3c8fc87820
syszbot found an interesting use-after-free [1] happening while IPv4 fragment rhashtable was destroyed at netns dismantle. While no insertions can possibly happen at the time a dismantling netns is destroying this rhashtable, timers can still fire and attempt to remove elements from this rhashtable. This is forbidden, since rhashtable_free_and_destroy() has no synchronization against concurrent inserts and deletes. Add a new fqdir->dead flag so that timers do not attempt a rhashtable_remove_fast() operation. We also have to respect an RCU grace period before starting the rhashtable_free_and_destroy() from process context, thus we use rcu_work infrastructure. This is a refinement of a prior rough attempt to fix this bug : https://marc.info/?l=linux-netdev&m=153845936820900&w=2 Since the rhashtable cleanup is now deferred to a work queue, netns dismantles should be slightly faster. [1] BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:194 [inline] BUG: KASAN: use-after-free in rhashtable_last_table+0x162/0x180 lib/rhashtable.c:212 Read of size 8 at addr ffff8880a6497b70 by task kworker/0:0/5 CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.2.0-rc1+ #2 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: events rht_deferred_worker Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x172/0x1f0 lib/dump_stack.c:113 print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188 __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317 kasan_report+0x12/0x20 mm/kasan/common.c:614 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132 __read_once_size include/linux/compiler.h:194 [inline] rhashtable_last_table+0x162/0x180 lib/rhashtable.c:212 rht_deferred_worker+0x111/0x2030 lib/rhashtable.c:411 process_one_work+0x989/0x1790 kernel/workqueue.c:2269 worker_thread+0x98/0xe40 kernel/workqueue.c:2415 kthread+0x354/0x420 kernel/kthread.c:255 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 Allocated by task 32687: save_stack+0x23/0x90 mm/kasan/common.c:71 set_track mm/kasan/common.c:79 [inline] __kasan_kmalloc mm/kasan/common.c:489 [inline] __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503 __do_kmalloc_node mm/slab.c:3620 [inline] __kmalloc_node+0x4e/0x70 mm/slab.c:3627 kmalloc_node include/linux/slab.h:590 [inline] kvmalloc_node+0x68/0x100 mm/util.c:431 kvmalloc include/linux/mm.h:637 [inline] kvzalloc include/linux/mm.h:645 [inline] bucket_table_alloc+0x90/0x480 lib/rhashtable.c:178 rhashtable_init+0x3f4/0x7b0 lib/rhashtable.c:1057 inet_frags_init_net include/net/inet_frag.h:109 [inline] ipv4_frags_init_net+0x182/0x410 net/ipv4/ip_fragment.c:683 ops_init+0xb3/0x410 net/core/net_namespace.c:130 setup_net+0x2d3/0x740 net/core/net_namespace.c:316 copy_net_ns+0x1df/0x340 net/core/net_namespace.c:439 create_new_namespaces+0x400/0x7b0 kernel/nsproxy.c:107 unshare_nsproxy_namespaces+0xc2/0x200 kernel/nsproxy.c:206 ksys_unshare+0x440/0x980 kernel/fork.c:2692 __do_sys_unshare kernel/fork.c:2760 [inline] __se_sys_unshare kernel/fork.c:2758 [inline] __x64_sys_unshare+0x31/0x40 kernel/fork.c:2758 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301 entry_SYSCALL_64_after_hwframe+0x49/0xbe Freed by task 7: save_stack+0x23/0x90 mm/kasan/common.c:71 set_track mm/kasan/common.c:79 [inline] __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451 kasan_slab_free+0xe/0x10 mm/kasan/common.c:459 __cache_free mm/slab.c:3432 [inline] kfree+0xcf/0x220 mm/slab.c:3755 kvfree+0x61/0x70 mm/util.c:460 bucket_table_free+0x69/0x150 lib/rhashtable.c:108 rhashtable_free_and_destroy+0x165/0x8b0 lib/rhashtable.c:1155 inet_frags_exit_net+0x3d/0x50 net/ipv4/inet_fragment.c:152 ipv4_frags_exit_net+0x73/0x90 net/ipv4/ip_fragment.c:695 ops_exit_list.isra.0+0xaa/0x150 net/core/net_namespace.c:154 cleanup_net+0x3fb/0x960 net/core/net_namespace.c:553 process_one_work+0x989/0x1790 kernel/workqueue.c:2269 worker_thread+0x98/0xe40 kernel/workqueue.c:2415 kthread+0x354/0x420 kernel/kthread.c:255 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 The buggy address belongs to the object at ffff8880a6497b40 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 48 bytes inside of 1024-byte region [ffff8880a6497b40, ffff8880a6497f40) The buggy address belongs to the page: page:ffffea0002992580 refcount:1 mapcount:0 mapping:ffff8880aa400ac0 index:0xffff8880a64964c0 compound_mapcount: 0 flags: 0x1fffc0000010200(slab|head) raw: 01fffc0000010200 ffffea0002916e88 ffffea000218fe08 ffff8880aa400ac0 raw: ffff8880a64964c0 ffff8880a6496040 0000000100000005 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8880a6497a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880a6497a80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc >ffff8880a6497b00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb ^ ffff8880a6497b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880a6497c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb Fixes: 648700f76b03 ("inet: frags: use rhashtables for reassembly units") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
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