KASAN: use-after-free Read in rtnetlink_put_metrics

KASAN: use-after-free Read in rtnetlink_put_metrics

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    61f4b23769f0 netlink: Don't shift with UB on nlk->ngroups
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=14a9de58400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ffb4428fdc82f93b
dashboard link: https://syzkaller.appspot.com/bug?extid=41f9c04b50ef70c66947
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+41f9c04b50ef70c66947@syzkaller.appspotmail.com

TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending  
cookies.  Check SNMP counters.
==================================================================
BUG: KASAN: use-after-free in rtnetlink_put_metrics+0x621/0x690  
net/core/rtnetlink.c:754
Read of size 4 at addr ffff8801b3cd8b00 by task udevd/2613

CPU: 0 PID: 2613 Comm: udevd Not tainted 4.18.0-rc6+ #34
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  <IRQ>
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
  print_address_description+0x6c/0x20b mm/kasan/report.c:256
  kasan_report_error mm/kasan/report.c:354 [inline]
  kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
  __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
  rtnetlink_put_metrics+0x621/0x690 net/core/rtnetlink.c:754
  rt6_fill_node+0x7d9/0x1540 net/ipv6/route.c:4753
  inet6_rt_notify+0x161/0x2c0 net/ipv6/route.c:4985
  fib6_del_route net/ipv6/ip6_fib.c:1788 [inline]
  fib6_del+0xf4d/0x1310 net/ipv6/ip6_fib.c:1815
  fib6_clean_node+0x3ee/0x5e0 net/ipv6/ip6_fib.c:1976
  fib6_walk_continue+0x4b1/0x8e0 net/ipv6/ip6_fib.c:1899
  fib6_walk+0x95/0xf0 net/ipv6/ip6_fib.c:1947
  fib6_clean_tree+0x1ea/0x360 net/ipv6/ip6_fib.c:2024
  __fib6_clean_all+0x21c/0x420 net/ipv6/ip6_fib.c:2040
  fib6_clean_all net/ipv6/ip6_fib.c:2051 [inline]
  fib6_run_gc+0x182/0x3d0 net/ipv6/ip6_fib.c:2107
  fib6_gc_timer_cb+0x20/0x30 net/ipv6/ip6_fib.c:2124
  call_timer_fn+0x242/0x970 kernel/time/timer.c:1326
  expire_timers kernel/time/timer.c:1363 [inline]
  __run_timers+0x7a6/0xc70 kernel/time/timer.c:1666
  run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
  __do_softirq+0x2e8/0xb17 kernel/softirq.c:292
  invoke_softirq kernel/softirq.c:372 [inline]
  irq_exit+0x1d4/0x210 kernel/softirq.c:412
  exiting_irq arch/x86/include/asm/apic.h:527 [inline]
  smp_apic_timer_interrupt+0x186/0x730 arch/x86/kernel/apic/apic.c:1052
  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
  </IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:783  
[inline]
RIP: 0010:qlink_free mm/kasan/quarantine.c:150 [inline]
RIP: 0010:qlist_free_all+0xf8/0x160 mm/kasan/quarantine.c:166
Code: c7 40 10 00 00 00 00 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8  
57 b8 a4 ff 48 83 3d 67 b4 37 06 00 74 56 48 89 df 57 9d <0f> 1f 44 00 00  
eb af ba 00 00 00 80 48 01 c2 72 43 48 b9 00 00 00
RSP: 0018:ffff8801b54a7b08 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000007 RBX: 0000000000000286 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff8801b5498a38 RDI: 0000000000000286
RBP: ffff8801b54a7b40 R08: ffff8801b5498a38 R09: 0000000000000006
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff8801dad85dc0 R14: ffff8801b37ace00 R15: ffffffff87f1b0a0
  quarantine_reduce+0x163/0x1a0 mm/kasan/quarantine.c:259
  kasan_kmalloc+0x99/0xe0 mm/kasan/kasan.c:538
  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
  slab_post_alloc_hook mm/slab.h:444 [inline]
  slab_alloc mm/slab.c:3392 [inline]
  kmem_cache_alloc+0x11b/0x760 mm/slab.c:3552
  getname_flags+0xd0/0x5a0 fs/namei.c:140
  user_path_at_empty+0x2d/0x50 fs/namei.c:2584
  do_readlinkat+0x14b/0x400 fs/stat.c:394
  __do_sys_readlink fs/stat.c:427 [inline]
  __se_sys_readlink fs/stat.c:424 [inline]
  __x64_sys_readlink+0x78/0xb0 fs/stat.c:424
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7efd8271b577
Code: f0 ff ff 77 02 f3 c3 48 8b 15 bd 38 2b 00 f7 d8 64 89 02 83 c8 ff c3  
90 90 90 90 90 90 90 90 90 90 90 90 b8 59 00 00 00 0f 05 <48> 3d 01 f0 ff  
ff 73 01 c3 48 8b 0d 91 38 2b 00 31 d2 48 29 c2 64
RSP: 002b:00007ffe27d23688 EFLAGS: 00000246 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00000000021de250 RCX: 00007efd8271b577
RDX: 0000000000000400 RSI: 00007ffe27d23690 RDI: 00007ffe27d23b70
RBP: 00007ffe27d243b0 R08: 00007ffe27d243b0 R09: 00007efd8276fdc0
R10: 7665642f7379732f R11: 0000000000000246 R12: 00007ffe27d23b70
R13: 0000000000000400 R14: 00000000021de250 R15: 00000000021e3e10

Allocated by task 8953:
  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
  set_track mm/kasan/kasan.c:460 [inline]
  kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
  kmem_cache_alloc_trace+0x152/0x780 mm/slab.c:3620
  kmalloc include/linux/slab.h:513 [inline]
  kzalloc include/linux/slab.h:707 [inline]
  fib6_metric_set+0x163/0x2c0 net/ipv6/ip6_fib.c:645
  fib6_add_rt2node+0xe36/0x27f0 net/ipv6/ip6_fib.c:1000
  fib6_add+0xaae/0x14d0 net/ipv6/ip6_fib.c:1308
  __ip6_ins_rt+0x54/0x80 net/ipv6/route.c:1163
  ip6_route_add+0x6d/0xc0 net/ipv6/route.c:3171
  addrconf_prefix_route.isra.48+0x51d/0x720 net/ipv6/addrconf.c:2347
  inet6_addr_modify net/ipv6/addrconf.c:4627 [inline]
  inet6_rtm_newaddr+0x112e/0x1b50 net/ipv6/addrconf.c:4743
  rtnetlink_rcv_msg+0x46e/0xc30 net/core/rtnetlink.c:4665
  netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2453
  rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4683
  netlink_unicast_kernel net/netlink/af_netlink.c:1315 [inline]
  netlink_unicast+0x5a0/0x760 net/netlink/af_netlink.c:1341
  netlink_sendmsg+0xa18/0xfd0 net/netlink/af_netlink.c:1906
  sock_sendmsg_nosec net/socket.c:642 [inline]
  sock_sendmsg+0xd5/0x120 net/socket.c:652
  ___sys_sendmsg+0x7fd/0x930 net/socket.c:2126
  __sys_sendmsg+0x11d/0x290 net/socket.c:2164
  __do_sys_sendmsg net/socket.c:2173 [inline]
  __se_sys_sendmsg net/socket.c:2171 [inline]
  __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2171
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 2613:
  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
  set_track mm/kasan/kasan.c:460 [inline]
  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
  __cache_free mm/slab.c:3498 [inline]
  kfree+0xd9/0x260 mm/slab.c:3813
  fib6_metrics_release+0x77/0x90 net/ipv6/ip6_fib.c:179
  fib6_drop_pcpu_from net/ipv6/ip6_fib.c:899 [inline]
  fib6_purge_rt+0x5ec/0x7f0 net/ipv6/ip6_fib.c:934
  fib6_del_route net/ipv6/ip6_fib.c:1784 [inline]
  fib6_del+0xc11/0x1310 net/ipv6/ip6_fib.c:1815
  fib6_clean_node+0x3ee/0x5e0 net/ipv6/ip6_fib.c:1976
  fib6_walk_continue+0x4b1/0x8e0 net/ipv6/ip6_fib.c:1899
  fib6_walk+0x95/0xf0 net/ipv6/ip6_fib.c:1947
  fib6_clean_tree+0x1ea/0x360 net/ipv6/ip6_fib.c:2024
  __fib6_clean_all+0x21c/0x420 net/ipv6/ip6_fib.c:2040
  fib6_clean_all net/ipv6/ip6_fib.c:2051 [inline]
  fib6_run_gc+0x182/0x3d0 net/ipv6/ip6_fib.c:2107
  fib6_gc_timer_cb+0x20/0x30 net/ipv6/ip6_fib.c:2124
  call_timer_fn+0x242/0x970 kernel/time/timer.c:1326
  expire_timers kernel/time/timer.c:1363 [inline]
  __run_timers+0x7a6/0xc70 kernel/time/timer.c:1666
  run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
  __do_softirq+0x2e8/0xb17 kernel/softirq.c:292

The buggy address belongs to the object at ffff8801b3cd8b00
  which belongs to the cache kmalloc-96 of size 96
The buggy address is located 0 bytes inside of
  96-byte region [ffff8801b3cd8b00, ffff8801b3cd8b60)
The buggy address belongs to the page:
page:ffffea0006cf3600 count:1 mapcount:0 mapping:ffff8801dac004c0 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0006a6f3c8 ffffea0007018608 ffff8801dac004c0
raw: 0000000000000000 ffff8801b3cd8000 0000000100000020 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801b3cd8a00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
  ffff8801b3cd8a80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
> ffff8801b3cd8b00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                    ^
  ffff8801b3cd8b80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
  ffff8801b3cd8c00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
==================================================================


---
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Re: KASAN: use-after-free Read in rtnetlink_put_metrics

[Eric Dumazet]

On 07/31/2018 05:31 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    61f4b23769f0 netlink: Don't shift with UB on nlk->ngroups
> git tree:       net
> console output: https://syzkaller.appspot.com/x/log.txt?x=14a9de58400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ffb4428fdc82f93b
> dashboard link: https://syzkaller.appspot.com/bug?extid=41f9c04b50ef70c66947
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+41f9c04b50ef70c66947@syzkaller.appspotmail.com
> 
> TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending cookies.  Check SNMP counters.
> ==================================================================
> BUG: KASAN: use-after-free in rtnetlink_put_metrics+0x621/0x690 net/core/rtnetlink.c:754
> Read of size 4 at addr ffff8801b3cd8b00 by task udevd/2613
> 
> CPU: 0 PID: 2613 Comm: udevd Not tainted 4.18.0-rc6+ #34
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  <IRQ>
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
>  __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
>  rtnetlink_put_metrics+0x621/0x690 net/core/rtnetlink.c:754
>  rt6_fill_node+0x7d9/0x1540 net/ipv6/route.c:4753
>  inet6_rt_notify+0x161/0x2c0 net/ipv6/route.c:4985
>  fib6_del_route net/ipv6/ip6_fib.c:1788 [inline]
>  fib6_del+0xf4d/0x1310 net/ipv6/ip6_fib.c:1815
>  fib6_clean_node+0x3ee/0x5e0 net/ipv6/ip6_fib.c:1976
>  fib6_walk_continue+0x4b1/0x8e0 net/ipv6/ip6_fib.c:1899
>  fib6_walk+0x95/0xf0 net/ipv6/ip6_fib.c:1947
>  fib6_clean_tree+0x1ea/0x360 net/ipv6/ip6_fib.c:2024
>  __fib6_clean_all+0x21c/0x420 net/ipv6/ip6_fib.c:2040
>  fib6_clean_all net/ipv6/ip6_fib.c:2051 [inline]
>  fib6_run_gc+0x182/0x3d0 net/ipv6/ip6_fib.c:2107
>  fib6_gc_timer_cb+0x20/0x30 net/ipv6/ip6_fib.c:2124
>  call_timer_fn+0x242/0x970 kernel/time/timer.c:1326
>  expire_timers kernel/time/timer.c:1363 [inline]
>  __run_timers+0x7a6/0xc70 kernel/time/timer.c:1666
>  run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
>  __do_softirq+0x2e8/0xb17 kernel/softirq.c:292
>  invoke_softirq kernel/softirq.c:372 [inline]
>  irq_exit+0x1d4/0x210 kernel/softirq.c:412
>  exiting_irq arch/x86/include/asm/apic.h:527 [inline]
>  smp_apic_timer_interrupt+0x186/0x730 arch/x86/kernel/apic/apic.c:1052
>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
>  </IRQ>
> RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:783 [inline]
> RIP: 0010:qlink_free mm/kasan/quarantine.c:150 [inline]
> RIP: 0010:qlist_free_all+0xf8/0x160 mm/kasan/quarantine.c:166
> Code: c7 40 10 00 00 00 00 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 57 b8 a4 ff 48 83 3d 67 b4 37 06 00 74 56 48 89 df 57 9d <0f> 1f 44 00 00 eb af ba 00 00 00 80 48 01 c2 72 43 48 b9 00 00 00
> RSP: 0018:ffff8801b54a7b08 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
> RAX: 0000000000000007 RBX: 0000000000000286 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffff8801b5498a38 RDI: 0000000000000286
> RBP: ffff8801b54a7b40 R08: ffff8801b5498a38 R09: 0000000000000006
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: ffff8801dad85dc0 R14: ffff8801b37ace00 R15: ffffffff87f1b0a0
>  quarantine_reduce+0x163/0x1a0 mm/kasan/quarantine.c:259
>  kasan_kmalloc+0x99/0xe0 mm/kasan/kasan.c:538
>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
>  slab_post_alloc_hook mm/slab.h:444 [inline]
>  slab_alloc mm/slab.c:3392 [inline]
>  kmem_cache_alloc+0x11b/0x760 mm/slab.c:3552
>  getname_flags+0xd0/0x5a0 fs/namei.c:140
>  user_path_at_empty+0x2d/0x50 fs/namei.c:2584
>  do_readlinkat+0x14b/0x400 fs/stat.c:394
>  __do_sys_readlink fs/stat.c:427 [inline]
>  __se_sys_readlink fs/stat.c:424 [inline]
>  __x64_sys_readlink+0x78/0xb0 fs/stat.c:424
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x7efd8271b577
> Code: f0 ff ff 77 02 f3 c3 48 8b 15 bd 38 2b 00 f7 d8 64 89 02 83 c8 ff c3 90 90 90 90 90 90 90 90 90 90 90 90 b8 59 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 91 38 2b 00 31 d2 48 29 c2 64
> RSP: 002b:00007ffe27d23688 EFLAGS: 00000246 ORIG_RAX: 0000000000000059
> RAX: ffffffffffffffda RBX: 00000000021de250 RCX: 00007efd8271b577
> RDX: 0000000000000400 RSI: 00007ffe27d23690 RDI: 00007ffe27d23b70
> RBP: 00007ffe27d243b0 R08: 00007ffe27d243b0 R09: 00007efd8276fdc0
> R10: 7665642f7379732f R11: 0000000000000246 R12: 00007ffe27d23b70
> R13: 0000000000000400 R14: 00000000021de250 R15: 00000000021e3e10
> 
> Allocated by task 8953:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
>  kmem_cache_alloc_trace+0x152/0x780 mm/slab.c:3620
>  kmalloc include/linux/slab.h:513 [inline]
>  kzalloc include/linux/slab.h:707 [inline]
>  fib6_metric_set+0x163/0x2c0 net/ipv6/ip6_fib.c:645
>  fib6_add_rt2node+0xe36/0x27f0 net/ipv6/ip6_fib.c:1000
>  fib6_add+0xaae/0x14d0 net/ipv6/ip6_fib.c:1308
>  __ip6_ins_rt+0x54/0x80 net/ipv6/route.c:1163
>  ip6_route_add+0x6d/0xc0 net/ipv6/route.c:3171
>  addrconf_prefix_route.isra.48+0x51d/0x720 net/ipv6/addrconf.c:2347
>  inet6_addr_modify net/ipv6/addrconf.c:4627 [inline]
>  inet6_rtm_newaddr+0x112e/0x1b50 net/ipv6/addrconf.c:4743
>  rtnetlink_rcv_msg+0x46e/0xc30 net/core/rtnetlink.c:4665
>  netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2453
>  rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4683
>  netlink_unicast_kernel net/netlink/af_netlink.c:1315 [inline]
>  netlink_unicast+0x5a0/0x760 net/netlink/af_netlink.c:1341
>  netlink_sendmsg+0xa18/0xfd0 net/netlink/af_netlink.c:1906
>  sock_sendmsg_nosec net/socket.c:642 [inline]
>  sock_sendmsg+0xd5/0x120 net/socket.c:652
>  ___sys_sendmsg+0x7fd/0x930 net/socket.c:2126
>  __sys_sendmsg+0x11d/0x290 net/socket.c:2164
>  __do_sys_sendmsg net/socket.c:2173 [inline]
>  __se_sys_sendmsg net/socket.c:2171 [inline]
>  __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2171
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 2613:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>  __cache_free mm/slab.c:3498 [inline]
>  kfree+0xd9/0x260 mm/slab.c:3813
>  fib6_metrics_release+0x77/0x90 net/ipv6/ip6_fib.c:179
>  fib6_drop_pcpu_from net/ipv6/ip6_fib.c:899 [inline]
>  fib6_purge_rt+0x5ec/0x7f0 net/ipv6/ip6_fib.c:934
>  fib6_del_route net/ipv6/ip6_fib.c:1784 [inline]
>  fib6_del+0xc11/0x1310 net/ipv6/ip6_fib.c:1815
>  fib6_clean_node+0x3ee/0x5e0 net/ipv6/ip6_fib.c:1976
>  fib6_walk_continue+0x4b1/0x8e0 net/ipv6/ip6_fib.c:1899
>  fib6_walk+0x95/0xf0 net/ipv6/ip6_fib.c:1947
>  fib6_clean_tree+0x1ea/0x360 net/ipv6/ip6_fib.c:2024
>  __fib6_clean_all+0x21c/0x420 net/ipv6/ip6_fib.c:2040
>  fib6_clean_all net/ipv6/ip6_fib.c:2051 [inline]
>  fib6_run_gc+0x182/0x3d0 net/ipv6/ip6_fib.c:2107
>  fib6_gc_timer_cb+0x20/0x30 net/ipv6/ip6_fib.c:2124
>  call_timer_fn+0x242/0x970 kernel/time/timer.c:1326
>  expire_timers kernel/time/timer.c:1363 [inline]
>  __run_timers+0x7a6/0xc70 kernel/time/timer.c:1666
>  run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
>  __do_softirq+0x2e8/0xb17 kernel/softirq.c:292
> 
> The buggy address belongs to the object at ffff8801b3cd8b00
>  which belongs to the cache kmalloc-96 of size 96
> The buggy address is located 0 bytes inside of
>  96-byte region [ffff8801b3cd8b00, ffff8801b3cd8b60)
> The buggy address belongs to the page:
> page:ffffea0006cf3600 count:1 mapcount:0 mapping:ffff8801dac004c0 index:0x0
> flags: 0x2fffc0000000100(slab)
> raw: 02fffc0000000100 ffffea0006a6f3c8 ffffea0007018608 ffff8801dac004c0
> raw: 0000000000000000 ffff8801b3cd8000 0000000100000020 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8801b3cd8a00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>  ffff8801b3cd8a80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>> ffff8801b3cd8b00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>                    ^
>  ffff8801b3cd8b80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>  ffff8801b3cd8c00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
> ==================================================================
> 
> 
> ---
> This bug 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@googlegroups.com.
> 
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with syzbot.

Probably also caused by :


commit df18b50448fab1dff093731dfd0e25e77e1afcd1
Author: Sabrina Dubroca <sd@queasysnail.net>
Date:   Mon Jul 30 16:23:10 2018 +0200

    net/ipv6: fix metrics leak

Re: KASAN: use-after-free Read in rtnetlink_put_metrics

[Sabrina Dubroca]

2018-07-31, 05:41:56 -0700, Eric Dumazet wrote:
> 
> 
> On 07/31/2018 05:31 AM, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following crash on:
> > 
> > HEAD commit:    61f4b23769f0 netlink: Don't shift with UB on nlk->ngroups
> > git tree:       net
> > console output: https://syzkaller.appspot.com/x/log.txt?x=14a9de58400000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=ffb4428fdc82f93b
> > dashboard link: https://syzkaller.appspot.com/bug?extid=41f9c04b50ef70c66947
> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > 
> > Unfortunately, I don't have any reproducer for this crash yet.
[...]

> Probably also caused by :
> 
> 
> commit df18b50448fab1dff093731dfd0e25e77e1afcd1
> Author: Sabrina Dubroca <sd@queasysnail.net>
> Date:   Mon Jul 30 16:23:10 2018 +0200
> 
>     net/ipv6: fix metrics leak

Yeah, I'm looking into both those reports :/

-- 
Sabrina

Re: KASAN: use-after-free Read in rtnetlink_put_metrics

[David Miller]

From: Sabrina Dubroca <sd@queasysnail.net>
Date: Tue, 31 Jul 2018 15:40:14 +0200

> 2018-07-31, 05:41:56 -0700, Eric Dumazet wrote:
>> Probably also caused by :
>> 
>> 
>> commit df18b50448fab1dff093731dfd0e25e77e1afcd1
>> Author: Sabrina Dubroca <sd@queasysnail.net>
>> Date:   Mon Jul 30 16:23:10 2018 +0200
>> 
>>     net/ipv6: fix metrics leak
> 
> Yeah, I'm looking into both those reports :/

Please get me a fix for this soon, because as you can imagine this is
going to hold up the 4.18 release.

Thanks.

Re: KASAN: use-after-free Read in rtnetlink_put_metrics

[Cong Wang]

On Tue, Jul 31, 2018 at 6:41 AM Sabrina Dubroca <sd@queasysnail.net> wrote:
>
> 2018-07-31, 05:41:56 -0700, Eric Dumazet wrote:
> >
> >
> > On 07/31/2018 05:31 AM, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following crash on:
> > >
> > > HEAD commit:    61f4b23769f0 netlink: Don't shift with UB on nlk->ngroups
> > > git tree:       net
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=14a9de58400000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=ffb4428fdc82f93b
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=41f9c04b50ef70c66947
> > > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > >
> > > Unfortunately, I don't have any reproducer for this crash yet.
> [...]
>
> > Probably also caused by :
> >
> >
> > commit df18b50448fab1dff093731dfd0e25e77e1afcd1
> > Author: Sabrina Dubroca <sd@queasysnail.net>
> > Date:   Mon Jul 30 16:23:10 2018 +0200
> >
> >     net/ipv6: fix metrics leak
>
> Yeah, I'm looking into both those reports :/

Looks like this commit is completely unnecessary,
fib6_drop_pcpu_from() calls fib6_info_release()
which calls fib6_info_destroy_rcu(), so this metrics
will be released twice...

Re: KASAN: use-after-free Read in rtnetlink_put_metrics

[Sabrina Dubroca]

2018-07-31, 16:03:13 -0700, Cong Wang wrote:
> On Tue, Jul 31, 2018 at 6:41 AM Sabrina Dubroca <sd@queasysnail.net> wrote:
> >
> > 2018-07-31, 05:41:56 -0700, Eric Dumazet wrote:
> > >
> > >
> > > On 07/31/2018 05:31 AM, syzbot wrote:
> > > > Hello,
> > > >
> > > > syzbot found the following crash on:
> > > >
> > > > HEAD commit:    61f4b23769f0 netlink: Don't shift with UB on nlk->ngroups
> > > > git tree:       net
> > > > console output: https://syzkaller.appspot.com/x/log.txt?x=14a9de58400000
> > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=ffb4428fdc82f93b
> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=41f9c04b50ef70c66947
> > > > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > > >
> > > > Unfortunately, I don't have any reproducer for this crash yet.
> > [...]
> >
> > > Probably also caused by :
> > >
> > >
> > > commit df18b50448fab1dff093731dfd0e25e77e1afcd1
> > > Author: Sabrina Dubroca <sd@queasysnail.net>
> > > Date:   Mon Jul 30 16:23:10 2018 +0200
> > >
> > >     net/ipv6: fix metrics leak
> >
> > Yeah, I'm looking into both those reports :/
> 
> Looks like this commit is completely unnecessary,
> fib6_drop_pcpu_from() calls fib6_info_release()
> which calls fib6_info_destroy_rcu(), so this metrics
> will be released twice...

kmemleak disagrees:

unreferenced object 0xffff88006b605080 (size 96):
  comm "ip", pid 433, jiffies 4294889793 (age 74.844s)
  hex dump (first 32 bytes):
    00 00 00 00 f4 01 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<000000002650e4e2>] ip6_route_info_create+0x770/0x4050
    [<000000000a8d4c52>] ip6_route_add+0x18/0x90
    [<00000000474d669c>] inet6_rtm_newroute+0xeb/0x100
    [<0000000019fb732d>] rtnetlink_rcv_msg+0x3b5/0xb40
    [<000000006f891e19>] netlink_rcv_skb+0x137/0x380
    [<0000000070451985>] netlink_unicast+0x47f/0x6e0
    [<000000004487d656>] netlink_sendmsg+0x7a7/0x10c0
    [<0000000089fdf5ae>] sock_sendmsg+0xac/0x160
    [<00000000aae19c54>] ___sys_sendmsg+0x6e0/0xbb0
    [<00000000a3906352>] __sys_sendmsg+0xdc/0x230
    [<00000000c7c8548a>] do_syscall_64+0x15d/0x740
    [<000000007dfdad73>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
    [<000000003adb705a>] 0xffffffffffffffff


ip netns add peerA
ip link add eth0 netns peerA type veth peer name ethA
ip -net peerA link set eth0 up
ip -net peerA link set lo up
ip -net peerA a a fec0:A::1/64 dev eth0
ip -net peerA route add fec0:B::/64 via fec0:A:: mtu 1300

ip netns exec peerA nc fec0:B::1 1234

ip -net peerA route del fec0:B::/64
ip netns del peerA

-- 
Sabrina

Re: KASAN: use-after-free Read in rtnetlink_put_metrics

[David Ahern]

On 8/1/18 10:15 AM, Sabrina Dubroca wrote:
> ip -net peerA route add fec0:B::/64 via fec0:A:: mtu 1300

I am on vacation right now with limited access to internet, so not able
to take a look.

In submitting the fib6_info changes I did tests like this and did not
see memleak reports (and verified the metrics refcnts with printks), so
I am surprised to see your patch in this area. Will take a look when I
can but that will not be for a couple more weeks.

Re: KASAN: use-after-free Read in rtnetlink_put_metrics

[David Miller]

From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Tue, 31 Jul 2018 16:03:13 -0700

> Looks like this commit is completely unnecessary,
> fib6_drop_pcpu_from() calls fib6_info_release()
> which calls fib6_info_destroy_rcu(), so this metrics
> will be released twice...

And even if there was a leak here, it's illegal to free this
metrics memory synchronously since it is RCU protected.

That's why it normally goes through fib6_info_destroy_rcu().

Sabrina, I'm going to revert your changes unless I see some
progress here by the end of today.

Re: KASAN: use-after-free Read in rtnetlink_put_metrics

[Sabrina Dubroca]

2018-08-01, 11:46:36 -0700, David Miller wrote:
> From: Cong Wang <xiyou.wangcong@gmail.com>
> Date: Tue, 31 Jul 2018 16:03:13 -0700
> 
> > Looks like this commit is completely unnecessary,
> > fib6_drop_pcpu_from() calls fib6_info_release()
> > which calls fib6_info_destroy_rcu(), so this metrics
> > will be released twice...
> 
> And even if there was a leak here, it's illegal to free this
> metrics memory synchronously since it is RCU protected.

Yeah, I noticed that today, but I don't think that's the problem we're
seeing here.

> That's why it normally goes through fib6_info_destroy_rcu().
> 
> Sabrina, I'm going to revert your changes unless I see some
> progress here by the end of today.

Yeah, I'm fine with a revert, we can fix the leak later.


syzbot hasn't found a reproducer so I'm not sure it's the same issue,
but I ran into this: we can create a route, start using it, and then
give it some metrics. In that case, we'll hit rt6_set_from() with the
default metrics, so we don't refcount them. Then fib6_metric_set()
will assign the new metrics to the parent route.
Then fib6_drop_pcpu_from will see that the parent route has
non-default metrics, and try to release this, but the percpu copy
doesn't actually hold a reference. Bandaid would be to put a
DST_METRICS_REFCOUNTED check in fib6_drop_pcpu_from().

Looking at rt6_set_from(), it seems we can also do dst_init_metrics
with the old metrics, then refcount the new metrics.

And I'm not sure whether the refcount_set in fib6_metric_set() can't
be reordered so that rt6_set_from() might see the new metrics pointer,
increment the refcount, then fib6_metric_set() would do its
refcount_set, stepping over the previous increment.

-- 
Sabrina

Re: KASAN: use-after-free Read in rtnetlink_put_metrics

[Cong Wang]

On Wed, Aug 1, 2018 at 1:15 AM Sabrina Dubroca <sd@queasysnail.net> wrote:
>
> 2018-07-31, 16:03:13 -0700, Cong Wang wrote:
> > On Tue, Jul 31, 2018 at 6:41 AM Sabrina Dubroca <sd@queasysnail.net> wrote:
> > >
> > > 2018-07-31, 05:41:56 -0700, Eric Dumazet wrote:
> > > >
> > > >
> > > > On 07/31/2018 05:31 AM, syzbot wrote:
> > > > > Hello,
> > > > >
> > > > > syzbot found the following crash on:
> > > > >
> > > > > HEAD commit:    61f4b23769f0 netlink: Don't shift with UB on nlk->ngroups
> > > > > git tree:       net
> > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=14a9de58400000
> > > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=ffb4428fdc82f93b
> > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=41f9c04b50ef70c66947
> > > > > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > > > >
> > > > > Unfortunately, I don't have any reproducer for this crash yet.
> > > [...]
> > >
> > > > Probably also caused by :
> > > >
> > > >
> > > > commit df18b50448fab1dff093731dfd0e25e77e1afcd1
> > > > Author: Sabrina Dubroca <sd@queasysnail.net>
> > > > Date:   Mon Jul 30 16:23:10 2018 +0200
> > > >
> > > >     net/ipv6: fix metrics leak
> > >
> > > Yeah, I'm looking into both those reports :/
> >
> > Looks like this commit is completely unnecessary,
> > fib6_drop_pcpu_from() calls fib6_info_release()
> > which calls fib6_info_destroy_rcu(), so this metrics
> > will be released twice...
>
> kmemleak disagrees:


This information is missing from changelog. :)


>
> unreferenced object 0xffff88006b605080 (size 96):
>   comm "ip", pid 433, jiffies 4294889793 (age 74.844s)
>   hex dump (first 32 bytes):
>     00 00 00 00 f4 01 00 00 00 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<000000002650e4e2>] ip6_route_info_create+0x770/0x4050
>     [<000000000a8d4c52>] ip6_route_add+0x18/0x90
>     [<00000000474d669c>] inet6_rtm_newroute+0xeb/0x100
>     [<0000000019fb732d>] rtnetlink_rcv_msg+0x3b5/0xb40
>     [<000000006f891e19>] netlink_rcv_skb+0x137/0x380
>     [<0000000070451985>] netlink_unicast+0x47f/0x6e0
>     [<000000004487d656>] netlink_sendmsg+0x7a7/0x10c0
>     [<0000000089fdf5ae>] sock_sendmsg+0xac/0x160
>     [<00000000aae19c54>] ___sys_sendmsg+0x6e0/0xbb0
>     [<00000000a3906352>] __sys_sendmsg+0xdc/0x230
>     [<00000000c7c8548a>] do_syscall_64+0x15d/0x740
>     [<000000007dfdad73>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
>     [<000000003adb705a>] 0xffffffffffffffff

My kernel dev machine is broken now.
I will take a look tomorrow after I fix my kernel dev machine.

Thanks!