KASAN: use-after-free Read in copy_to_iter

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 74fa0af4 BACKPORT: dma-buf/sync_file: Allow multiple sync_..
git tree: android-4.9
console output: https://syzkaller.appspot.com/x/log.txt?x=17a17107800000
kernel config: https://syzkaller.appspot.com/x/.config?x=f3ab3f1c4014fe13
dashboard link: https://syzkaller.appspot.com/bug?extid=e454958b7dc8cb86d0ed
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17efe477800000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10c6ae37800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e45495...@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
protocol 0000 is buggy, dev sit0
==================================================================
BUG: KASAN: use-after-free in __copy_to_user
arch/x86/include/asm/uaccess_64.h:182 [inline]
BUG: KASAN: use-after-free in copy_to_iter+0x239/0x10e0 lib/iov_iter.c:540
Read of size 12 at addr ffff8801da2dfc00 by task syz-executor891/4066

CPU: 0 PID: 4066 Comm: syz-executor891 Not tainted 4.9.99-g74fa0af4 #24
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
ffff8801d78475f8 ffffffff81eb0f09 ffffea000768b780 ffff8801da2dfc00
0000000000000000 ffff8801da2dfc00 ffff8801da2dfc00 ffff8801d7847630
ffffffff815652eb ffff8801da2dfc00 000000000000000c 0000000000000000
Call Trace:
[<ffffffff81eb0f09>] __dump_stack lib/dump_stack.c:15 [inline]
[<ffffffff81eb0f09>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
[<ffffffff815652eb>] print_address_description+0x6c/0x234
mm/kasan/report.c:256
[<ffffffff815656f5>] kasan_report_error mm/kasan/report.c:355 [inline]
[<ffffffff815656f5>] kasan_report.cold.6+0x242/0x2fe mm/kasan/report.c:412
[<ffffffff815381df>] check_memory_region_inline mm/kasan/kasan.c:318
[inline]
[<ffffffff815381df>] check_memory_region+0x14f/0x1b0 mm/kasan/kasan.c:325
[<ffffffff81538251>] kasan_check_read+0x11/0x20 mm/kasan/kasan.c:330
[<ffffffff81efa429>] __copy_to_user arch/x86/include/asm/uaccess_64.h:182
[inline]
[<ffffffff81efa429>] copy_to_iter+0x239/0x10e0 lib/iov_iter.c:540
[<ffffffff8304b261>] skb_copy_datagram_iter+0x1d1/0x8f0
net/core/datagram.c:390
[<ffffffff83689573>] skb_copy_datagram_msg include/linux/skbuff.h:3049
[inline]
[<ffffffff83689573>] packet_recvmsg+0x263/0xf40 net/packet/af_packet.c:3359
[<ffffffff830124c6>] sock_recvmsg_nosec net/socket.c:737 [inline]
[<ffffffff830124c6>] sock_recvmsg+0xc6/0x110 net/socket.c:744
[<ffffffff8301275a>] sock_read_iter+0x24a/0x360 net/socket.c:821
[<ffffffff8156e341>] do_iter_readv_writev+0x301/0x4b0 fs/read_write.c:693
[<ffffffff81570856>] do_readv_writev+0x2f6/0x7a0 fs/read_write.c:871
[<ffffffff81570d84>] vfs_readv+0x84/0xc0 fs/read_write.c:897
[<ffffffff81570ea6>] do_readv+0xe6/0x260 fs/read_write.c:923
[<ffffffff81574707>] SYSC_readv fs/read_write.c:1010 [inline]
[<ffffffff81574707>] SyS_readv+0x27/0x30 fs/read_write.c:1007
[<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
[<ffffffff839f4653>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Allocated by task 4067:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
save_stack+0x43/0xd0 mm/kasan/kasan.c:505
set_track mm/kasan/kasan.c:517 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:609
kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:547
slab_post_alloc_hook mm/slab.h:417 [inline]
slab_alloc_node mm/slub.c:2715 [inline]
slab_alloc mm/slub.c:2723 [inline]
__kmalloc_track_caller+0xdc/0x2b0 mm/slub.c:4232
__kmalloc_reserve.isra.37+0x33/0xc0 net/core/skbuff.c:138
__alloc_skb+0x11a/0x600 net/core/skbuff.c:231
alloc_skb include/linux/skbuff.h:919 [inline]
alloc_skb_with_frags+0xaf/0x520 net/core/skbuff.c:4678
sock_alloc_send_pskb+0x5a9/0x750 net/core/sock.c:1893
packet_alloc_skb net/packet/af_packet.c:2817 [inline]
packet_snd net/packet/af_packet.c:2908 [inline]
packet_sendmsg+0x1581/0x4470 net/packet/af_packet.c:2985
sock_sendmsg_nosec net/socket.c:635 [inline]
sock_sendmsg+0xcc/0x110 net/socket.c:645
SYSC_sendto+0x21c/0x370 net/socket.c:1670
SyS_sendto+0x40/0x50 net/socket.c:1638
do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Freed by task 4067:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
save_stack+0x43/0xd0 mm/kasan/kasan.c:505
set_track mm/kasan/kasan.c:517 [inline]
kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:582
slab_free_hook mm/slub.c:1355 [inline]
slab_free_freelist_hook mm/slub.c:1377 [inline]
slab_free mm/slub.c:2958 [inline]
kfree+0xfb/0x310 mm/slub.c:3878
skb_free_head+0x8b/0xb0 net/core/skbuff.c:580
skb_release_data+0x329/0x400 net/core/skbuff.c:611
skb_release_all+0x4a/0x60 net/core/skbuff.c:670
__kfree_skb+0x15/0x20 net/core/skbuff.c:684
kfree_skb+0xcc/0x340 net/core/skbuff.c:705
sit_tunnel_xmit+0xfb/0x2590 net/ipv6/sit.c:1033
__netdev_start_xmit include/linux/netdevice.h:4062 [inline]
netdev_start_xmit include/linux/netdevice.h:4071 [inline]
xmit_one net/core/dev.c:2955 [inline]
dev_hard_start_xmit+0x197/0x8b0 net/core/dev.c:2971
__dev_queue_xmit+0x19a5/0x2080 net/core/dev.c:3451
dev_queue_xmit+0x17/0x20 net/core/dev.c:3484
packet_snd net/packet/af_packet.c:2960 [inline]
packet_sendmsg+0x1eff/0x4470 net/packet/af_packet.c:2985
sock_sendmsg_nosec net/socket.c:635 [inline]
sock_sendmsg+0xcc/0x110 net/socket.c:645
SYSC_sendto+0x21c/0x370 net/socket.c:1670
SyS_sendto+0x40/0x50 net/socket.c:1638
do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
entry_SYSCALL_64_after_swapgs+0x5d/0xdb

The buggy address belongs to the object at ffff8801da2dfb80
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
512-byte region [ffff8801da2dfb80, ffff8801da2dfd80)
The buggy address belongs to the page:
page:ffffea000768b780 count:1 mapcount:0 mapping: (null) index:0x0
compound_mapcount: 0
flags: 0x8000000000004080(slab|head)
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801da2dfb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801da2dfb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801da2dfc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801da2dfc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801da2dfd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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