On Fri, Jun 17, 2022 at 5:14 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Fri, Jun 17, 2022 at 04:52:56PM -0700, Andrew Morton wrote: > > On Fri, 17 Jun 2022 00:04:23 -0700 syzbot <syzbot+4d875b4d2e2b60bae9b4@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > Hello, > > > > > > syzbot found the following issue on: > > > > > > HEAD commit: c6d7e3b385f1 Add linux-next specific files for 20220616 > > > git tree: linux-next > > > console output: https://syzkaller.appspot.com/x/log.txt?x=10d9fb1bf00000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=9d495405e4a98620 > > > dashboard link: https://syzkaller.appspot.com/bug?extid=4d875b4d2e2b60bae9b4 > > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > Reported-by: syzbot+4d875b4d2e2b60bae9b4@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > ================================================================== > > > BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:71 [inline] > > > BUG: KASAN: null-ptr-deref in test_bit include/asm-generic/bitops/instrumented-non-atomic.h:134 [inline] > > > BUG: KASAN: null-ptr-deref in hugepage_vma_check+0x8e/0x750 mm/huge_memory.c:82 > > > Read of size 8 at addr 00000000000005a8 by task syz-executor.5/21978 > > > > vma->vm_mm is NULL in show_smap->hugepage_vma_check(). > > > > Perhaps m_start() should be checking the mm after taking > > mmap_read_lock() instead of before? > > > > Matthew, you mucked with it last ;) Can you please take a look? > > I think this is Yang Shi's fault. The last patch in that series which > touches this area does: > > seq_printf(m, "THPeligible: %d\n", > - hugepage_vma_check(vma, vma->vm_flags, true)); > + hugepage_vma_check(vma, vma->vm_flags, true, false)); > > and hugepage_vma_check() does: > > if ((vm_flags & VM_NOHUGEPAGE) || > test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) > return false; > > Before those patches, it calls transparent_hugepage_active() which > does not (afaict) touch vma->vm_mm. No, transparent_hugepage_active() also could touch vma->vm_mm. The above code was transhuge_vma_enabled() called by transparent_hugepage_active() before my patch, my patch just open-coded it. But hugepage_vma_check() does check vma in different order from transparent_hugepage_active(), so the old code may not reach it at all. And I don't think the mm could go away since it is pinned, but the returned vma may not belong to this mm, for example, gate vma which doesn't have a mm. Its size is PAGE_SIZE, so the old code returns earlier before touching mm. One possible solution is to move vma size check before touching mm, like: diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 2e2a8b5bc567..1a9f15a89091 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -73,6 +73,16 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags, bool smaps, bool in_pf) { + /* + * Check alignment for file vma and size for both file and anon vma. + * + * Skip the check for page fault. Huge fault does the check in fault + * handlers. And this check is not suitable for huge PUD fault. + */ + if (!in_pf && + !transhuge_vma_suitable(vma, (vma->vm_end - HPAGE_PMD_SIZE))) + return false; + /* * Explicitly disabled through madvise or prctl, or some * architectures may disable THP for some mappings, for @@ -99,16 +109,6 @@ bool hugepage_vma_check(struct vm_area_struct *vma, if (vm_flags & VM_NO_KHUGEPAGED) return false; - /* - * Check alignment for file vma and size for both file and anon vma. - * - * Skip the check for page fault. Huge fault does the check in fault - * handlers. And this check is not suitable for huge PUD fault. - */ - if (!in_pf && - !transhuge_vma_suitable(vma, (vma->vm_end - HPAGE_PMD_SIZE))) - return false; - /* * Enabled via shmem mount options or sysfs settings. * Must be done before hugepage flags check since shmem has its Or we may have to check gate vma explicitly. > > I haven't been paying attention to that patch series, so I don't have > a constructive suggestion for how to fix. > > > > CPU: 0 PID: 21978 Comm: syz-executor.5 Not tainted 5.19.0-rc2-next-20220616-syzkaller #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > > Call Trace: > > > <TASK> > > > __dump_stack lib/dump_stack.c:88 [inline] > > > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 > > > kasan_report+0xbe/0x1f0 mm/kasan/report.c:495 > > > check_region_inline mm/kasan/generic.c:183 [inline] > > > kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189 > > > instrument_atomic_read include/linux/instrumented.h:71 [inline] > > > test_bit include/asm-generic/bitops/instrumented-non-atomic.h:134 [inline] > > > hugepage_vma_check+0x8e/0x750 mm/huge_memory.c:82 > > > show_smap+0x1c6/0x470 fs/proc/task_mmu.c:866 > > > traverse.part.0+0xcf/0x5f0 fs/seq_file.c:111 > > > traverse fs/seq_file.c:101 [inline] > > > seq_read_iter+0x90f/0x1280 fs/seq_file.c:195 > > > seq_read+0x337/0x4b0 fs/seq_file.c:162 > > > do_loop_readv_writev fs/read_write.c:763 [inline] > > > do_loop_readv_writev fs/read_write.c:750 [inline] > > > do_iter_read+0x4f8/0x750 fs/read_write.c:805 > > > vfs_readv+0xe5/0x150 fs/read_write.c:923 > > > do_preadv fs/read_write.c:1015 [inline] > > > __do_sys_preadv fs/read_write.c:1065 [inline] > > > __se_sys_preadv fs/read_write.c:1060 [inline] > > > __x64_sys_preadv+0x22b/0x310 fs/read_write.c:1060 > > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > > > entry_SYSCALL_64_after_hwframe+0x46/0xb0 > > > RIP: 0033:0x7f5c1d889109 > > > Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 > > > RSP: 002b:00007f5c1ea69168 EFLAGS: 00000246 ORIG_RAX: 0000000000000127 > > > RAX: ffffffffffffffda RBX: 00007f5c1d99bf60 RCX: 00007f5c1d889109 > > > RDX: 0000000000000001 RSI: 00000000200006c0 RDI: 0000000000000005 > > > RBP: 00007f5c1d8e305d R08: 0000000000000000 R09: 0000000000000000 > > > R10: 00000000fffffffe R11: 0000000000000246 R12: 0000000000000000 > > > R13: 00007ffd8514b43f R14: 00007f5c1ea69300 R15: 0000000000022000 > > > </TASK> > > > ================================================================== > > > > > > > > > --- > > > This report is generated by a bot. It may contain errors. > > > See https://goo.gl/tpsmEJ for more information about syzbot. > > > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > > > > > syzbot will keep track of this issue. See: > > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
