On Sun, Aug 28, 2016 at 12:42:21PM +0200, Dmitry Vyukov wrote: > Hello, > > I've git the following use-after-free in collapse_huge_page while > running syzkaller fuzzer. It is in khugepaged, so not reproducible. On > commit 61c04572de404e52a655a36752e696bbcb483cf5 (Aug 25). > > ================================================================== > BUG: KASAN: use-after-free in collapse_huge_page+0x28b1/0x3500 at addr > ffff88006c731388 > Read of size 8 by task khugepaged/1327 > CPU: 0 PID: 1327 Comm: khugepaged Not tainted 4.8.0-rc3+ #33 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > ffffffff884b8280 ffff88003c207920 ffffffff82d1b239 ffffffff89ec1520 > fffffbfff1097050 ffff88003e94c700 ffff88006c731300 ffff88006c7313c0 > 0000000000000000 ffff88003c207b88 ffff88003c207948 ffffffff817da1fc > Call Trace: > [<ffffffff817da82e>] __asan_report_load8_noabort+0x3e/0x40 > mm/kasan/report.c:322 > [<ffffffff817ff651>] collapse_huge_page+0x28b1/0x3500 mm/khugepaged.c:1004 Okay, I think the patch below should do the trick. Build tested only. Andrea, Ebru, could you re-check if it's reasonable. >From bc6c3589a3da75fabd6d440cce3c8ea23b69c2e5 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Date: Mon, 29 Aug 2016 15:32:50 +0300 Subject: [PATCH] khugepaged: fix use-after-free in collapse_huge_page() hugepage_vma_revalidate() tries to re-check if we still should try to collapse small pages into huge one after the re-acquiring mmap_sem. The problem Dmitry Vyukov reported[1] is that the vma found by hugepage_vma_revalidate() can be suitable for huge pages, but not the same vma we had before dropping mmap_sem. And dereferencing original vma can lead to fun results.. Let's use vma hugepage_vma_revalidate() found instead of assuming it's the same as what we had before the lock was dropped. [1] http://lkml.kernel.org/r/CACT4Y+Z3gigBvhca9kRJFcjX0G70V_nRhbwKBU+yGoESBDKi9Q@xxxxxxxxxxxxxx Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> --- mm/khugepaged.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 79c52d0061af..3c8253f160ca 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -838,7 +838,8 @@ static bool hugepage_vma_check(struct vm_area_struct *vma) * value (scan code). */ -static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address) +static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, + struct vm_area_struct **vmap) { struct vm_area_struct *vma; unsigned long hstart, hend; @@ -846,7 +847,7 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address) if (unlikely(khugepaged_test_exit(mm))) return SCAN_ANY_PROCESS; - vma = find_vma(mm, address); + *vmap = vma = find_vma(mm, address); if (!vma) return SCAN_VMA_NULL; @@ -898,13 +899,13 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */ if (ret & VM_FAULT_RETRY) { down_read(&mm->mmap_sem); - if (hugepage_vma_revalidate(mm, address)) { + if (hugepage_vma_revalidate(mm, address, &vma)) { /* vma is no longer available, don't continue to swapin */ trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); return false; } /* check if the pmd is still valid */ - if (mm_find_pmd(mm, address) != pmd) + if (mm_find_pmd(mm, address) != pmd || vma != fe.vma) return false; } if (ret & VM_FAULT_ERROR) { @@ -923,7 +924,6 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, static void collapse_huge_page(struct mm_struct *mm, unsigned long address, struct page **hpage, - struct vm_area_struct *vma, int node, int referenced) { pmd_t *pmd, _pmd; @@ -933,6 +933,7 @@ static void collapse_huge_page(struct mm_struct *mm, spinlock_t *pmd_ptl, *pte_ptl; int isolated = 0, result = 0; struct mem_cgroup *memcg; + struct vm_area_struct *vma; unsigned long mmun_start; /* For mmu_notifiers */ unsigned long mmun_end; /* For mmu_notifiers */ gfp_t gfp; @@ -961,7 +962,7 @@ static void collapse_huge_page(struct mm_struct *mm, } down_read(&mm->mmap_sem); - result = hugepage_vma_revalidate(mm, address); + result = hugepage_vma_revalidate(mm, address, &vma); if (result) { mem_cgroup_cancel_charge(new_page, memcg, true); up_read(&mm->mmap_sem); @@ -994,7 +995,7 @@ static void collapse_huge_page(struct mm_struct *mm, * handled by the anon_vma lock + PG_lock. */ down_write(&mm->mmap_sem); - result = hugepage_vma_revalidate(mm, address); + result = hugepage_vma_revalidate(mm, address, &vma); if (result) goto out; /* check if the pmd is still valid */ @@ -1202,7 +1203,7 @@ out_unmap: if (ret) { node = khugepaged_find_target_node(); /* collapse_huge_page will return with the mmap_sem released */ - collapse_huge_page(mm, address, hpage, vma, node, referenced); + collapse_huge_page(mm, address, hpage, node, referenced); } out: trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>