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SubjectKASAN: slab-out-of-bounds Read in __xfrm_policy_bysel_ctx
From
Hello,

syzbot found the following crash on:

HEAD commit: b71acb0e3721 Merge branch 'linus' of git://git.kernel.org/..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15e83920c00000
kernel config: https://syzkaller.appspot.com/x/.config?x=4a8e05cab2dc66d3
dashboard link: https://syzkaller.appspot.com/bug?extid=f8bca486925bdceb2632
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f8bca486925bdceb2632@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in
__xfrm_policy_bysel_ctx.constprop.0+0x3e5/0x470 net/xfrm/xfrm_policy.c:1618
Read of size 1 at addr ffff8880a7a49459 by task syz-executor2/9675

CPU: 0 PID: 9675 Comm: syz-executor2 Not tainted 4.20.0+ #2
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+0x1db/0x2d0 lib/dump_stack.c:113
print_address_description.cold+0x7c/0x20d mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report mm/kasan/report.c:412 [inline]
kasan_report.cold+0x8c/0x2ba mm/kasan/report.c:396
__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
__xfrm_policy_bysel_ctx.constprop.0+0x3e5/0x470 net/xfrm/xfrm_policy.c:1618
xfrm_policy_bysel_ctx+0x944/0x1020 net/xfrm/xfrm_policy.c:1664
xfrm_get_policy+0x67b/0x1160 net/xfrm/xfrm_user.c:1887
xfrm_user_rcv_msg+0x458/0x8d0 net/xfrm/xfrm_user.c:2663
netlink_rcv_skb+0x17d/0x410 net/netlink/af_netlink.c:2477
xfrm_netlink_rcv+0x70/0x90 net/xfrm/xfrm_user.c:2671
netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
netlink_unicast+0x574/0x770 net/netlink/af_netlink.c:1336
netlink_sendmsg+0xa05/0xf90 net/netlink/af_netlink.c:1917
sock_sendmsg_nosec net/socket.c:621 [inline]
sock_sendmsg+0xdd/0x130 net/socket.c:631
___sys_sendmsg+0x7ec/0x910 net/socket.c:2116
__sys_sendmsg+0x112/0x270 net/socket.c:2154
__do_sys_sendmsg net/socket.c:2163 [inline]
__se_sys_sendmsg net/socket.c:2161 [inline]
__x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457ec9
Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f80d9bebc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457ec9
RDX: 0000000000000000 RSI: 000000002014f000 RDI: 0000000000000003
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f80d9bec6d4
R13: 00000000004c5223 R14: 00000000004d8ae8 R15: 00000000ffffffff

Allocated by task 3861:
save_stack+0x45/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc mm/kasan/kasan.c:553 [inline]
kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:531
kasan_slab_alloc+0xf/0x20 mm/kasan/kasan.c:490
kmem_cache_alloc+0x12e/0x700 mm/slab.c:3554
getname_flags fs/namei.c:140 [inline]
getname_flags+0xd6/0x5b0 fs/namei.c:129
getname+0x1a/0x20 fs/namei.c:211
do_sys_open+0x3a5/0x740 fs/open.c:1057
__do_sys_open fs/open.c:1081 [inline]
__se_sys_open fs/open.c:1076 [inline]
__x64_sys_open+0x7e/0xc0 fs/open.c:1076
do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 3861:
save_stack+0x45/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kmem_cache_free+0x86/0x260 mm/slab.c:3760
putname+0xef/0x130 fs/namei.c:261
do_sys_open+0x3f4/0x740 fs/open.c:1072
__do_sys_open fs/open.c:1081 [inline]
__se_sys_open fs/open.c:1076 [inline]
__x64_sys_open+0x7e/0xc0 fs/open.c:1076
do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a7a48200
which belongs to the cache names_cache of size 4096
The buggy address is located 601 bytes to the right of
4096-byte region [ffff8880a7a48200, ffff8880a7a49200)
The buggy address belongs to the page:
page:ffffea00029e9200 count:1 mapcount:0 mapping:ffff88812c2bec40 index:0x0
compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0002a05208 ffffea00021b2f08 ffff88812c2bec40
raw: 0000000000000000 ffff8880a7a48200 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a7a49300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a7a49380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880a7a49400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff8880a7a49480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a7a49500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
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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