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

From: Eric Biggers <[email-masked]>
Date: Wed, 31 Jan 2018 13:06:09 -0800

On Sat, Dec 09, 2017 at 02:40:00AM -0800, syzbot wrote:
> 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
> ==================================================================
> 
> 
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to [email-masked].
> Please credit me with: Reported-by: syzbot <[email-masked]>
> 
> syzbot will keep track of this bug report.
> Once a fix for this bug is merged into any tree, reply to this email with:
> #syz fix: exact-commit-title

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