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

[syzbot]

Hello,

syzkaller hit the following crash on
71ee203389f7cb1c1927eab22b95baa01405791c
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+37db7b...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.

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
==================================================================


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzk...@googlegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is
merged
into any tree, please reply to this email with:
#syz fix: exact-commit-title
If you want to test a patch for this bug, please reply with:
#syz test: git://repo/address.git branch
and provide the patch inline or as an attachment.
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug
report.
Note: all commands must start from beginning of the line in the email body.

[Eric Biggers]

Already fixed in Linus's tree.

#syz fix: capabilities: fix buffer overread on very short xattr