KASAN: use-after-free Read in sctp_transport_get_next

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 815f0ddb346c include/linux/compiler*.h: make compiler-*.h ..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14adfea6400000
kernel config: https://syzkaller.appspot.com/x/.config?x=e408e8a7bf8306cb
dashboard link: https://syzkaller.appspot.com/bug?extid=fe62a0c9aa6a85c6de16
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=130da896400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+fe62a0...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in sctp_transport_get_next+0x11c/0x140
net/sctp/socket.c:5008
Read of size 8 at addr ffff8801d97c84e0 by task syz-executor0/12694

CPU: 1 PID: 12694 Comm: syz-executor0 Not tainted 4.18.0+ #107
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+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+0x242/0x30d mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
sctp_transport_get_next+0x11c/0x140 net/sctp/socket.c:5008
sctp_transport_get_idx net/sctp/socket.c:5022 [inline]
sctp_for_each_transport+0x152/0x370 net/sctp/socket.c:5083
sctp_diag_dump+0x3a7/0x620 net/sctp/diag.c:527
__inet_diag_dump+0xa8/0x140 net/ipv4/inet_diag.c:1049
inet_diag_dump+0x9b/0x110 net/ipv4/inet_diag.c:1065
netlink_dump+0x519/0xd50 net/netlink/af_netlink.c:2233
__netlink_dump_start+0x4f1/0x6f0 net/netlink/af_netlink.c:2329
netlink_dump_start include/linux/netlink.h:213 [inline]
inet_diag_handler_cmd+0x2ce/0x3f0 net/ipv4/inet_diag.c:1170
__sock_diag_cmd net/core/sock_diag.c:232 [inline]
sock_diag_rcv_msg+0x31d/0x410 net/core/sock_diag.c:263
netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2454
sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:274
netlink_unicast_kernel net/netlink/af_netlink.c:1317 [inline]
netlink_unicast+0x5a0/0x760 net/netlink/af_netlink.c:1343
netlink_sendmsg+0xa18/0xfc0 net/netlink/af_netlink.c:1908
sock_sendmsg_nosec net/socket.c:621 [inline]
sock_sendmsg+0xd5/0x120 net/socket.c:631
sock_write_iter+0x362/0x5c0 net/socket.c:900
call_write_iter include/linux/fs.h:1805 [inline]
do_iter_readv_writev+0x8b0/0xa80 fs/read_write.c:680
do_iter_write+0x185/0x5f0 fs/read_write.c:959
compat_writev+0x234/0x420 fs/read_write.c:1273
do_compat_writev+0x128/0x260 fs/read_write.c:1294
__do_compat_sys_writev fs/read_write.c:1305 [inline]
__se_compat_sys_writev fs/read_write.c:1301 [inline]
__ia32_compat_sys_writev+0x74/0xb0 fs/read_write.c:1301
do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
do_fast_syscall_32+0x34d/0xfb2 arch/x86/entry/common.c:397
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f6aca9
Code: 55 08 8b 88 64 cd ff ff 8b 98 68 cd ff ff 89 c8 85 d2 74 02 89 0a 5b
5d c3 8b 04 24 c3 8b 1c 24 c3 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90
90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f7f660cc EFLAGS: 00000296 ORIG_RAX: 0000000000000092
RAX: ffffffffffffffda RBX: 0000000000000009 RCX: 0000000020000000
RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 12694:
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+0x152/0x730 mm/slab.c:3620
kmalloc include/linux/slab.h:513 [inline]
kzalloc include/linux/slab.h:707 [inline]
sctp_association_new+0x127/0x2290 net/sctp/associola.c:311
sctp_unpack_cookie+0x7b4/0x1160 net/sctp/sm_make_chunk.c:1829
sctp_sf_do_5_1D_ce+0x451/0x14c0 net/sctp/sm_statefuns.c:743
sctp_do_sm+0x1c1/0x71e0 net/sctp/sm_sideeffect.c:1188
sctp_endpoint_bh_rcv+0x465/0x960 net/sctp/endpointola.c:456
sctp_inq_push+0x272/0x340 net/sctp/inqueue.c:95
sctp_rcv+0x2cb2/0x3ab0 net/sctp/input.c:268
sctp6_rcv+0x15/0x30 net/sctp/ipv6.c:1061
ip6_input_finish+0x407/0x1a40 net/ipv6/ip6_input.c:383
NF_HOOK include/linux/netfilter.h:287 [inline]
ip6_input+0xe9/0x600 net/ipv6/ip6_input.c:426
dst_input include/net/dst.h:450 [inline]
ip6_rcv_finish+0x17a/0x330 net/ipv6/ip6_input.c:76
NF_HOOK include/linux/netfilter.h:287 [inline]
ipv6_rcv+0x11e/0x650 net/ipv6/ip6_input.c:271
__netif_receive_skb_one_core+0x14d/0x200 net/core/dev.c:4892
__netif_receive_skb+0x2c/0x1e0 net/core/dev.c:5002
process_backlog+0x219/0x760 net/core/dev.c:5808
napi_poll net/core/dev.c:6228 [inline]
net_rx_action+0x799/0x1900 net/core/dev.c:6294
__do_softirq+0x2eb/0xa74 kernel/softirq.c:292

Freed by task 12693:
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+0xd9/0x210 mm/slab.c:3813
sctp_association_destroy net/sctp/associola.c:437 [inline]
sctp_association_put+0x264/0x350 net/sctp/associola.c:885
sctp_association_free+0x6c9/0x972 net/sctp/associola.c:415
sctp_cmd_delete_tcb net/sctp/sm_sideeffect.c:939 [inline]
sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1353 [inline]
sctp_side_effects net/sctp/sm_sideeffect.c:1220 [inline]
sctp_do_sm+0x4a5c/0x71e0 net/sctp/sm_sideeffect.c:1191
sctp_primitive_ABORT+0xa0/0xd0 net/sctp/primitive.c:119
sctp_close+0x279/0xa80 net/sctp/socket.c:1559
inet_release+0x104/0x1f0 net/ipv4/af_inet.c:428
inet6_release+0x50/0x70 net/ipv6/af_inet6.c:457
__sock_release+0xd7/0x250 net/socket.c:579
sock_close+0x19/0x20 net/socket.c:1139
__fput+0x36e/0x8c0 fs/file_table.c:278
____fput+0x15/0x20 fs/file_table.c:309
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_32_irqs_on arch/x86/entry/common.c:341 [inline]
do_fast_syscall_32+0xcd5/0xfb2 arch/x86/entry/common.c:397
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

The buggy address belongs to the object at ffff8801d97c84c0
which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 32 bytes inside of
4096-byte region [ffff8801d97c84c0, ffff8801d97c94c0)
The buggy address belongs to the page:
page:ffffea000765f200 count:1 mapcount:0 mapping:ffff8801dac00dc0 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffffea0007628888 ffffea0007620608 ffff8801dac00dc0
raw: 0000000000000000 ffff8801d97c84c0 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d97c8380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801d97c8400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801d97c8480: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
^
ffff8801d97c8500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d97c8580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Marcelo Ricardo Leitner]

On Fri, Aug 24, 2018 at 12:40:03AM -0700, syzbot wrote:
> CPU: 1 PID: 12694 Comm: syz-executor0 Not tainted 4.18.0+ #107
> 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+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+0x242/0x30d mm/kasan/report.c:412
> __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
> sctp_transport_get_next+0x11c/0x140 net/sctp/socket.c:5008
> sctp_transport_get_idx net/sctp/socket.c:5022 [inline]

It is iterating over transports but then also accessing the
association directly, without checking any refcnts before that.

struct sctp_transport *sctp_transport_get_next(struct net *net,
struct rhashtable_iter *iter)
{
struct sctp_transport *t;

t = rhashtable_walk_next(iter);
for (; t; t = rhashtable_walk_next(iter)) {
if (IS_ERR(t)) {
if (PTR_ERR(t) == -EAGAIN)
continue;
break;
}

if (net_eq(sock_net(t->asoc->base.sk), net) &&
t->asoc->peer.primary_path == t)
break;

and these t->asoc-> are risky because transport may be laying dead on
the water already, as transports are freed by RCU and associations are
not.

[Xin Long]

Thanks,
I will move sctp_transport_hold into sctp_transport_get_next():
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index ce620e8..4bd5c2d 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4881,9 +4881,14 @@ struct sctp_transport
*sctp_transport_get_next(struct net *net,
break;
}

+ if (!sctp_transport_hold(t))
+ continue;
+

if (net_eq(sock_net(t->asoc->base.sk), net) &&
t->asoc->peer.primary_path == t)
break;

+
+ sctp_transport_put(t);
}

return t;
@@ -4896,8 +4901,10 @@ struct sctp_transport
*sctp_transport_get_idx(struct net *net,
void *obj = SEQ_START_TOKEN;

while (pos && (obj = sctp_transport_get_next(net, iter)) &&
- !IS_ERR(obj))
+ !IS_ERR(obj)) {
pos--;
+ sctp_transport_put(obj);
+ }

return obj;
}
@@ -4958,8 +4965,6 @@ int sctp_for_each_transport(int (*cb)(struct
sctp_transport *, void *),

tsp = sctp_transport_get_idx(net, &hti, *pos + 1);
for (; !IS_ERR_OR_NULL(tsp); tsp = sctp_transport_get_next(net, &hti)) {
- if (!sctp_transport_hold(tsp))
- continue;
ret = cb(tsp, p);
if (ret)
break;

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: 2923b27e5424 Merge tag 'libnvdimm-for-4.19_dax-memory-fail..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10f01a1e400000
kernel config: https://syzkaller.appspot.com/x/.config?x=3b576e333ca31bb2

dashboard link: https://syzkaller.appspot.com/bug?extid=fe62a0c9aa6a85c6de16
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1022f96a400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13be8b32400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+fe62a0...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in sctp_transport_get_next+0x11c/0x140
net/sctp/socket.c:5008

Read of size 8 at addr ffff8801b09a23e0 by task syz-executor305/13769

CPU: 0 PID: 13769 Comm: syz-executor305 Not tainted 4.18.0+ #209

call_write_iter include/linux/fs.h:1807 [inline]

do_iter_readv_writev+0x8b0/0xa80 fs/read_write.c:680
do_iter_write+0x185/0x5f0 fs/read_write.c:959

vfs_writev+0x1f1/0x360 fs/read_write.c:1004
do_writev+0x11a/0x310 fs/read_write.c:1039
__do_sys_writev fs/read_write.c:1112 [inline]
__se_sys_writev fs/read_write.c:1109 [inline]
__x64_sys_writev+0x75/0xb0 fs/read_write.c:1109
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x446679
Code: e8 0c e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 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 0f 83 7b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f5b0050bda8 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00000000006dbc48 RCX: 0000000000446679
RDX: 0000000000000001 RSI: 0000000020000000 RDI: 0000000000000005
RBP: 00000000006dbc40 R08: 000000000000001c R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
R13: 0100000000000000 R14: 00007f5b0050c9c0 R15: 00000000006dbd4c

Allocated by task 13750:

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+0x152/0x730 mm/slab.c:3620
kmalloc include/linux/slab.h:513 [inline]
kzalloc include/linux/slab.h:707 [inline]
sctp_association_new+0x127/0x2290 net/sctp/associola.c:311

sctp_sendmsg_new_asoc+0x39e/0x1200 net/sctp/socket.c:1742
sctp_sendmsg+0x18a5/0x1da0 net/sctp/socket.c:2103
inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798

sock_sendmsg_nosec net/socket.c:621 [inline]
sock_sendmsg+0xd5/0x120 net/socket.c:631

__sys_sendto+0x3d7/0x670 net/socket.c:1786
__do_sys_sendto net/socket.c:1798 [inline]
__se_sys_sendto net/socket.c:1794 [inline]
__x64_sys_sendto+0xe1/0x1a0 net/socket.c:1794
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 13747:

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+0xd9/0x210 mm/slab.c:3813
sctp_association_destroy net/sctp/associola.c:437 [inline]
sctp_association_put+0x264/0x350 net/sctp/associola.c:885

sctp_transport_destroy net/sctp/transport.c:180 [inline]
sctp_transport_put+0x193/0x200 net/sctp/transport.c:332
sctp_backlog_rcv+0x28e/0xd50 net/sctp/input.c:357
sk_backlog_rcv include/net/sock.h:931 [inline]
__release_sock+0x12f/0x3a0 net/core/sock.c:2336
release_sock+0xad/0x2c0 net/core/sock.c:2849
sctp_close+0x49c/0xa80 net/sctp/socket.c:1569

inet_release+0x104/0x1f0 net/ipv4/af_inet.c:428
inet6_release+0x50/0x70 net/ipv6/af_inet6.c:457
__sock_release+0xd7/0x250 net/socket.c:579
sock_close+0x19/0x20 net/socket.c:1139
__fput+0x36e/0x8c0 fs/file_table.c:278
____fput+0x15/0x20 fs/file_table.c:309
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]

do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801b09a23c0

which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 32 bytes inside of

4096-byte region [ffff8801b09a23c0, ffff8801b09a33c0)

The buggy address belongs to the page:

page:ffffea0006c26880 count:1 mapcount:0 mapping:ffff8801dac00dc0 index:0x0

compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)

raw: 02fffc0000008100 ffffea0006c0f188 ffffea0006bf8108 ffff8801dac00dc0
raw: 0000000000000000 ffff8801b09a23c0 0000000100000001 0000000000000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff8801b09a2280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801b09a2300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801b09a2380: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
^
ffff8801b09a2400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801b09a2480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================