On Thu, Jul 18, 2024 at 3:43 PM Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> wrote: > > * Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx> [240718 07:00]: > > On 7/16/24 10:29 AM, syzbot wrote: > > > Hello, > > > > dunno about the [crypto?] parts, sounds rather something for Suren or Liam > > or maybe it's due to some changes to gup? > > Yes, that crypto part is very odd. > > > > > > syzbot found the following issue on: > > > > > > HEAD commit: 3fe121b62282 Add linux-next specific files for 20240712 > > > git tree: linux-next > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1097ebed980000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=98dd8c4bab5cdce > > > dashboard link: https://syzkaller.appspot.com/bug?extid=4c882a4a0697c4a25364 > > > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40 > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11d611a5980000 > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13ce3259980000 > > > > > > Downloadable assets: > > > disk image: https://storage.googleapis.com/syzbot-assets/8c6fbf69718d/disk-3fe121b6.raw.xz > > > vmlinux: https://storage.googleapis.com/syzbot-assets/39fc7e43dfc1/vmlinux-3fe121b6.xz > > > kernel image: https://storage.googleapis.com/syzbot-assets/0a78e70e4b4e/bzImage-3fe121b6.xz > > > mounted in repro: https://storage.googleapis.com/syzbot-assets/66cfe5a679f2/mount_0.gz > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > Reported-by: syzbot+4c882a4a0697c4a25364@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > ================================================================== > > > BUG: KASAN: slab-use-after-free in handle_mm_fault+0x14f0/0x19a0 mm/memory.c:5842 > > > Read of size 8 at addr ffff88802c4719d0 by task syz-executor125/5235 > > > > > > CPU: 1 UID: 0 PID: 5235 Comm: syz-executor125 Not tainted 6.10.0-rc7-next-20240712-syzkaller #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024 > > > Call Trace: > > > <TASK> > > > __dump_stack lib/dump_stack.c:94 [inline] > > > dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 > > > print_address_description mm/kasan/report.c:377 [inline] > > > print_report+0x169/0x550 mm/kasan/report.c:488 > > > kasan_report+0x143/0x180 mm/kasan/report.c:601 > > > handle_mm_fault+0x14f0/0x19a0 mm/memory.c:5842 > > /* > * By the time we get here, we already hold the mm semaphore > * > * The mmap_lock may have been released depending on flags and our > * return value. See filemap_fault() and __folio_lock_or_retry(). > */ > > Somehow we are here without an RCU or mmap_lock held? I'm guessing we did enter handle_mm_fault() with mmap_lock held but __handle_mm_fault() dropped it before returning, see the comment for __handle_mm_fault(): /* * On entry, we hold either the VMA lock or the mmap_lock * (FAULT_FLAG_VMA_LOCK tells you which). If VM_FAULT_RETRY is set in * the result, the mmap_lock is not held on exit. See filemap_fault() * and __folio_lock_or_retry(). */ So after that there is nothing that guarantees VMA is not destroyed from under us and if (vma->vm_flags & VM_DROPPABLE) check is unsafe. Hillf's suggestion should fix this issue but we need to figure out how to make this path more robust. Currently it's very easy to make a similar mistake. Maybe a WARNING comment after __handle_mm_fault() that VMA might be unstable after that function and should not be used? > > > > faultin_page mm/gup.c:1194 [inline] > > /* > * mmap_lock must be held on entry. If @flags has FOLL_UNLOCKABLE but not > * FOLL_NOWAIT, the mmap_lock may be released. If it is, *@locked will be set > * to 0 and -EBUSY returned. > */ > > We should probably have a lockdep check there then? > > > > __get_user_pages+0x6ec/0x16a0 mm/gup.c:1493 > > > populate_vma_page_range+0x264/0x330 mm/gup.c:1932 > > > __mm_populate+0x27a/0x460 mm/gup.c:2035 > > /* > * __mm_populate - populate and/or mlock pages within a range of address space. > * > * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap > * flags. VMAs must be already marked with the desired vm_flags, and > * mmap_lock must not be held. > */ > > What ensures the vma doesn't go away then? - I guess nothing, because it > went away. > > I don't get it.. __mm_populate() must NOT have the mmap_lock, but > faultin_page() must hold the mmap_lock... > > > > mm_populate include/linux/mm.h:3429 [inline] > > > vm_mmap_pgoff+0x2c3/0x3d0 mm/util.c:593 > > > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > > > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 > > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > RIP: 0033:0x7f093ce17fe9 > > > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 1d 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48 > > > RSP: 002b:00007f093cd9e158 EFLAGS: 00000246 ORIG_RAX: 0000000000000009 > > > RAX: ffffffffffffffda RBX: 00007f093ce9f4b8 RCX: 00007f093ce17fe9 > > > RDX: 0000000000000002 RSI: 0000000000b36000 RDI: 0000000020000000 > > > RBP: 00007f093ce9f4b0 R08: 00000000ffffffff R09: 0000000000000000 > > > R10: 0000000000008031 R11: 0000000000000246 R12: 00007f093ce9f4bc > > > R13: 000000000000006e R14: 00007ffe8008cc30 R15: 00007ffe8008cd18 > > > </TASK> > > > > > > Allocated by task 5235: > ... > > > > > > > Freed by task 5237: > > > kasan_save_stack mm/kasan/common.c:47 [inline] > > > kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 > > > kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:579 > > > poison_slab_object+0xe0/0x150 mm/kasan/common.c:240 > > > __kasan_slab_free+0x37/0x60 mm/kasan/common.c:256 > > > kasan_slab_free include/linux/kasan.h:184 [inline] > > > slab_free_hook mm/slub.c:2252 [inline] > > > slab_free mm/slub.c:4473 [inline] > > > kmem_cache_free+0x145/0x350 mm/slub.c:4548 > > > rcu_do_batch kernel/rcu/tree.c:2569 [inline] > > > rcu_core+0xafd/0x1830 kernel/rcu/tree.c:2843 > > This seems right. RCU freeing of a vma here, so that's okay. > > > > handle_softirqs+0x2c4/0x970 kernel/softirq.c:554 > > > __do_softirq kernel/softirq.c:588 [inline] > > > invoke_softirq kernel/softirq.c:428 [inline] > > > __irq_exit_rcu+0xf4/0x1c0 kernel/softirq.c:637 > > > irq_exit_rcu+0x9/0x30 kernel/softirq.c:649 > > > instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline] > > > sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1043 > > > asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702 > > > > > > Last potentially related work creation: > > Also fine. > > > > kasan_save_stack+0x3f/0x60 mm/kasan/common.c:47 > > > __kasan_record_aux_stack+0xac/0xc0 mm/kasan/generic.c:541 > > > __call_rcu_common kernel/rcu/tree.c:3106 [inline] > > > call_rcu+0x167/0xa70 kernel/rcu/tree.c:3210 > > > remove_vma mm/mmap.c:189 [inline] > > > remove_mt mm/mmap.c:2415 [inline] > > > do_vmi_align_munmap+0x155c/0x18c0 mm/mmap.c:2758 > > > do_vmi_munmap+0x261/0x2f0 mm/mmap.c:2830 > > > mmap_region+0x72f/0x2090 mm/mmap.c:2881 > > > do_mmap+0x8f9/0x1010 mm/mmap.c:1468 > > > vm_mmap_pgoff+0x1dd/0x3d0 mm/util.c:588 > > > ksys_mmap_pgoff+0x544/0x720 mm/mmap.c:1514 > > > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > > > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 > > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > > > > The buggy address belongs to the object at ffff88802c4719b0 > > > which belongs to the cache vm_area_struct of size 184 > > ... >
