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Subject[PATCH 3.16 65/87] neigh: fix use-after-free read in pneigh_get_next
3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

commit f3e92cb8e2eb8c27d109e6fd73d3a69a8c09e288 upstream.

Nine years ago, I added RCU handling to neighbours, not pneighbours.
(pneigh are not commonly used)

Unfortunately I missed that /proc dump operations would use a
common entry and exit point : neigh_seq_start() and neigh_seq_stop()

We need to read_lock(tbl->lock) or risk use-after-free while
iterating the pneigh structures.

We might later convert pneigh to RCU and revert this patch.

sysbot reported :

BUG: KASAN: use-after-free in pneigh_get_next.isra.0+0x24b/0x280 net/core/neighbour.c:3158
Read of size 8 at addr ffff888097f2a700 by task syz-executor.0/9825

CPU: 1 PID: 9825 Comm: syz-executor.0 Not tainted 5.2.0-rc4+ #32
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
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
pneigh_get_next.isra.0+0x24b/0x280 net/core/neighbour.c:3158
neigh_seq_next+0xdb/0x210 net/core/neighbour.c:3240
seq_read+0x9cf/0x1110 fs/seq_file.c:258
proc_reg_read+0x1fc/0x2c0 fs/proc/inode.c:221
do_loop_readv_writev fs/read_write.c:714 [inline]
do_loop_readv_writev fs/read_write.c:701 [inline]
do_iter_read+0x4a4/0x660 fs/read_write.c:935
vfs_readv+0xf0/0x160 fs/read_write.c:997
kernel_readv fs/splice.c:359 [inline]
default_file_splice_read+0x475/0x890 fs/splice.c:414
do_splice_to+0x127/0x180 fs/splice.c:877
splice_direct_to_actor+0x2d2/0x970 fs/splice.c:954
do_splice_direct+0x1da/0x2a0 fs/splice.c:1063
do_sendfile+0x597/0xd00 fs/read_write.c:1464
__do_sys_sendfile64 fs/read_write.c:1525 [inline]
__se_sys_sendfile64 fs/read_write.c:1511 [inline]
__x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1511
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4592c9
Code: fd b7 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 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f4aab51dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00000000004592c9
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000005
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000080000000 R11: 0000000000000246 R12: 00007f4aab51e6d4
R13: 00000000004c689d R14: 00000000004db828 R15: 00000000ffffffff

Allocated by task 9827:
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 mm/slab.c:3660 [inline]
__kmalloc+0x15c/0x740 mm/slab.c:3669
kmalloc include/linux/slab.h:552 [inline]
pneigh_lookup+0x19c/0x4a0 net/core/neighbour.c:731
arp_req_set_public net/ipv4/arp.c:1010 [inline]
arp_req_set+0x613/0x720 net/ipv4/arp.c:1026
arp_ioctl+0x652/0x7f0 net/ipv4/arp.c:1226
inet_ioctl+0x2a0/0x340 net/ipv4/af_inet.c:926
sock_do_ioctl+0xd8/0x2f0 net/socket.c:1043
sock_ioctl+0x3ed/0x780 net/socket.c:1194
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9824:
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
pneigh_ifdown_and_unlock net/core/neighbour.c:812 [inline]
__neigh_ifdown+0x236/0x2f0 net/core/neighbour.c:356
neigh_ifdown+0x20/0x30 net/core/neighbour.c:372
arp_ifdown+0x1d/0x21 net/ipv4/arp.c:1274
inetdev_destroy net/ipv4/devinet.c:319 [inline]
inetdev_event+0xa14/0x11f0 net/ipv4/devinet.c:1544
notifier_call_chain+0xc2/0x230 kernel/notifier.c:95
__raw_notifier_call_chain kernel/notifier.c:396 [inline]
raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:403
call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1749
call_netdevice_notifiers_extack net/core/dev.c:1761 [inline]
call_netdevice_notifiers net/core/dev.c:1775 [inline]
rollback_registered_many+0x9b9/0xfc0 net/core/dev.c:8178
rollback_registered+0x109/0x1d0 net/core/dev.c:8220
unregister_netdevice_queue net/core/dev.c:9267 [inline]
unregister_netdevice_queue+0x1ee/0x2c0 net/core/dev.c:9260
unregister_netdevice include/linux/netdevice.h:2631 [inline]
__tun_detach+0xd8a/0x1040 drivers/net/tun.c:724
tun_detach drivers/net/tun.c:741 [inline]
tun_chr_close+0xe0/0x180 drivers/net/tun.c:3451
__fput+0x2ff/0x890 fs/file_table.c:280
____fput+0x16/0x20 fs/file_table.c:313
task_work_run+0x145/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:185 [inline]
exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:168
prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
do_syscall_64+0x58e/0x680 arch/x86/entry/common.c:304
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff888097f2a700
which belongs to the cache kmalloc-64 of size 64
The buggy address is located 0 bytes inside of
64-byte region [ffff888097f2a700, ffff888097f2a740)
The buggy address belongs to the page:
page:ffffea00025fca80 refcount:1 mapcount:0 mapping:ffff8880aa400340 index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea000250d548 ffffea00025726c8 ffff8880aa400340
raw: 0000000000000000 ffff888097f2a000 0000000100000020 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888097f2a600: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
ffff888097f2a680: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff888097f2a700: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
^
ffff888097f2a780: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff888097f2a800: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc

Fixes: 767e97e1e0db ("neigh: RCU conversion of struct neighbour")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/core/neighbour.c | 7 +++++++
1 file changed, 7 insertions(+)

--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2649,6 +2649,7 @@ static void *neigh_get_idx_any(struct se
}

void *neigh_seq_start(struct seq_file *seq, loff_t *pos, struct neigh_table *tbl, unsigned int neigh_seq_flags)
+ __acquires(tbl->lock)
__acquires(rcu_bh)
{
struct neigh_seq_state *state = seq->private;
@@ -2659,6 +2660,7 @@ void *neigh_seq_start(struct seq_file *s

rcu_read_lock_bh();
state->nht = rcu_dereference_bh(tbl->nht);
+ read_lock(&tbl->lock);

return *pos ? neigh_get_idx_any(seq, pos) : SEQ_START_TOKEN;
}
@@ -2692,8 +2694,13 @@ out:
EXPORT_SYMBOL(neigh_seq_next);

void neigh_seq_stop(struct seq_file *seq, void *v)
+ __releases(tbl->lock)
__releases(rcu_bh)
{
+ struct neigh_seq_state *state = seq->private;
+ struct neigh_table *tbl = state->tbl;
+
+ read_unlock(&tbl->lock);
rcu_read_unlock_bh();
}
EXPORT_SYMBOL(neigh_seq_stop);
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