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

syzbot found the following crash on:

HEAD commit: 7c1b097f27bf Add linux-next specific files for 20180912
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14e6101a400000
kernel config: https://syzkaller.appspot.com/x/.config?x=5980033172920ec0
dashboard link: https://syzkaller.appspot.com/bug?extid=fef0b74a3bf760a9ee85
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13104f71400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+fef0b74a3bf760a9ee85@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: cc1: uninitialized urandom read (8 bytes read)
==================================================================
BUG: KASAN: use-after-free in mqueue_get_tree+0x2ac/0x2e0 ipc/mqueue.c:362
Read of size 8 at addr ffff8801d7cc0688 by task syz-executor4/5584

CPU: 0 PID: 5584 Comm: syz-executor4 Not tainted 4.19.0-rc3-next-20180912+
#72
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+0x1d3/0x2c4 lib/dump_stack.c:113
print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
mqueue_get_tree+0x2ac/0x2e0 ipc/mqueue.c:362
vfs_get_tree+0x1cb/0x5c0 fs/super.c:1787
mq_create_mount+0xe3/0x190 ipc/mqueue.c:415
mq_init_ns+0x15a/0x210 ipc/mqueue.c:1621
create_ipc_ns ipc/namespace.c:58 [inline]
copy_ipcs+0x3d2/0x580 ipc/namespace.c:84
create_new_namespaces+0x376/0x900 kernel/nsproxy.c:87
unshare_nsproxy_namespaces+0xc3/0x1f0 kernel/nsproxy.c:206
ksys_unshare+0x79c/0x10b0 kernel/fork.c:2535
__do_sys_unshare kernel/fork.c:2603 [inline]
__se_sys_unshare kernel/fork.c:2601 [inline]
__x64_sys_unshare+0x31/0x40 kernel/fork.c:2601
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459d87
Code: 00 00 00 b8 63 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 3d 8a fb ff c3
66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 10 01 00 00 0f 05 <48> 3d 01 f0 ff
ff 0f 83 1d 8a fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffddc9e7fb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459d87
RDX: 0000000000000000 RSI: 00007ffddc9e7fc0 RDI: 0000000008000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000018
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000412c30
R13: 0000000000412cc0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 3455:
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
kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554
getname_flags+0xd0/0x5a0 fs/namei.c:140
getname fs/namei.c:211 [inline]
do_symlinkat+0x8b/0x2d0 fs/namei.c:4143
__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 3455:
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]
kmem_cache_free+0x83/0x290 mm/slab.c:3756
putname+0xf2/0x130 fs/namei.c:261
do_symlinkat+0x18c/0x2d0 fs/namei.c:4161
__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

The buggy address belongs to the object at ffff8801d7cc0540
which belongs to the cache names_cache of size 4096
The buggy address is located 328 bytes inside of
4096-byte region [ffff8801d7cc0540, ffff8801d7cc1540)
The buggy address belongs to the page:
page:ffffea00075f3000 count:1 mapcount:0 mapping:ffff8801da972d80 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffffea00075fa788 ffffea00075f0b08 ffff8801da972d80
raw: 0000000000000000 ffff8801d7cc0540 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d7cc0580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d7cc0600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801d7cc0680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801d7cc0700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d7cc0780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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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