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

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 56b697c6 Add linux-next specific files for 20190604
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=170d747ca00000
kernel config: https://syzkaller.appspot.com/x/.config?x=4248d6bc70076f7d
dashboard link: https://syzkaller.appspot.com/bug?extid=9343b7623bc03dc680c1
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+9343b7...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in css_task_iter_advance+0x49b/0x540
kernel/cgroup/cgroup.c:4507
Read of size 4 at addr ffff88809ae59d64 by task syz-executor.2/28895

CPU: 1 PID: 28895 Comm: syz-executor.2 Not tainted 5.2.0-rc3-next-20190604
#8
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+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
__kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
kasan_report+0x12/0x20 mm/kasan/common.c:614
__asan_report_load4_noabort+0x14/0x20 mm/kasan/generic_report.c:131
css_task_iter_advance+0x49b/0x540 kernel/cgroup/cgroup.c:4507
css_task_iter_start+0x18b/0x230 kernel/cgroup/cgroup.c:4543
update_tasks_flags+0x85/0x100 kernel/cgroup/cpuset.c:1836
update_flag+0x232/0x470 kernel/cgroup/cpuset.c:1886
cpuset_write_u64+0x222/0x270 kernel/cgroup/cpuset.c:2268
cgroup_file_write+0x4db/0x790 kernel/cgroup/cgroup.c:3727
kernfs_fop_write+0x2b8/0x480 fs/kernfs/file.c:316
__vfs_write+0x8a/0x110 fs/read_write.c:494
vfs_write+0x268/0x5d0 fs/read_write.c:558
ksys_write+0x14f/0x290 fs/read_write.c:611
__do_sys_write fs/read_write.c:623 [inline]
__se_sys_write fs/read_write.c:620 [inline]
__x64_sys_write+0x73/0xb0 fs/read_write.c:620
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459279
Code: fd 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 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f8d15ef2c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459279
RDX: 0000000000000011 RSI: 00000000200000c0 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f8d15ef36d4
R13: 00000000004c8eb1 R14: 00000000004dfb68 R15: 00000000ffffffff

Allocated by task 9803:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_kmalloc mm/kasan/common.c:489 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:497
slab_post_alloc_hook mm/slab.h:444 [inline]
slab_alloc mm/slab.c:3320 [inline]
kmem_cache_alloc+0x11a/0x6f0 mm/slab.c:3482
getname_flags fs/namei.c:138 [inline]
getname_flags+0xd6/0x5b0 fs/namei.c:128
getname fs/namei.c:209 [inline]
do_renameat2+0x199/0xc40 fs/namei.c:4543
__do_sys_rename fs/namei.c:4671 [inline]
__se_sys_rename fs/namei.c:4669 [inline]
__x64_sys_rename+0x61/0x80 fs/namei.c:4669
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9803:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
__cache_free mm/slab.c:3426 [inline]
kmem_cache_free+0x86/0x320 mm/slab.c:3692
putname+0xef/0x130 fs/namei.c:259
do_renameat2+0x2b4/0xc40 fs/namei.c:4647
__do_sys_rename fs/namei.c:4671 [inline]
__se_sys_rename fs/namei.c:4669 [inline]
__x64_sys_rename+0x61/0x80 fs/namei.c:4669
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88809ae58440
which belongs to the cache names_cache of size 4096
The buggy address is located 2340 bytes to the right of
4096-byte region [ffff88809ae58440, ffff88809ae59440)
The buggy address belongs to the page:
page:ffffea00026b9600 refcount:1 mapcount:0 mapping:ffff8880aa593ac0
index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea00018b4308 ffffea0001afb488 ffff8880aa593ac0
raw: 0000000000000000 ffff88809ae58440 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809ae59c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88809ae59c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff88809ae59d00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88809ae59d80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88809ae59e00: 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.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
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[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: 56b697c6 Add linux-next specific files for 20190604
git tree: linux-next

console output: https://syzkaller.appspot.com/x/log.txt?x=122c965aa00000

kernel config: https://syzkaller.appspot.com/x/.config?x=4248d6bc70076f7d
dashboard link: https://syzkaller.appspot.com/bug?extid=9343b7623bc03dc680c1
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=102ab292a00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15f0e27ca00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+9343b7...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in css_task_iter_advance+0x49b/0x540
kernel/cgroup/cgroup.c:4507

Read of size 4 at addr ffff8880a2013d64 by task syz-executor561/8892

CPU: 0 PID: 8892 Comm: syz-executor561 Not tainted 5.2.0-rc3-next-20190604

#8
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+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
__kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
kasan_report+0x12/0x20 mm/kasan/common.c:614
__asan_report_load4_noabort+0x14/0x20 mm/kasan/generic_report.c:131
css_task_iter_advance+0x49b/0x540 kernel/cgroup/cgroup.c:4507

css_task_iter_next+0x101/0x190 kernel/cgroup/cgroup.c:4569
pidlist_array_load+0x1bf/0xa80 kernel/cgroup/cgroup-v1.c:373
cgroup_pidlist_start+0x37e/0x4c0 kernel/cgroup/cgroup-v1.c:442
cgroup_seqfile_start+0xa4/0xd0 kernel/cgroup/cgroup.c:3752
kernfs_seq_start+0xdc/0x190 fs/kernfs/file.c:118
seq_read+0x2a7/0x1110 fs/seq_file.c:224
kernfs_fop_read+0xed/0x560 fs/kernfs/file.c:252
do_loop_readv_writev fs/read_write.c:714 [inline]
do_loop_readv_writev fs/read_write.c:701 [inline]
do_iter_read+0x4a4/0x660 fs/read_write.c:935
vfs_readv+0xf0/0x160 fs/read_write.c:997
do_preadv+0x1c4/0x280 fs/read_write.c:1089
__do_sys_preadv fs/read_write.c:1139 [inline]
__se_sys_preadv fs/read_write.c:1134 [inline]
__x64_sys_preadv+0x9a/0xf0 fs/read_write.c:1134
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4471c9
Code: e8 4c bb 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 5b 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f7fb370bdb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 00000000006dcc58 RCX: 00000000004471c9
RDX: 0000000000000001 RSI: 0000000020000100 RDI: 0000000000000004
RBP: 00000000006dcc50 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc5c
R13: 00007fffdb647a6f R14: 00007f7fb370c9c0 R15: 0000000000000001

Allocated by task 8773:

save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_kmalloc mm/kasan/common.c:489 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462

kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
__do_kmalloc mm/slab.c:3654 [inline]
__kmalloc+0x15c/0x740 mm/slab.c:3663
kmalloc include/linux/slab.h:552 [inline]
tomoyo_realpath_from_path+0xcd/0x7a0 security/tomoyo/realpath.c:277
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_number_perm+0x1dd/0x520 security/tomoyo/file.c:723
tomoyo_file_ioctl+0x23/0x30 security/tomoyo/tomoyo.c:335
security_file_ioctl+0x77/0xc0 security/security.c:1366
ksys_ioctl+0x57/0xd0 fs/ioctl.c:711
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8773:

save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
__cache_free mm/slab.c:3426 [inline]

kfree+0x106/0x2a0 mm/slab.c:3753
tomoyo_realpath_from_path+0x1de/0x7a0 security/tomoyo/realpath.c:319
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_number_perm+0x1dd/0x520 security/tomoyo/file.c:723
tomoyo_file_ioctl+0x23/0x30 security/tomoyo/tomoyo.c:335
security_file_ioctl+0x77/0xc0 security/security.c:1366
ksys_ioctl+0x57/0xd0 fs/ioctl.c:711
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a20127c0
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1444 bytes to the right of
4096-byte region [ffff8880a20127c0, ffff8880a20137c0)

The buggy address belongs to the page:

page:ffffea0002880480 refcount:1 mapcount:0 mapping:ffff8880aa400dc0

index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)

raw: 01fffc0000010200 ffffea0002311108 ffffea0002885488 ffff8880aa400dc0
raw: 0000000000000000 ffff8880a20127c0 0000000100000001 0000000000000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff8880a2013c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a2013c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880a2013d00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff8880a2013d80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a2013e00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

[syzbot]

syzbot has bisected this bug to:

commit b636fd38dc40113f853337a7d2a6885ad23b8811
Author: Tejun Heo <t...@kernel.org>
Date: Fri May 31 17:38:58 2019 +0000

cgroup: Implement css_task_iter_skip()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1256fcd2a00000
start commit: 56b697c6 Add linux-next specific files for 20190604
git tree: linux-next
final crash: https://syzkaller.appspot.com/x/report.txt?x=1156fcd2a00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1656fcd2a00000

kernel config: https://syzkaller.appspot.com/x/.config?x=4248d6bc70076f7d
dashboard link: https://syzkaller.appspot.com/bug?extid=9343b7623bc03dc680c1

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=102ab292a00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15f0e27ca00000

Reported-by: syzbot+9343b7...@syzkaller.appspotmail.com
Fixes: b636fd38dc40 ("cgroup: Implement css_task_iter_skip()")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Eric Biggers]

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#syz fix: cgroup: Fix css_task_iter_advance_css_set() cset skip condition