KASAN: slab-out-of-bounds Write in sctp_setsockopt

KASAN: slab-out-of-bounds Write in sctp_setsockopt

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    4f1b4da5 Merge branch 'net-atlantic-various-features'
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x\x14b3a040900000
kernel config:  https://syzkaller.appspot.com/x/.config?x+7b67c0c1819c87
dashboard link: https://syzkaller.appspot.com/bug?extid\x0e4699d000d8b874d8dc
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x\x14c93358900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x\x14ab61f0900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0e4699d000d8b874d8dc@syzkaller.appspotmail.com

sctp: [Deprecated]: syz-executor496 (pid 6834) Use of struct sctp_assoc_value in delayed_ack socket option.
Use struct sctp_sack_info instead
=================================
BUG: KASAN: slab-out-of-bounds in sctp_setsockopt_delayed_ack net/sctp/socket.c:2771 [inline]
BUG: KASAN: slab-out-of-bounds in sctp_setsockopt net/sctp/socket.c:4499 [inline]
BUG: KASAN: slab-out-of-bounds in sctp_setsockopt+0x9488/0x95e0 net/sctp/socket.c:4431
Write of size 4 at addr ffff8880a2709288 by task syz-executor496/6834

CPU: 0 PID: 6834 Comm: syz-executor496 Not tainted 5.8.0-rc4-syzkaller #0
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+0x18f/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 sctp_setsockopt_delayed_ack net/sctp/socket.c:2771 [inline]
 sctp_setsockopt net/sctp/socket.c:4499 [inline]
 sctp_setsockopt+0x9488/0x95e0 net/sctp/socket.c:4431
 __sys_setsockopt+0x337/0x6a0 net/socket.c:2137
 __do_sys_setsockopt net/socket.c:2153 [inline]
 __se_sys_setsockopt net/socket.c:2150 [inline]
 __x64_sys_setsockopt+0xba/0x150 net/socket.c:2150
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x440229
Code: Bad RIP value.
RSP: 002b:00007ffc07ceda28 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440229
RDX: 0000000000000010 RSI: 0000000000000084 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000008 R09: 00000000004002c8
R10: 0000000020000100 R11: 0000000000000246 R12: 0000000000401a30
R13: 0000000000401ac0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 6834:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
 __do_kmalloc mm/slab.c:3656 [inline]
 __kmalloc_track_caller+0x178/0x330 mm/slab.c:3671
 memdup_user+0x22/0xd0 mm/util.c:172
 sctp_setsockopt net/sctp/socket.c:4452 [inline]
 sctp_setsockopt+0x17a/0x95e0 net/sctp/socket.c:4431
 __sys_setsockopt+0x337/0x6a0 net/socket.c:2137
 __do_sys_setsockopt net/socket.c:2153 [inline]
 __se_sys_setsockopt net/socket.c:2150 [inline]
 __x64_sys_setsockopt+0xba/0x150 net/socket.c:2150
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 4827:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 kasan_set_free_info mm/kasan/common.c:316 [inline]
 __kasan_slab_free+0xf5/0x140 mm/kasan/common.c:455
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x103/0x2c0 mm/slab.c:3757
 tomoyo_path2_perm+0x28a/0x600 security/tomoyo/file.c:947
 tomoyo_path_rename+0xd2/0x130 security/tomoyo/tomoyo.c:279
 security_path_rename+0x1b5/0x2e0 security/security.c:1135
 do_renameat2+0x481/0xbf0 fs/namei.c:4446
 __do_sys_rename fs/namei.c:4496 [inline]
 __se_sys_rename fs/namei.c:4494 [inline]
 __x64_sys_rename+0x5d/0x80 fs/namei.c:4494
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff8880a2709280
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 8 bytes inside of
 32-byte region [ffff8880a2709280, ffff8880a27092a0)
The buggy address belongs to the page:
page:ffffea000289c240 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8880a2709fc1
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00026c1108 ffffea00026ae848 ffff8880aa0001c0
raw: ffff8880a2709fc1 ffff8880a2709000 000000010000003f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a2709180: 06 fc fc fc fc fc fc fc 06 fc fc fc fc fc fc fc
 ffff8880a2709200: 06 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
>ffff8880a2709280: 00 fc fc fc fc fc fc fc 05 fc fc fc fc fc fc fc
                      ^
 ffff8880a2709300: fb fb fb fb fc fc fc fc 06 fc fc fc fc fc fc fc
 ffff8880a2709380: 06 fc fc fc fc fc fc fc 06 fc fc fc fc fc fc fc
=================================


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Re: KASAN: slab-out-of-bounds Write in sctp_setsockopt

[Marcelo Ricardo Leitner]

On Wed, Jul 22, 2020 at 11:22:23AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    4f1b4da5 Merge branch 'net-atlantic-various-features'
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x\x14b3a040900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x+7b67c0c1819c87
> dashboard link: https://syzkaller.appspot.com/bug?extid\x0e4699d000d8b874d8dc
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x\x14c93358900000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x\x14ab61f0900000

The syz repo has:
setsockopt$inet_sctp6_SCTP_MAX_BURST(r0, 0x84, 0x10, &(0x7f0000000100)=@assoc_value, 0x8)
                      ^^^^^^^^^^^^^^           ^^^^

#define SCTP_DELAYED_ACK_TIME   16
#define SCTP_DELAYED_ACK SCTP_DELAYED_ACK_TIME
#define SCTP_DELAYED_SACK SCTP_DELAYED_ACK_TIME
#define SCTP_MAX_BURST  20              /* Set/Get max burst */

C repro has:
  syscall(__NR_setsockopt, r[0], 0x84, 0x10, 0x20000100ul, 8ul);
                                       ^^^^

So I'm wondering, what was the real intention of the call?


Anyhow, the issue is real, introduced by ebb25defdc17 ("sctp: pass a
kernel pointer to sctp_setsockopt_delayed_ack"). It used to use a
local storage bigger than the data provided by the user and used
one struct to read another's content on top of it. Quite masked.
I'll cook a fix.

  Marcelo