From 345daff2e994ee844d6a609c37f085695fbb4c4d Mon Sep 17 00:00:00 2001 From: Alexey Gladkov Date: Tue, 27 Jul 2021 17:24:18 +0200 Subject: ucounts: Fix race condition between alloc_ucounts and put_ucounts The race happens because put_ucounts() doesn't use spinlock and get_ucounts is not under spinlock: CPU0 CPU1 ---- ---- alloc_ucounts() put_ucounts() spin_lock_irq(&ucounts_lock); ucounts = find_ucounts(ns, uid, hashent); atomic_dec_and_test(&ucounts->count)) spin_unlock_irq(&ucounts_lock); spin_lock_irqsave(&ucounts_lock, flags); hlist_del_init(&ucounts->node); spin_unlock_irqrestore(&ucounts_lock, flags); kfree(ucounts); ucounts = get_ucounts(ucounts); ================================================================== BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:101 [inline] BUG: KASAN: use-after-free in atomic_add_negative include/asm-generic/atomic-instrumented.h:556 [inline] BUG: KASAN: use-after-free in get_ucounts kernel/ucount.c:152 [inline] BUG: KASAN: use-after-free in get_ucounts kernel/ucount.c:150 [inline] BUG: KASAN: use-after-free in alloc_ucounts+0x19b/0x5b0 kernel/ucount.c:188 Write of size 4 at addr ffff88802821e41c by task syz-executor.4/16785 CPU: 1 PID: 16785 Comm: syz-executor.4 Not tainted 5.14.0-rc1-next-20210712-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105 print_address_description.constprop.0.cold+0x6c/0x309 mm/kasan/report.c:233 __kasan_report mm/kasan/report.c:419 [inline] kasan_report.cold+0x83/0xdf mm/kasan/report.c:436 check_region_inline mm/kasan/generic.c:183 [inline] kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189 instrument_atomic_read_write include/linux/instrumented.h:101 [inline] atomic_add_negative include/asm-generic/atomic-instrumented.h:556 [inline] get_ucounts kernel/ucount.c:152 [inline] get_ucounts kernel/ucount.c:150 [inline] alloc_ucounts+0x19b/0x5b0 kernel/ucount.c:188 set_cred_ucounts+0x171/0x3a0 kernel/cred.c:684 __sys_setuid+0x285/0x400 kernel/sys.c:623 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+0x44/0xae RIP: 0033:0x4665d9 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 bc ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fde54097188 EFLAGS: 00000246 ORIG_RAX: 0000000000000069 RAX: ffffffffffffffda RBX: 000000000056bf80 RCX: 00000000004665d9 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000000000ff RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf80 R13: 00007ffc8655740f R14: 00007fde54097300 R15: 0000000000022000 Allocated by task 16784: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 kasan_set_track mm/kasan/common.c:46 [inline] set_alloc_info mm/kasan/common.c:434 [inline] ____kasan_kmalloc mm/kasan/common.c:513 [inline] ____kasan_kmalloc mm/kasan/common.c:472 [inline] __kasan_kmalloc+0x9b/0xd0 mm/kasan/common.c:522 kmalloc include/linux/slab.h:591 [inline] kzalloc include/linux/slab.h:721 [inline] alloc_ucounts+0x23d/0x5b0 kernel/ucount.c:169 set_cred_ucounts+0x171/0x3a0 kernel/cred.c:684 __sys_setuid+0x285/0x400 kernel/sys.c:623 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+0x44/0xae Freed by task 16785: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 kasan_set_track+0x1c/0x30 mm/kasan/common.c:46 kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:360 ____kasan_slab_free mm/kasan/common.c:366 [inline] ____kasan_slab_free mm/kasan/common.c:328 [inline] __kasan_slab_free+0xfb/0x130 mm/kasan/common.c:374 kasan_slab_free include/linux/kasan.h:229 [inline] slab_free_hook mm/slub.c:1650 [inline] slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1675 slab_free mm/slub.c:3235 [inline] kfree+0xeb/0x650 mm/slub.c:4295 put_ucounts kernel/ucount.c:200 [inline] put_ucounts+0x117/0x150 kernel/ucount.c:192 put_cred_rcu+0x27a/0x520 kernel/cred.c:124 rcu_do_batch kernel/rcu/tree.c:2550 [inline] rcu_core+0x7ab/0x1380 kernel/rcu/tree.c:2785 __do_softirq+0x29b/0x9c2 kernel/softirq.c:558 Last potentially related work creation: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:348 insert_work+0x48/0x370 kernel/workqueue.c:1332 __queue_work+0x5c1/0xed0 kernel/workqueue.c:1498 queue_work_on+0xee/0x110 kernel/workqueue.c:1525 queue_work include/linux/workqueue.h:507 [inline] call_usermodehelper_exec+0x1f0/0x4c0 kernel/umh.c:435 kobject_uevent_env+0xf8f/0x1650 lib/kobject_uevent.c:618 netdev_queue_add_kobject net/core/net-sysfs.c:1621 [inline] netdev_queue_update_kobjects+0x374/0x450 net/core/net-sysfs.c:1655 register_queue_kobjects net/core/net-sysfs.c:1716 [inline] netdev_register_kobject+0x35a/0x430 net/core/net-sysfs.c:1959 register_netdevice+0xd33/0x1500 net/core/dev.c:10331 nsim_init_netdevsim drivers/net/netdevsim/netdev.c:317 [inline] nsim_create+0x381/0x4d0 drivers/net/netdevsim/netdev.c:364 __nsim_dev_port_add+0x32e/0x830 drivers/net/netdevsim/dev.c:1295 nsim_dev_port_add_all+0x53/0x150 drivers/net/netdevsim/dev.c:1355 nsim_dev_probe+0xcb5/0x1190 drivers/net/netdevsim/dev.c:1496 call_driver_probe drivers/base/dd.c:517 [inline] really_probe+0x23c/0xcd0 drivers/base/dd.c:595 __driver_probe_device+0x338/0x4d0 drivers/base/dd.c:747 driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:777 __device_attach_driver+0x20b/0x2f0 drivers/base/dd.c:894 bus_for_each_drv+0x15f/0x1e0 drivers/base/bus.c:427 __device_attach+0x228/0x4a0 drivers/base/dd.c:965 bus_probe_device+0x1e4/0x290 drivers/base/bus.c:487 device_add+0xc2f/0x2180 drivers/base/core.c:3356 nsim_bus_dev_new drivers/net/netdevsim/bus.c:431 [inline] new_device_store+0x436/0x710 drivers/net/netdevsim/bus.c:298 bus_attr_store+0x72/0xa0 drivers/base/bus.c:122 sysfs_kf_write+0x110/0x160 fs/sysfs/file.c:139 kernfs_fop_write_iter+0x342/0x500 fs/kernfs/file.c:296 call_write_iter include/linux/fs.h:2152 [inline] new_sync_write+0x426/0x650 fs/read_write.c:518 vfs_write+0x75a/0xa40 fs/read_write.c:605 ksys_write+0x12d/0x250 fs/read_write.c:658 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+0x44/0xae Second to last potentially related work creation: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38 kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:348 insert_work+0x48/0x370 kernel/workqueue.c:1332 __queue_work+0x5c1/0xed0 kernel/workqueue.c:1498 queue_work_on+0xee/0x110 kernel/workqueue.c:1525 queue_work include/linux/workqueue.h:507 [inline] call_usermodehelper_exec+0x1f0/0x4c0 kernel/umh.c:435 kobject_uevent_env+0xf8f/0x1650 lib/kobject_uevent.c:618 kobject_synth_uevent+0x701/0x850 lib/kobject_uevent.c:208 uevent_store+0x20/0x50 drivers/base/core.c:2371 dev_attr_store+0x50/0x80 drivers/base/core.c:2072 sysfs_kf_write+0x110/0x160 fs/sysfs/file.c:139 kernfs_fop_write_iter+0x342/0x500 fs/kernfs/file.c:296 call_write_iter include/linux/fs.h:2152 [inline] new_sync_write+0x426/0x650 fs/read_write.c:518 vfs_write+0x75a/0xa40 fs/read_write.c:605 ksys_write+0x12d/0x250 fs/read_write.c:658 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+0x44/0xae The buggy address belongs to the object at ffff88802821e400 which belongs to the cache kmalloc-192 of size 192 The buggy address is located 28 bytes inside of 192-byte region [ffff88802821e400, ffff88802821e4c0) The buggy address belongs to the page: page:ffffea0000a08780 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2821e flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff) raw: 00fff00000000200 dead000000000100 dead000000000122 ffff888010841a00 raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected page_owner tracks the page as allocated page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 1, ts 12874702440, free_ts 12637793385 prep_new_page mm/page_alloc.c:2433 [inline] get_page_from_freelist+0xa72/0x2f80 mm/page_alloc.c:4166 __alloc_pages+0x1b2/0x500 mm/page_alloc.c:5374 alloc_page_interleave+0x1e/0x200 mm/mempolicy.c:2119 alloc_pages+0x238/0x2a0 mm/mempolicy.c:2242 alloc_slab_page mm/slub.c:1713 [inline] allocate_slab+0x32b/0x4c0 mm/slub.c:1853 new_slab mm/slub.c:1916 [inline] new_slab_objects mm/slub.c:2662 [inline] ___slab_alloc+0x4ba/0x820 mm/slub.c:2825 __slab_alloc.constprop.0+0xa7/0xf0 mm/slub.c:2865 slab_alloc_node mm/slub.c:2947 [inline] slab_alloc mm/slub.c:2989 [inline] __kmalloc+0x312/0x330 mm/slub.c:4133 kmalloc include/linux/slab.h:596 [inline] kzalloc include/linux/slab.h:721 [inline] __register_sysctl_table+0x112/0x1090 fs/proc/proc_sysctl.c:1318 rds_tcp_init_net+0x1db/0x4f0 net/rds/tcp.c:551 ops_init+0xaf/0x470 net/core/net_namespace.c:140 __register_pernet_operations net/core/net_namespace.c:1137 [inline] register_pernet_operations+0x35a/0x850 net/core/net_namespace.c:1214 register_pernet_device+0x26/0x70 net/core/net_namespace.c:1301 rds_tcp_init+0x77/0xe0 net/rds/tcp.c:717 do_one_initcall+0x103/0x650 init/main.c:1285 do_initcall_level init/main.c:1360 [inline] do_initcalls init/main.c:1376 [inline] do_basic_setup init/main.c:1396 [inline] kernel_init_freeable+0x6b8/0x741 init/main.c:1598 page last free stack trace: reset_page_owner include/linux/page_owner.h:24 [inline] free_pages_prepare mm/page_alloc.c:1343 [inline] free_pcp_prepare+0x312/0x7d0 mm/page_alloc.c:1394 free_unref_page_prepare mm/page_alloc.c:3329 [inline] free_unref_page+0x19/0x690 mm/page_alloc.c:3408 __vunmap+0x783/0xb70 mm/vmalloc.c:2587 free_work+0x58/0x70 mm/vmalloc.c:82 process_one_work+0x98d/0x1630 kernel/workqueue.c:2276 worker_thread+0x658/0x11f0 kernel/workqueue.c:2422 kthread+0x3e5/0x4d0 kernel/kthread.c:319 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 Memory state around the buggy address: ffff88802821e300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff88802821e380: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc >ffff88802821e400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88802821e480: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff88802821e500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ================================================================== - The race fix has two parts. * Changing the code to guarantee that ucounts->count is only decremented when ucounts_lock is held. This guarantees that find_ucounts will never find a structure with a zero reference count. * Changing alloc_ucounts to increment ucounts->count while ucounts_lock is held. This guarantees the reference count on the found data structure will not be decremented to zero (and the data structure freed) before the reference count is incremented. -- Eric Biederman Reported-by: syzbot+01985d7909f9468f013c@syzkaller.appspotmail.com Reported-by: syzbot+59dd63761094a80ad06d@syzkaller.appspotmail.com Reported-by: syzbot+6cd79f45bb8fa1c9eeae@syzkaller.appspotmail.com Reported-by: syzbot+b6e65bd125a05f803d6b@syzkaller.appspotmail.com Fixes: b6c336528926 ("Use atomic_t for ucounts reference counting") Cc: Hillf Danton Signed-off-by: Alexey Gladkov Link: https://lkml.kernel.org/r/7b2ace1759b281cdd2d66101d6b305deef722efb.1627397820.git.legion@kernel.org Signed-off-by: Eric W. Biederman --- kernel/ucount.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) (limited to 'kernel/ucount.c') diff --git a/kernel/ucount.c b/kernel/ucount.c index 87799e2379bd..77be3bbe3cc4 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -160,6 +160,7 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) { struct hlist_head *hashent = ucounts_hashentry(ns, uid); struct ucounts *ucounts, *new; + long overflow; spin_lock_irq(&ucounts_lock); ucounts = find_ucounts(ns, uid, hashent); @@ -184,8 +185,12 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) return new; } } + overflow = atomic_add_negative(1, &ucounts->count); spin_unlock_irq(&ucounts_lock); - ucounts = get_ucounts(ucounts); + if (overflow) { + put_ucounts(ucounts); + return NULL; + } return ucounts; } @@ -193,8 +198,7 @@ void put_ucounts(struct ucounts *ucounts) { unsigned long flags; - if (atomic_dec_and_test(&ucounts->count)) { - spin_lock_irqsave(&ucounts_lock, flags); + if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) { hlist_del_init(&ucounts->node); spin_unlock_irqrestore(&ucounts_lock, flags); kfree(ucounts); -- cgit v1.2.3