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

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: d71f695c Linux 4.14.179
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=17af3b7c100000
kernel config: https://syzkaller.appspot.com/x/.config?x=580f01c69a690433
dashboard link: https://syzkaller.appspot.com/bug?extid=46b335932d55c81f96bd
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+46b335...@syzkaller.appspotmail.com

alloc_fd: slot 3 not NULL!
==================================================================
BUG: KASAN: slab-out-of-bounds in __read_once_size include/linux/compiler.h:183 [inline]
BUG: KASAN: slab-out-of-bounds in __fcheck_files include/linux/fdtable.h:88 [inline]
BUG: KASAN: slab-out-of-bounds in __fget_light+0x1ea/0x1f0 fs/file.c:739
Read of size 8 at addr ffff88800010a7c0 by task syz-executor.0/20611

CPU: 1 PID: 20611 Comm: syz-executor.0 Not tainted 4.14.179-syzkaller #0
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+0x13e/0x194 lib/dump_stack.c:58
print_address_description.cold+0x7c/0x1e2 mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report mm/kasan/report.c:409 [inline]
kasan_report.cold+0xa9/0x2ae mm/kasan/report.c:393
__read_once_size include/linux/compiler.h:183 [inline]
__fcheck_files include/linux/fdtable.h:88 [inline]
__fget_light+0x1ea/0x1f0 fs/file.c:739
__fdget fs/file.c:752 [inline]
__fdget_pos+0x18/0xc0 fs/file.c:763
fdget_pos include/linux/file.h:67 [inline]
SYSC_read fs/read_write.c:569 [inline]
SyS_read+0x63/0x210 fs/read_write.c:567
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4163a0
RSP: 002b:00007ffd93924528 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004163a0
RDX: 00000000000003e8 RSI: 00007ffd93924540 RDI: 00000000000000f0
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000004
R10: 0000000000000075 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffd93924970 R14: 0000000000000000 R15: 00007ffd93924980

Allocated by task 6337:
save_stack+0x32/0xa0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc mm/kasan/kasan.c:551 [inline]
kasan_kmalloc+0xbf/0xe0 mm/kasan/kasan.c:529
__do_kmalloc_node mm/slab.c:3682 [inline]
__kmalloc_node+0x4c/0x70 mm/slab.c:3689
kmalloc_node include/linux/slab.h:530 [inline]
kvmalloc_node+0x46/0xd0 mm/util.c:397
kvmalloc include/linux/mm.h:531 [inline]
xt_alloc_table_info+0x6a/0xe0 net/netfilter/x_tables.c:1062
do_replace net/ipv6/netfilter/ip6_tables.c:1146 [inline]
do_ip6t_set_ctl+0x1b1/0x3a3 net/ipv6/netfilter/ip6_tables.c:1685
nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
nf_setsockopt+0x5f/0xb0 net/netfilter/nf_sockopt.c:115
ipv6_setsockopt net/ipv6/ipv6_sockglue.c:935 [inline]
ipv6_setsockopt+0xfd/0x130 net/ipv6/ipv6_sockglue.c:919
tcp_setsockopt net/ipv4/tcp.c:2826 [inline]
tcp_setsockopt+0x7b/0xc0 net/ipv4/tcp.c:2820
SYSC_setsockopt net/socket.c:1865 [inline]
SyS_setsockopt+0x110/0x1e0 net/socket.c:1844
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 6337:
save_stack+0x32/0xa0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3496 [inline]
kfree+0xcb/0x260 mm/slab.c:3815
kvfree+0x45/0x50 mm/util.c:416
__do_replace+0x3f6/0x580 net/ipv6/netfilter/ip6_tables.c:1107
do_replace net/ipv6/netfilter/ip6_tables.c:1161 [inline]
do_ip6t_set_ctl+0x255/0x3a3 net/ipv6/netfilter/ip6_tables.c:1685
nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
nf_setsockopt+0x5f/0xb0 net/netfilter/nf_sockopt.c:115
ipv6_setsockopt net/ipv6/ipv6_sockglue.c:935 [inline]
ipv6_setsockopt+0xfd/0x130 net/ipv6/ipv6_sockglue.c:919
tcp_setsockopt net/ipv4/tcp.c:2826 [inline]
tcp_setsockopt+0x7b/0xc0 net/ipv4/tcp.c:2820
SYSC_setsockopt net/socket.c:1865 [inline]
SyS_setsockopt+0x110/0x1e0 net/socket.c:1844
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff88800010a040
which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1920 bytes inside of
2048-byte region [ffff88800010a040, ffff88800010a840)
The buggy address belongs to the page:
page:ffffea0000004280 count:1 mapcount:0 mapping:ffff88800010a040 index:0x0 compound_mapcount: 0
flags: 0x7ffe0000008100(slab|head)
raw: 007ffe0000008100 ffff88800010a040 0000000000000000 0000000100000003
raw: ffffea0002530a20 ffffea000246faa0 ffff88812fe54c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88800010a680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88800010a700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88800010a780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88800010a800: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff88800010a880: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.