KMSAN: kernel-infoleak in _copy_to_iter (5)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    14bcee29 DO-NOT-SUBMIT: kmsan: block: nullb: handle read r..
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=1752af7c100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6f048d804e1a47a0
dashboard link: https://syzkaller.appspot.com/bug?extid=50ee810676e6a089487b
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10c69b42100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15f72658100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+50ee810676e6a089487b@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
BUG: KMSAN: kernel-infoleak in kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:251
CPU: 0 PID: 9041 Comm: syz-executor493 Not tainted 5.7.0-rc4-syzkaller #0
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+0x1c9/0x220 lib/dump_stack.c:118
 kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118
 kmsan_internal_check_memory+0x238/0x3d0 mm/kmsan/kmsan.c:423
 kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:251
 copyout lib/iov_iter.c:145 [inline]
 _copy_to_iter+0x44f/0x2770 lib/iov_iter.c:633
 copy_to_iter include/linux/uio.h:138 [inline]
 simple_copy_to_iter net/core/datagram.c:519 [inline]
 __skb_datagram_iter+0x2bb/0x1220 net/core/datagram.c:425
 skb_copy_datagram_iter+0x292/0x2b0 net/core/datagram.c:533
 skb_copy_datagram_msg include/linux/skbuff.h:3537 [inline]
 packet_recvmsg+0x630/0x1c40 net/packet/af_packet.c:3378
 ____sys_recvmsg+0xf58/0x1020 net/socket.c:886
 ___sys_recvmsg net/socket.c:2627 [inline]
 do_recvmmsg+0x990/0x1e00 net/socket.c:2725
 __sys_recvmmsg net/socket.c:2804 [inline]
 __do_sys_recvmmsg net/socket.c:2827 [inline]
 __se_sys_recvmmsg+0x1d1/0x350 net/socket.c:2820
 __x64_sys_recvmmsg+0x62/0x80 net/socket.c:2820
 do_syscall_64+0xb8/0x160 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x443ca9
Code: e8 8c 07 03 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 3b 0a fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffcf6171b28 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000443ca9
RDX: 0000000000000002 RSI: 0000000020000a80 RDI: 0000000000000003
RBP: 00007ffcf6171b30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000000142fb
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Uninit was stored to memory at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
 kmsan_internal_chain_origin+0xad/0x130 mm/kmsan/kmsan.c:310
 kmsan_memcpy_memmove_metadata+0x272/0x2e0 mm/kmsan/kmsan.c:247
 kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:267
 __msan_memcpy+0x43/0x50 mm/kmsan/kmsan_instr.c:116
 pskb_expand_head+0x38b/0x1b00 net/core/skbuff.c:1636
 __skb_cow include/linux/skbuff.h:3171 [inline]
 skb_cow_head include/linux/skbuff.h:3205 [inline]
 batadv_skb_head_push+0x234/0x350 net/batman-adv/soft-interface.c:74
 batadv_send_skb_packet+0x1a7/0x8c0 net/batman-adv/send.c:86
 batadv_send_broadcast_skb+0x76/0x90 net/batman-adv/send.c:127
 batadv_iv_ogm_send_to_if net/batman-adv/bat_iv_ogm.c:393 [inline]
 batadv_iv_ogm_emit net/batman-adv/bat_iv_ogm.c:419 [inline]
 batadv_iv_send_outstanding_bat_ogm_packet+0x97e/0xd50 net/batman-adv/bat_iv_ogm.c:1710
 process_one_work+0x1555/0x1f40 kernel/workqueue.c:2268
 worker_thread+0xef6/0x2450 kernel/workqueue.c:2414
 kthread+0x4b5/0x4f0 kernel/kthread.c:269
 ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:353

Uninit was created at:
 kmsan_save_stack_with_flags+0x3c/0x90 mm/kmsan/kmsan.c:144
 kmsan_internal_alloc_meta_for_pages mm/kmsan/kmsan_shadow.c:280 [inline]
 kmsan_alloc_page+0xb9/0x180 mm/kmsan/kmsan_shadow.c:304
 __alloc_pages_nodemask+0x56a2/0x5dc0 mm/page_alloc.c:4848
 __alloc_pages include/linux/gfp.h:504 [inline]
 __alloc_pages_node include/linux/gfp.h:517 [inline]
 alloc_pages_node include/linux/gfp.h:531 [inline]
 __page_frag_cache_refill mm/page_alloc.c:4923 [inline]
 page_frag_alloc+0x3ae/0x910 mm/page_alloc.c:4953
 __napi_alloc_skb+0x193/0xa60 net/core/skbuff.c:519
 napi_alloc_skb include/linux/skbuff.h:2876 [inline]
 page_to_skb+0x1a2/0x1390 drivers/net/virtio_net.c:384
 receive_mergeable drivers/net/virtio_net.c:935 [inline]
 receive_buf+0xed6/0x8d50 drivers/net/virtio_net.c:1045
 virtnet_receive drivers/net/virtio_net.c:1335 [inline]
 virtnet_poll+0x64b/0x19f0 drivers/net/virtio_net.c:1440
 napi_poll net/core/dev.c:6572 [inline]
 net_rx_action+0x786/0x1aa0 net/core/dev.c:6640
 __do_softirq+0x311/0x83d kernel/softirq.c:293

Bytes 52-53 of 146 are uninitialized
Memory access of size 146 starts at ffff898139239040
Data copied to user address 0000000020000980
=====================================================


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