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SubjectKASAN: use-after-free Read in path_lookupat
From
Hello,

syzbot found the following crash on:

HEAD commit: 442b8cea2477 Add linux-next specific files for 20181109
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=129574db400000
kernel config: https://syzkaller.appspot.com/x/.config?x=2f72bdb11df9fbe8
dashboard link: https://syzkaller.appspot.com/bug?extid=7a8ba368b47fdefca61e
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=132815f5400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7a8ba368b47fdefca61e@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KASAN: use-after-free in lookup_last fs/namei.c:2269 [inline]
BUG: KASAN: use-after-free in path_lookupat.isra.43+0x9f8/0xc00
fs/namei.c:2318
Read of size 1 at addr ffff8801c4865c47 by task syz-executor2/9423

CPU: 0 PID: 9423 Comm: syz-executor2 Not tainted 4.20.0-rc1-next-20181109+
#110
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+0x244/0x39d lib/dump_stack.c:113
print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
lookup_last fs/namei.c:2269 [inline]
path_lookupat.isra.43+0x9f8/0xc00 fs/namei.c:2318
filename_lookup+0x26a/0x520 fs/namei.c:2348
user_path_at_empty+0x40/0x50 fs/namei.c:2608
user_path include/linux/namei.h:62 [inline]
do_mount+0x180/0x1ff0 fs/namespace.c:2980
ksys_mount+0x12d/0x140 fs/namespace.c:3258
__do_sys_mount fs/namespace.c:3272 [inline]
__se_sys_mount fs/namespace.c:3269 [inline]
__x64_sys_mount+0xbe/0x150 fs/namespace.c:3269
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 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 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fde6ed96c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000457569
RDX: 0000000020000040 RSI: 0000000020000000 RDI: 0000000000000000
RBP: 000000000072bf00 R08: 0000000020000340 R09: 0000000000000000
R10: 0000000000200000 R11: 0000000000000246 R12: 00007fde6ed976d4
R13: 00000000004c2c24 R14: 00000000004d4990 R15: 00000000ffffffff

Allocated by task 9424:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
__do_kmalloc mm/slab.c:3722 [inline]
__kmalloc_track_caller+0x157/0x760 mm/slab.c:3737
kstrdup+0x39/0x70 mm/util.c:49
bpf_symlink+0x26/0x140 kernel/bpf/inode.c:356
vfs_symlink+0x37a/0x5d0 fs/namei.c:4127
do_symlinkat+0x242/0x2d0 fs/namei.c:4154
__do_sys_symlink fs/namei.c:4173 [inline]
__se_sys_symlink fs/namei.c:4171 [inline]
__x64_sys_symlink+0x59/0x80 fs/namei.c:4171
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9425:
save_stack+0x43/0xd0 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]
kfree+0xcf/0x230 mm/slab.c:3817
bpf_evict_inode+0x11f/0x150 kernel/bpf/inode.c:565
evict+0x4b9/0x980 fs/inode.c:558
iput_final fs/inode.c:1550 [inline]
iput+0x674/0xa90 fs/inode.c:1576
do_unlinkat+0x733/0xa30 fs/namei.c:4069
__do_sys_unlink fs/namei.c:4110 [inline]
__se_sys_unlink fs/namei.c:4108 [inline]
__x64_sys_unlink+0x42/0x50 fs/namei.c:4108
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801c4865c40
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 7 bytes inside of
32-byte region [ffff8801c4865c40, ffff8801c4865c60)
The buggy address belongs to the page:
page:ffffea0007121940 count:1 mapcount:0 mapping:ffff8801da8001c0
index:0xffff8801c4865fc1
flags: 0x2fffc0000000200(slab)
raw: 02fffc0000000200 ffffea000763c048 ffffea000762cf08 ffff8801da8001c0
raw: ffff8801c4865fc1 ffff8801c4865000 000000010000003f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801c4865b00: fb fb fb fb fc fc fc fc 05 fc fc fc fc fc fc fc
ffff8801c4865b80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
> ffff8801c4865c00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
^
ffff8801c4865c80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
ffff8801c4865d00: fb fb fb fb fc fc fc fc 05 fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
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