)arg);

    }

    int main(void)

    {

        pthread_t t[2];

        for (;;) {

            mapping = mmap(NULL, mapping_size, PROT_WRITE,

                           MAP_POPULATE|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);

            munmap(mapping + mapping_size / 2, PAGE_SIZE);

            pthread_create(&t[0], 0, madvise_thrproc, (void*)MADV_DONTNEED);

            pthread_create(&t[1], 0, madvise_thrproc, (void*)MADV_FREE);

            pthread_join(t[0], NULL);

            pthread_join(t[1], NULL);

            munmap(mapping, mapping_size);

        }

    }

Note: to see the splat, CONFIG_TRANSPARENT_HUGEPAGE=y and

CONFIG_DEBUG_VM=y are needed.

Google Bug Id: 64696096

Link: http://lkml.kernel.org/r/20170823205235.132061-1-ebiggers3@gmail.com

Fixes: 854e9ed09ded ("mm: support madvise(MADV_FREE)")

Signed-off-by: Eric Biggers <ebiggers@google.com>

Acked-by: David Rientjes <rientjes@google.com>

Acked-by: Minchan Kim <minchan@kernel.org>

Acked-by: Michal Hocko <mhocko@suse.com>

Cc: Dmitry Vyukov <dvyukov@google.com>

Cc: Hugh Dickins <hughd@google.com>

Cc: Andrea Arcangeli <aarcange@redhat.com>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Jiri Slaby <jslaby@suse.cz>

---

 mm/madvise.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/madvise.c b/mm/madvise.c

index 75d2cffbe61d..fc6bfbe19a16 100644

--- a/mm/madvise.c

+++ b/mm/madvise.c

@@ -368,8 +368,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,

 				pte_offset_map_lock(mm, pmd, addr, &ptl);

 				goto out;

 			}

-			put_page(page);

 			unlock_page(page);

+			put_page(page);

 			pte = pte_offset_map_lock(mm, pmd, addr, &ptl);

 			pte--;

 			addr -= PAGE_SIZE;

-- 

2.14.2