KASAN: slab-out-of-bounds Read in sctp_send_reset_streams

[syzbot]

Hello,

syzkaller hit the following crash on
328b4ed93b69a6f2083d52f31a240a09e5de386a
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


==================================================================
BUG: KASAN: slab-out-of-bounds in sctp_send_reset_streams+0xadf/0xc10
net/sctp/stream.c:314
Read of size 2 at addr ffff8801d8a6c048 by task syzkaller104411/3085

CPU: 0 PID: 3085 Comm: syzkaller104411 Not tainted 4.15.0-rc2+ #119
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x257 lib/dump_stack.c:53
print_address_description+0x73/0x250 mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report+0x25b/0x340 mm/kasan/report.c:409
__asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:428
sctp_send_reset_streams+0xadf/0xc10 net/sctp/stream.c:314
sctp_setsockopt_reset_streams net/sctp/socket.c:3905 [inline]
sctp_setsockopt+0x70d/0x5d50 net/sctp/socket.c:4195
compat_sock_common_setsockopt+0x104/0x140 net/core/sock.c:2981
C_SYSC_setsockopt net/compat.c:403 [inline]
compat_SyS_setsockopt+0x17c/0x410 net/compat.c:386
do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:125
RIP: 0023:0xf7f1bc79
RSP: 002b:00000000ff9893bc EFLAGS: 00000282 ORIG_RAX: 000000000000016e
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000000084
RDX: 0000000000000077 RSI: 000000002018b000 RDI: 0000000000000008
RBP: 000000000000001c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 3085:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
__do_kmalloc mm/slab.c:3711 [inline]
__kmalloc_track_caller+0x15e/0x760 mm/slab.c:3726
memdup_user+0x2c/0x90 mm/util.c:164
sctp_setsockopt_reset_streams net/sctp/socket.c:3897 [inline]
sctp_setsockopt+0x6a6/0x5d50 net/sctp/socket.c:4195
compat_sock_common_setsockopt+0x104/0x140 net/core/sock.c:2981
C_SYSC_setsockopt net/compat.c:403 [inline]
compat_SyS_setsockopt+0x17c/0x410 net/compat.c:386
do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:125

Freed by task 16:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3491 [inline]
kfree+0xca/0x250 mm/slab.c:3806
selinux_cred_free+0x48/0x70 security/selinux/hooks.c:3814
security_cred_free+0x48/0x80 security/security.c:995
put_cred_rcu+0x106/0x400 kernel/cred.c:117
__rcu_reclaim kernel/rcu/rcu.h:195 [inline]
rcu_do_batch kernel/rcu/tree.c:2758 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:3012 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2979 [inline]
rcu_process_callbacks+0xd74/0x17d0 kernel/rcu/tree.c:2996
__do_softirq+0x29d/0xbb2 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801d8a6c040
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 8 bytes inside of
32-byte region [ffff8801d8a6c040, ffff8801d8a6c060)
The buggy address belongs to the page:
page:000000006b05592a count:1 mapcount:0 mapping:000000001ca7267d
index:0xffff8801d8a6cfc1
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801d8a6c000 ffff8801d8a6cfc1 000000010000003f
raw: ffffea000762f920 ffffea00076133e0 ffff8801db0001c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d8a6bf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801d8a6bf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801d8a6c000: fb fb fb fb fc fc fc fc 00 fc fc fc fc fc fc fc
^
ffff8801d8a6c080: fb fb fb fb fc fc fc fc 00 00 00 00 fc fc fc fc
ffff8801d8a6c100: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
==================================================================


---
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[Xin Long]

On Sat, Dec 9, 2017 at 6:40 PM, syzbot
<bot+0665d43fa62276c7a5...@syzkaller.appspotmail.com>
wrote:

the check:
if (optlen < sizeof(struct sctp_reset_streams))
in sctp_setsockopt_reset_streams() is not correct, the srs_stream_list
memory should have been counted as well.

[Xin Long]

Fix:

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index ac6338f..1532a49 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3930,6 +3930,10 @@ static int sctp_setsockopt_reset_streams(struct sock *sk,
if (IS_ERR(params))
return PTR_ERR(params);

+ if (params->srs_number_streams * sizeof(__u16) >
+ optlen - sizeof(*params))
+ goto out;
+

[Eric Biggers]

This crash is no longer occurring. I assume it was fixed by commit
2342b8d95bcae5 (thanks Xin!), so let's tell syzbot:

#syz fix: sctp: make sure stream nums can match optlen in sctp_setsockopt_reset_streams

- Eric