On Sun, Apr 28, 2019 at 12:24 PM Eric Dumazet <eduma...@google.com> wrote:
>
> We had many syzbot reports that seem to be caused by use-after-free
> of struct fib6_info.
>
> ip6_dst_destroy(), fib6_drop_pcpu_from() and rt6_remove_exception()
> are writers vs rt->from, and use non consistent synchronization among
> themselves.
>
> Switching to xchg() will solve the issues with no possible
> lockdep issues.
>
> BUG: KASAN: user-memory-access in atomic_dec_and_test
> include/asm-generic/atomic-instrumented.h:747 [inline]
> BUG: KASAN: user-memory-access in fib6_info_release include/net/ip6_fib.h:294
> [inline]
> BUG: KASAN: user-memory-access in fib6_info_release include/net/ip6_fib.h:292
> [inline]
> BUG: KASAN: user-memory-access in fib6_drop_pcpu_from net/ipv6/ip6_fib.c:927
> [inline]
> BUG: KASAN: user-memory-access in fib6_purge_rt+0x4f6/0x670
> net/ipv6/ip6_fib.c:960
> Write of size 4 at addr 0000000000ffffb4 by task syz-executor.1/7649
>
> CPU: 0 PID: 7649 Comm: syz-executor.1 Not tainted 5.1.0-rc6+ #183
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x172/0x1f0 lib/dump_stack.c:113
> kasan_report.cold+0x5/0x40 mm/kasan/report.c:321
> check_memory_region_inline mm/kasan/generic.c:185 [inline]
> check_memory_region+0x123/0x190 mm/kasan/generic.c:191
> kasan_check_write+0x14/0x20 mm/kasan/common.c:108
> atomic_dec_and_test include/asm-generic/atomic-instrumented.h:747 [inline]
> fib6_info_release include/net/ip6_fib.h:294 [inline]
> fib6_info_release include/net/ip6_fib.h:292 [inline]
> fib6_drop_pcpu_from net/ipv6/ip6_fib.c:927 [inline]
> fib6_purge_rt+0x4f6/0x670 net/ipv6/ip6_fib.c:960
> fib6_del_route net/ipv6/ip6_fib.c:1813 [inline]
> fib6_del+0xac2/0x10a0 net/ipv6/ip6_fib.c:1844
> fib6_clean_node+0x3a8/0x590 net/ipv6/ip6_fib.c:2006
> fib6_walk_continue+0x495/0x900 net/ipv6/ip6_fib.c:1928
> fib6_walk+0x9d/0x100 net/ipv6/ip6_fib.c:1976
> fib6_clean_tree+0xe0/0x120 net/ipv6/ip6_fib.c:2055
> __fib6_clean_all+0x118/0x2a0 net/ipv6/ip6_fib.c:2071
> fib6_clean_all+0x2b/0x40 net/ipv6/ip6_fib.c:2082
> rt6_sync_down_dev+0x134/0x150 net/ipv6/route.c:4057
> rt6_disable_ip+0x27/0x5f0 net/ipv6/route.c:4062
> addrconf_ifdown+0xa2/0x1220 net/ipv6/addrconf.c:3705
> addrconf_notify+0x19a/0x2260 net/ipv6/addrconf.c:3630
> notifier_call_chain+0xc7/0x240 kernel/notifier.c:93
> __raw_notifier_call_chain kernel/notifier.c:394 [inline]
> raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:401
> call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1753
> call_netdevice_notifiers_extack net/core/dev.c:1765 [inline]
> call_netdevice_notifiers net/core/dev.c:1779 [inline]
> dev_close_many+0x33f/0x6f0 net/core/dev.c:1522
> rollback_registered_many+0x43b/0xfd0 net/core/dev.c:8177
> rollback_registered+0x109/0x1d0 net/core/dev.c:8242
> unregister_netdevice_queue net/core/dev.c:9289 [inline]
> unregister_netdevice_queue+0x1ee/0x2c0 net/core/dev.c:9282
> unregister_netdevice include/linux/netdevice.h:2658 [inline]
> __tun_detach+0xd5b/0x1000 drivers/net/tun.c:727
> tun_detach drivers/net/tun.c:744 [inline]
> tun_chr_close+0xe0/0x180 drivers/net/tun.c:3443
> __fput+0x2e5/0x8d0 fs/file_table.c:278
> ____fput+0x16/0x20 fs/file_table.c:309
> task_work_run+0x14a/0x1c0 kernel/task_work.c:113
> exit_task_work include/linux/task_work.h:22 [inline]
> do_exit+0x90a/0x2fa0 kernel/exit.c:876
> do_group_exit+0x135/0x370 kernel/exit.c:980
> __do_sys_exit_group kernel/exit.c:991 [inline]
> __se_sys_exit_group kernel/exit.c:989 [inline]
> __x64_sys_exit_group+0x44/0x50 kernel/exit.c:989
> do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x458da9
> Code: ad b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f
> 83 7b b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffeafc2a6a8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 000000000000001c RCX: 0000000000458da9
> RDX: 0000000000412a80 RSI: 0000000000a54ef0 RDI: 0000000000000043
> RBP: 00000000004be552 R08: 000000000000000c R09: 000000000004c0d1
> R10: 0000000002341940 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00007ffeafc2a7f0 R14: 000000000004c065 R15: 00007ffeafc2a800
>
> Fixes: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected")
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Reported-by: syzbot <syzkal...@googlegroups.com>
> Cc: David Ahern <dsah...@gmail.com>
> ---
Acked-by: Wei Wang <wei...@google.com>
Nice fix. Thanks Eric.
> net/ipv6/ip6_fib.c | 4 +---
> net/ipv6/route.c | 9 ++-------
> 2 files changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> index
> 6613d8dbb0e5a5c3ba883c957e5bc4ba2bf00777..91247a6fc67ff7de1106d028b315a559e53e47f4
> 100644
> --- a/net/ipv6/ip6_fib.c
> +++ b/net/ipv6/ip6_fib.c
> @@ -921,9 +921,7 @@ static void fib6_drop_pcpu_from(struct fib6_info *f6i,
> if (pcpu_rt) {
> struct fib6_info *from;
>
> - from = rcu_dereference_protected(pcpu_rt->from,
> -
> lockdep_is_held(&table->tb6_lock));
> - rcu_assign_pointer(pcpu_rt->from, NULL);
> + from = xchg((__force struct fib6_info
> **)&pcpu_rt->from, NULL);
> fib6_info_release(from);
> }
> }
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index
> 7178e32eb15d0a969eb39fcfec9973bb0150bf48..19d4edf37947de33423e1d590d3e556763f9a3fb
> 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -379,11 +379,8 @@ static void ip6_dst_destroy(struct dst_entry *dst)
> in6_dev_put(idev);
> }
>
> - rcu_read_lock();
> - from = rcu_dereference(rt->from);
> - rcu_assign_pointer(rt->from, NULL);
> + from = xchg((__force struct fib6_info **)&rt->from, NULL);
> fib6_info_release(from);
> - rcu_read_unlock();
> }
>
> static void ip6_dst_ifdown(struct dst_entry *dst, struct net_device *dev,
> @@ -1288,9 +1285,7 @@ static void rt6_remove_exception(struct
> rt6_exception_bucket *bucket,
> /* purge completely the exception to allow releasing the held
> resources:
> * some [sk] cache may keep the dst around for unlimited time
> */
> - from = rcu_dereference_protected(rt6_ex->rt6i->from,
> -
> lockdep_is_held(&rt6_exception_lock));
> - rcu_assign_pointer(rt6_ex->rt6i->from, NULL);
> + from = xchg((__force struct fib6_info **)&rt6_ex->rt6i->from, NULL);
> fib6_info_release(from);
> dst_dev_put(&rt6_ex->rt6i->dst);
>
> --
> 2.21.0.593.g511ec345e18-goog
>
