> On Sep 20, 2024, at 3:13 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > On Fri, 2024-09-20 at 18:51 +0000, Chuck Lever III wrote: >> >>> On Sep 19, 2024, at 10:57 PM, NeilBrown <neilb@xxxxxxx> wrote: >>> >>> On Thu, 19 Sep 2024, Jeff Layton wrote: >>>> On Wed, 2024-09-18 at 08:38 -0700, syzbot wrote: >>>>> Hello, >>>>> >>>>> syzbot found the following issue on: >>>>> >>>>> HEAD commit: a430d95c5efa Merge tag 'lsm-pr-20240911' of git://git.kern.. >>>>> git tree: upstream >>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=17c7469f980000 >>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=a69c66e868285a9d >>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=24cd636199753ac5e0ca >>>>> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 >>>>> >>>>> Unfortunately, I don't have any reproducer for this issue yet. >>>>> >>>>> Downloadable assets: >>>>> disk image: https://storage.googleapis.com/syzbot-assets/7f3aff905e91/disk-a430d95c.raw.xz >>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/a468ce8431f0/vmlinux-a430d95c.xz >>>>> kernel image: https://storage.googleapis.com/syzbot-assets/80d4f1150155/bzImage-a430d95c.xz >>>>> >>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit: >>>>> Reported-by: syzbot+24cd636199753ac5e0ca@xxxxxxxxxxxxxxxxxxxxxxxxx >>>>> >>>>> svc: failed to register nfsdv3 RPC service (errno 111). >>>>> svc: failed to register nfsaclv3 RPC service (errno 111). >>>>> ================================================================== >>>>> BUG: KASAN: slab-use-after-free in list_add include/linux/list.h:169 [inline] >>>>> BUG: KASAN: slab-use-after-free in rhashtable_walk_enter+0x333/0x370 lib/rhashtable.c:684 >>>>> Read of size 8 at addr ffff8880773fa010 by task syz.2.11924/9970 >>>>> >>>>> CPU: 0 UID: 0 PID: 9970 Comm: syz.2.11924 Not tainted 6.11.0-syzkaller-02574-ga430d95c5efa #0 >>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024 >>>>> Call Trace: >>>>> <TASK> >>>>> __dump_stack lib/dump_stack.c:93 [inline] >>>>> dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:119 >>>>> print_address_description mm/kasan/report.c:377 [inline] >>>>> print_report+0xc3/0x620 mm/kasan/report.c:488 >>>>> kasan_report+0xd9/0x110 mm/kasan/report.c:601 >>>>> list_add include/linux/list.h:169 [inline] >>>>> rhashtable_walk_enter+0x333/0x370 lib/rhashtable.c:684 >>>>> rhltable_walk_enter include/linux/rhashtable.h:1262 [inline] >>>>> __nfsd_file_cache_purge+0xad/0x490 fs/nfsd/filecache.c:805 >>>>> nfsd_file_cache_shutdown+0xcf/0x480 fs/nfsd/filecache.c:897 >>>>> nfsd_shutdown_generic fs/nfsd/nfssvc.c:329 [inline] >>>>> nfsd_shutdown_generic fs/nfsd/nfssvc.c:323 [inline] >>>>> nfsd_startup_net fs/nfsd/nfssvc.c:444 [inline] >>>>> nfsd_svc+0x6d4/0x970 fs/nfsd/nfssvc.c:817 >>>>> nfsd_nl_threads_set_doit+0x52c/0xbc0 fs/nfsd/nfsctl.c:1714 >>>>> genl_family_rcv_msg_doit+0x202/0x2f0 net/netlink/genetlink.c:1115 >>>>> genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] >>>>> genl_rcv_msg+0x565/0x800 net/netlink/genetlink.c:1210 >>>>> netlink_rcv_skb+0x165/0x410 net/netlink/af_netlink.c:2550 >>>>> genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219 >>>>> netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline] >>>>> netlink_unicast+0x53c/0x7f0 net/netlink/af_netlink.c:1357 >>>>> netlink_sendmsg+0x8b8/0xd70 net/netlink/af_netlink.c:1901 >>>>> sock_sendmsg_nosec net/socket.c:730 [inline] >>>>> __sock_sendmsg net/socket.c:745 [inline] >>>>> ____sys_sendmsg+0x9ae/0xb40 net/socket.c:2603 >>>>> ___sys_sendmsg+0x135/0x1e0 net/socket.c:2657 >>>>> __sys_sendmsg+0x117/0x1f0 net/socket.c:2686 >>>>> do_syscall_x64 arch/x86/entry/common.c:52 [inline] >>>>> do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83 >>>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f >>>>> RIP: 0033:0x7fd947f7def9 >>>>> 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 a8 ff ff ff f7 d8 64 89 01 48 >>>>> RSP: 002b:00007fd948e38038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e >>>>> RAX: ffffffffffffffda RBX: 00007fd948135f80 RCX: 00007fd947f7def9 >>>>> RDX: 0000000000000004 RSI: 0000000020000280 RDI: 0000000000000003 >>>>> RBP: 00007fd947ff0b76 R08: 0000000000000000 R09: 0000000000000000 >>>>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 >>>>> R13: 0000000000000000 R14: 00007fd948135f80 R15: 00007ffc6cab9d78 >>>>> </TASK> >>>>> >>>>> Allocated by task 8716: >>>>> kasan_save_stack+0x33/0x60 mm/kasan/common.c:47 >>>>> kasan_save_track+0x14/0x30 mm/kasan/common.c:68 >>>>> poison_kmalloc_redzone mm/kasan/common.c:370 [inline] >>>>> __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:387 >>>>> kasan_kmalloc include/linux/kasan.h:211 [inline] >>>>> __do_kmalloc_node mm/slub.c:4159 [inline] >>>>> __kmalloc_node_track_caller_noprof+0x20f/0x440 mm/slub.c:4178 >>>>> kmalloc_reserve+0xef/0x2c0 net/core/skbuff.c:609 >>>>> __alloc_skb+0x164/0x380 net/core/skbuff.c:678 >>>>> alloc_skb include/linux/skbuff.h:1322 [inline] >>>>> nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:748 [inline] >>>>> nsim_dev_trap_report drivers/net/netdevsim/dev.c:805 [inline] >>>>> nsim_dev_trap_report_work+0x2a4/0xc80 drivers/net/netdevsim/dev.c:850 >>>>> process_one_work+0x958/0x1ad0 kernel/workqueue.c:3231 >>>>> process_scheduled_works kernel/workqueue.c:3312 [inline] >>>>> worker_thread+0x6c8/0xf00 kernel/workqueue.c:3393 >>>>> kthread+0x2c1/0x3a0 kernel/kthread.c:389 >>>>> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147 >>>>> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 >>>>> >>>>> Freed by task 8716: >>>>> kasan_save_stack+0x33/0x60 mm/kasan/common.c:47 >>>>> kasan_save_track+0x14/0x30 mm/kasan/common.c:68 >>>>> kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:579 >>>>> poison_slab_object+0xf7/0x160 mm/kasan/common.c:240 >>>>> __kasan_slab_free+0x32/0x50 mm/kasan/common.c:256 >>>>> kasan_slab_free include/linux/kasan.h:184 [inline] >>>>> slab_free_hook mm/slub.c:2250 [inline] >>>>> slab_free mm/slub.c:4474 [inline] >>>>> kfree+0x12a/0x3b0 mm/slub.c:4595 >>>>> skb_kfree_head net/core/skbuff.c:1086 [inline] >>>>> skb_free_head+0x108/0x1d0 net/core/skbuff.c:1098 >>>>> skb_release_data+0x75d/0x990 net/core/skbuff.c:1125 >>>>> skb_release_all net/core/skbuff.c:1190 [inline] >>>>> __kfree_skb net/core/skbuff.c:1204 [inline] >>>>> consume_skb net/core/skbuff.c:1436 [inline] >>>>> consume_skb+0xbf/0x100 net/core/skbuff.c:1430 >>>>> nsim_dev_trap_report drivers/net/netdevsim/dev.c:821 [inline] >>>>> nsim_dev_trap_report_work+0x878/0xc80 drivers/net/netdevsim/dev.c:850 >>>>> process_one_work+0x958/0x1ad0 kernel/workqueue.c:3231 >>>>> process_scheduled_works kernel/workqueue.c:3312 [inline] >>>>> worker_thread+0x6c8/0xf00 kernel/workqueue.c:3393 >>>>> kthread+0x2c1/0x3a0 kernel/kthread.c:389 >>>>> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147 >>>>> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 >>>>> >>>>> The buggy address belongs to the object at ffff8880773fa000 >>>>> which belongs to the cache kmalloc-4k of size 4096 >>>>> The buggy address is located 16 bytes inside of >>>>> freed 4096-byte region [ffff8880773fa000, ffff8880773fb000) >>>>> >>>>> The buggy address belongs to the physical page: >>>>> page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x773f8 >>>>> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 >>>>> flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff) >>>>> page_type: 0xfdffffff(slab) >>>>> raw: 00fff00000000040 ffff88801ac42140 ffffea0001e63600 dead000000000002 >>>>> raw: 0000000000000000 0000000000040004 00000001fdffffff 0000000000000000 >>>>> head: 00fff00000000040 ffff88801ac42140 ffffea0001e63600 dead000000000002 >>>>> head: 0000000000000000 0000000000040004 00000001fdffffff 0000000000000000 >>>>> head: 00fff00000000003 ffffea0001dcfe01 ffffffffffffffff 0000000000000000 >>>>> head: 0000000700000008 0000000000000000 00000000ffffffff 0000000000000000 >>>>> page dumped because: kasan: bad access detected >>>>> page_owner tracks the page as allocated >>>>> page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5240, tgid 5240 (syz-executor), ts 74499202771, free_ts 74134964798 >>>>> set_page_owner include/linux/page_owner.h:32 [inline] >>>>> post_alloc_hook+0x2d1/0x350 mm/page_alloc.c:1500 >>>>> prep_new_page mm/page_alloc.c:1508 [inline] >>>>> get_page_from_freelist+0x1351/0x2e50 mm/page_alloc.c:3446 >>>>> __alloc_pages_noprof+0x22b/0x2460 mm/page_alloc.c:4702 >>>>> __alloc_pages_node_noprof include/linux/gfp.h:269 [inline] >>>>> alloc_pages_node_noprof include/linux/gfp.h:296 [inline] >>>>> alloc_slab_page+0x4e/0xf0 mm/slub.c:2319 >>>>> allocate_slab mm/slub.c:2482 [inline] >>>>> new_slab+0x84/0x260 mm/slub.c:2535 >>>>> ___slab_alloc+0xdac/0x1870 mm/slub.c:3721 >>>>> __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3811 >>>>> __slab_alloc_node mm/slub.c:3864 [inline] >>>>> slab_alloc_node mm/slub.c:4026 [inline] >>>>> __do_kmalloc_node mm/slub.c:4158 [inline] >>>>> __kmalloc_noprof+0x379/0x410 mm/slub.c:4171 >>>>> kmalloc_noprof include/linux/slab.h:694 [inline] >>>>> tomoyo_realpath_from_path+0xbf/0x710 security/tomoyo/realpath.c:251 >>>>> tomoyo_get_realpath security/tomoyo/file.c:151 [inline] >>>>> tomoyo_path_number_perm+0x245/0x5b0 security/tomoyo/file.c:723 >>>>> security_file_ioctl+0x9b/0x240 security/security.c:2908 >>>>> __do_sys_ioctl fs/ioctl.c:901 [inline] >>>>> __se_sys_ioctl fs/ioctl.c:893 [inline] >>>>> __x64_sys_ioctl+0xbb/0x210 fs/ioctl.c:893 >>>>> do_syscall_x64 arch/x86/entry/common.c:52 [inline] >>>>> do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83 >>>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f >>>>> page last free pid 5233 tgid 5233 stack trace: >>>>> reset_page_owner include/linux/page_owner.h:25 [inline] >>>>> free_pages_prepare mm/page_alloc.c:1101 [inline] >>>>> free_unref_folios+0x9e9/0x1390 mm/page_alloc.c:2667 >>>>> folios_put_refs+0x560/0x760 mm/swap.c:1039 >>>>> free_pages_and_swap_cache+0x36d/0x510 mm/swap_state.c:332 >>>>> __tlb_batch_free_encoded_pages+0xf9/0x290 mm/mmu_gather.c:136 >>>>> tlb_batch_pages_flush mm/mmu_gather.c:149 [inline] >>>>> tlb_flush_mmu_free mm/mmu_gather.c:366 [inline] >>>>> tlb_flush_mmu mm/mmu_gather.c:373 [inline] >>>>> tlb_finish_mmu+0x168/0x7b0 mm/mmu_gather.c:465 >>>>> unmap_region+0x342/0x420 mm/mmap.c:2441 >>>>> do_vmi_align_munmap+0x1107/0x19c0 mm/mmap.c:2754 >>>>> do_vmi_munmap+0x231/0x410 mm/mmap.c:2830 >>>>> __vm_munmap+0x142/0x330 mm/mmap.c:3109 >>>>> __do_sys_munmap mm/mmap.c:3126 [inline] >>>>> __se_sys_munmap mm/mmap.c:3123 [inline] >>>>> __x64_sys_munmap+0x61/0x90 mm/mmap.c:3123 >>>>> do_syscall_x64 arch/x86/entry/common.c:52 [inline] >>>>> do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83 >>>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f >>>>> >>>>> Memory state around the buggy address: >>>>> ffff8880773f9f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >>>>> ffff8880773f9f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >>>>>> ffff8880773fa000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>> ^ >>>>> ffff8880773fa080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>> ffff8880773fa100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>> ================================================================== >>>>> >>>>> >>>>> --- >>>>> 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. >>>>> >>>>> If the report is already addressed, let syzbot know by replying with: >>>>> #syz fix: exact-commit-title >>>>> >>>>> If you want to overwrite report's subsystems, reply with: >>>>> #syz set subsystems: new-subsystem >>>>> (See the list of subsystem names on the web dashboard) >>>>> >>>>> If the report is a duplicate of another one, reply with: >>>>> #syz dup: exact-subject-of-another-report >>>>> >>>>> If you want to undo deduplication, reply with: >>>>> #syz undup >>>> >>>> So we're tearing down the server and cleaning out the nfsd_file hash, >>>> and we hit a UAF. That probably means that we freed a nfsd_file without >>>> removing it from the hash? Maybe we should add a WARN_ON() in >>>> nfsd_file_slab_free that checks whether the item is still hashed? >>>> >>>> It is strange though. struct nfsd_file is 112 bytes on my machine, but >>>> the warning is about a 4k allocation. I guess that just means that the >>>> page got recycled into a different slabcache. >>> >>> The code that is crashing hasn't come close to touching anything that is >>> thought to be an nfsd_file. >>> The error is detected in the list_add() in rhashtable_walk_enter() when >>> the new on-stack iterator is being attached to the bucket_table that is being >>> iterated. So that bucket_table must (now) be an invalid address. >>> >>> The handling of NFSD_FILE_CACHE_UP is strange. nfsd_file_cache_init() >>> sets it, but doesn't clear it on failure. So if nfsd_file_cache_init() >>> fails for some reason, nfsd_file_cache_shutdown() would still try to >>> clean up if it was called. >>> >>> So suppose nfsd_startup_generic() is called. It increments nfsd_users >>> from 0 so continues to nfsd_file_cache_init() which fails for some >>> reason after initialising nfsd_file_rhltable and then destroying it. >>> This will leave nfsd_file_rhltable.tbl as a pointer to a large >>> allocation which has been freed. nfsd_startup_generic() will then >>> decrement nfsd_users back to zero, but NFSD_FILE_CACHE_UP will still be >>> set. >>> >>> When nfsd_startup_generic() is called again, nfsd_file_cache_init() will >>> skip initialisation because NFSD_FILE_CACHE_UP is set. When >>> nfsd_file_cache_shutdown() is then called it will clean up an rhltable >>> that has already been destroyed. We get exactly the reported symptom. >>> >>> I *think* nfsd_file_cache_init() can only fail with -ENOMEM and I would >>> expect to see a warning when that happened. In any case >>> nfsd_file_cache_init() uses pr_err() for any failure except >>> rhltable_init(), and that only fails if the params are inconsistent. >>> >>> So I think there are problems with NFSD_FILE_CACHE_UP settings and I >>> think they could trigger this bug if a kmalloc failed, but I don't think >>> that a kmalloc failed and I think there must be some other explanation >>> here. >> >> Also, the FILE_CACHE_UP logic has been around for several releases. >> Why is this UAF showing up only now? The "unable to register" >> messages suggest a possible reason. >> > > Good point. I didn't notice those. 111 is ECONNREFUSED, so it sounds > like rpcbind isn't up in this situation. Maybe that's a hint toward a > reproducer? I've enabled KASAN, shut down NFSD, and disabled rpcbind. Using the /proc/fs/nfsd/threads interface, I can reproduce the "unable to register" messages, but not the KASAN splat. I think Neil's analysis above is correct or very close. I don't have nfsdctl set up here, but my guess is that the syzbot is abusing the new netlink command API, causing nfsd_file_cache_init() to fail somehow and the error flow is leaving the kernel vulnerable to a UAF. -- Chuck Lever
