syzbot


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

Status: fixed on 2020/05/10 10:42
Reported-by: syzbot+9bc8c4f42b3e1d0274fe@syzkaller.appspotmail.com
Fix commit: a1a7e3a36e01 xfrm: add the missing verify_sec_ctx_len check in xfrm_add_acquire
First crash: 818d, last: 818d

Cause bisection: the issue happens on the oldest tested release (bisect log)
Crash: WARNING in sysfs_warn_dup (log)
Repro: C syz .config
similar bugs (2):
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.14 KASAN: slab-out-of-bounds Read in selinux_xfrm_alloc_user C done 1 824d 824d 1/1 fixed on 2020/04/21 23:14
linux-4.19 KASAN: slab-out-of-bounds Read in selinux_xfrm_alloc_user C done 3 831d 836d 1/1 fixed on 2020/04/16 05:11

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:381 [inline]
BUG: KASAN: slab-out-of-bounds in selinux_xfrm_alloc_user+0x23e/0x450 security/selinux/xfrm.c:99
Read of size 768 at addr ffff88808d161934 by task syz-executor391/7036

CPU: 0 PID: 7036 Comm: syz-executor391 Not tainted 5.6.0-rc7-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+0x188/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd3/0x315 mm/kasan/report.c:374
 __kasan_report.cold+0x1a/0x32 mm/kasan/report.c:506
 kasan_report+0xe/0x20 mm/kasan/common.c:641
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x128/0x190 mm/kasan/generic.c:192
 memcpy+0x20/0x50 mm/kasan/common.c:127
 memcpy include/linux/string.h:381 [inline]
 selinux_xfrm_alloc_user+0x23e/0x450 security/selinux/xfrm.c:99
 security_xfrm_policy_alloc+0x6c/0xb0 security/security.c:2263
 copy_from_user_sec_ctx net/xfrm/xfrm_user.c:1462 [inline]
 xfrm_policy_construct+0x2a8/0x660 net/xfrm/xfrm_user.c:1627
 xfrm_add_acquire+0x215/0x9f0 net/xfrm/xfrm_user.c:2280
 xfrm_user_rcv_msg+0x414/0x700 net/xfrm/xfrm_user.c:2676
 netlink_rcv_skb+0x15a/0x410 net/netlink/af_netlink.c:2469
 xfrm_netlink_rcv+0x6b/0x90 net/xfrm/xfrm_user.c:2684
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x537/0x740 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x882/0xe10 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:672
 ____sys_sendmsg+0x6b9/0x7d0 net/socket.c:2345
 ___sys_sendmsg+0x100/0x170 net/socket.c:2399
 __sys_sendmsg+0xec/0x1b0 net/socket.c:2432
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4405f9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffabe06278 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004405f9
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401e80
R13: 0000000000401f10 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 7036:
 save_stack+0x1b/0x80 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc mm/kasan/common.c:515 [inline]
 __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:488
 __kmalloc_reserve.isra.0+0x39/0xe0 net/core/skbuff.c:142
 __alloc_skb+0xef/0x5a0 net/core/skbuff.c:210
 alloc_skb include/linux/skbuff.h:1083 [inline]
 netlink_alloc_large_skb net/netlink/af_netlink.c:1175 [inline]
 netlink_sendmsg+0x97b/0xe10 net/netlink/af_netlink.c:1893
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:672
 ____sys_sendmsg+0x6b9/0x7d0 net/socket.c:2345
 ___sys_sendmsg+0x100/0x170 net/socket.c:2399
 __sys_sendmsg+0xec/0x1b0 net/socket.c:2432
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 5010:
 save_stack+0x1b/0x80 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:337 [inline]
 __kasan_slab_free+0xf7/0x140 mm/kasan/common.c:476
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x109/0x2b0 mm/slab.c:3757
 skb_free_head+0x8b/0xa0 net/core/skbuff.c:590
 skb_release_data+0x42e/0x8b0 net/core/skbuff.c:610
 skb_release_all+0x46/0x60 net/core/skbuff.c:664
 __kfree_skb net/core/skbuff.c:678 [inline]
 consume_skb net/core/skbuff.c:837 [inline]
 consume_skb+0xf3/0x400 net/core/skbuff.c:831
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x53f/0x740 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x882/0xe10 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:672
 ____sys_sendmsg+0x6b9/0x7d0 net/socket.c:2345
 ___sys_sendmsg+0x100/0x170 net/socket.c:2399
 __sys_sendmsg+0xec/0x1b0 net/socket.c:2432
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88808d161800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 308 bytes inside of
 1024-byte region [ffff88808d161800, ffff88808d161c00)
The buggy address belongs to the page:
page:ffffea0002345840 refcount:1 mapcount:0 mapping:ffff8880aa000c40 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00023d3008 ffffea00029cb048 ffff8880aa000c40
raw: 0000000000000000 ffff88808d161000 0000000100000002 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88808d161b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88808d161b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88808d161c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                   ^
 ffff88808d161c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88808d161d00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (1):
Manager Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Title
ci-upstream-kasan-gce-selinux-root 2020/03/29 15:12 upstream 906c40438bb6 05736b29 .config log report syz C