syzbot


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

Status: fixed on 2018/01/11 01:23
Subsystems: lsm
[Documentation on labels]
Reported-by: syzbot+37db7b2a61b64a9abb81@syzkaller.appspotmail.com
Fix commit: dc32b5c3e6e2 capabilities: fix buffer overread on very short xattr
First crash: 2336d, last: 2332d
Discussions (1)
Title Replies (including bot) Last reply
KASAN: slab-out-of-bounds Read in cap_inode_getsecurity 1 (2) 2018/01/05 04:54

Sample crash report:
audit: type=1400 audit(1514753657.623:7): avc:  denied  { map } for  pid=3504 comm="syzkaller926656" path="/root/syzkaller926656864" dev="sda1" ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
==================================================================
BUG: KASAN: slab-out-of-bounds in cap_inode_getsecurity+0x621/0x7d0 security/commoncap.c:408
Read of size 4 at addr ffff8801bea30b00 by task syzkaller926656/3504

CPU: 1 PID: 3504 Comm: syzkaller926656 Not tainted 4.15.0-rc5+ #244
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
 cap_inode_getsecurity+0x621/0x7d0 security/commoncap.c:408
 security_inode_getsecurity+0xcd/0x110 security/security.c:809
 xattr_getsecurity+0xd3/0x1f0 fs/xattr.c:244
 vfs_getxattr+0xc8/0x110 fs/xattr.c:333
 getxattr+0x116/0x2a0 fs/xattr.c:540
 path_getxattr+0xed/0x170 fs/xattr.c:568
 SYSC_getxattr fs/xattr.c:580 [inline]
 SyS_getxattr+0x33/0x40 fs/xattr.c:577
 entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x43fd09
RSP: 002b:00007ffcf95c1178 EFLAGS: 00000217 ORIG_RAX: 00000000000000bf
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 000000000043fd09
RDX: 0000000020227f74 RSI: 0000000020b29f57 RDI: 000000002072d000
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000008c R11: 0000000000000217 R12: 0000000000401670
R13: 0000000000401700 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 3504:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
 __do_kmalloc mm/slab.c:3708 [inline]
 __kmalloc_track_caller+0x15e/0x760 mm/slab.c:3723
 __do_krealloc mm/slab_common.c:1407 [inline]
 krealloc+0x65/0xc0 mm/slab_common.c:1454
 vfs_getxattr_alloc+0x177/0x270 fs/xattr.c:290
 cap_inode_getsecurity+0xfa/0x7d0 security/commoncap.c:399
 security_inode_getsecurity+0xcd/0x110 security/security.c:809
 xattr_getsecurity+0xd3/0x1f0 fs/xattr.c:244
 vfs_getxattr+0xc8/0x110 fs/xattr.c:333
 getxattr+0x116/0x2a0 fs/xattr.c:540
 path_getxattr+0xed/0x170 fs/xattr.c:568
 SYSC_getxattr fs/xattr.c:580 [inline]
 SyS_getxattr+0x33/0x40 fs/xattr.c:577
 entry_SYSCALL_64_fastpath+0x23/0x9a

Freed by task 1970:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3488 [inline]
 kfree+0xd6/0x260 mm/slab.c:3803
 single_release+0x88/0xb0 fs/seq_file.c:603
 __fput+0x327/0x7e0 fs/file_table.c:210
 ____fput+0x15/0x20 fs/file_table.c:244
 task_work_run+0x199/0x270 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x296/0x310 arch/x86/entry/common.c:162
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264
 entry_SYSCALL_64_fastpath+0x98/0x9a

The buggy address belongs to the object at ffff8801bea30b00
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes inside of
 32-byte region [ffff8801bea30b00, ffff8801bea30b20)
The buggy address belongs to the page:
page:00000000bdc64004 count:1 mapcount:0 mapping:00000000f92bbf6b index:0xffff8801bea30fc1
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801bea30000 ffff8801bea30fc1 000000010000003f
raw: ffffea0006fa4ea0 ffffea0006fa54e0 ffff8801dac001c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801bea30a00: fb fb fb fb fc fc fc fc 00 00 00 fc fc fc fc fc
 ffff8801bea30a80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>ffff8801bea30b00: 01 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
                   ^
 ffff8801bea30b80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8801bea30c00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
==================================================================

Crashes (11):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2017/12/31 20:56 upstream 71ee203389f7 00193447 .config console log report syz C ci-upstream-kasan-gce
2017/12/31 17:26 upstream 71ee203389f7 00193447 .config console log report syz C ci-upstream-kasan-gce-386
2017/12/31 19:03 linux-next 0e08c463db38 00193447 .config console log report syz C ci-upstream-next-kasan-gce
2017/12/31 16:09 mmots 37759fa6d0fa 00193447 .config console log report syz C ci-upstream-mmots-kasan-gce
2018/01/01 04:30 upstream 30a7acd57389 00193447 .config console log report ci-upstream-kasan-gce
2018/01/05 14:01 mmots ad036b63ee57 00193447 .config console log report ci-upstream-mmots-kasan-gce
2018/01/05 13:35 mmots ad036b63ee57 00193447 .config console log report ci-upstream-mmots-kasan-gce
2018/01/05 01:52 mmots ad036b63ee57 00193447 .config console log report ci-upstream-mmots-kasan-gce
2018/01/04 17:31 linux-next 73005e1a35fd 00193447 .config console log report ci-upstream-next-kasan-gce
2018/01/04 14:36 linux-next 73005e1a35fd 00193447 .config console log report ci-upstream-next-kasan-gce
2017/12/31 19:01 mmots 37759fa6d0fa 00193447 .config console log report ci-upstream-mmots-kasan-gce
* Struck through repros no longer work on HEAD.