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SubjectKMSAN: kernel-infoleak in copyout (2)
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Hello,

syzbot found the following crash on:

HEAD commit: 686a4f77 kmsan: don't compile memmove
git tree: https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=13235a31e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=e10654781bc1f11c
dashboard link: https://syzkaller.appspot.com/bug?extid=fa5414772d5c445dac3c
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=164789e9e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1014a229e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+fa5414772d5c445dac3c@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak in kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:253
CPU: 1 PID: 11522 Comm: syz-executor835 Not tainted 5.5.0-rc5-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:253
copyout+0x15a/0x1e0 lib/iov_iter.c:145
_copy_to_iter+0x34e/0x2420 lib/iov_iter.c:633
copy_to_iter include/linux/uio.h:138 [inline]
simple_copy_to_iter+0xd7/0x130 net/core/datagram.c:515
__skb_datagram_iter+0x25f/0xfc0 net/core/datagram.c:423
skb_copy_datagram_iter+0x292/0x2b0 net/core/datagram.c:529
tun_put_user drivers/net/tun.c:2144 [inline]
tun_do_read+0x2471/0x2df0 drivers/net/tun.c:2228
tun_chr_read_iter+0x229/0x460 drivers/net/tun.c:2247
call_read_iter include/linux/fs.h:1896 [inline]
new_sync_read fs/read_write.c:414 [inline]
__vfs_read+0xa64/0xc80 fs/read_write.c:427
vfs_read+0x346/0x6a0 fs/read_write.c:461
ksys_read+0x267/0x450 fs/read_write.c:587
__do_sys_read fs/read_write.c:597 [inline]
__se_sys_read+0x92/0xb0 fs/read_write.c:595
__x64_sys_read+0x4a/0x70 fs/read_write.c:595
do_syscall_64+0xb8/0x160 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x403f40
Code: 01 f0 ff ff 0f 83 a0 0d 00 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 83 3d 6d a0 2d 00 00 75 14 b8 00 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 74 0d 00 00 c3 48 83 ec 08 e8 da 02 00 00
RSP: 002b:00007ffe8e33e1d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000403f40
RDX: 00000000000003e8 RSI: 00007ffe8e33e1e0 RDI: 00000000000000f0
RBP: 000000000002640f R08: 0000000000000000 R09: 0000000000000004
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00000000004051d0 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:1637
__skb_cow include/linux/skbuff.h:3120 [inline]
skb_cow_head include/linux/skbuff.h:3154 [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:1706
process_one_work+0x1552/0x1ef0 kernel/workqueue.c:2264
worker_thread+0xef6/0x2450 kernel/workqueue.c:2410
kthread+0x4b5/0x4f0 kernel/kthread.c:256
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:307 [inline]
kmsan_alloc_page+0x12a/0x310 mm/kmsan/kmsan_shadow.c:336
__alloc_pages_nodemask+0x57f2/0x5f60 mm/page_alloc.c:4800
__alloc_pages include/linux/gfp.h:498 [inline]
__alloc_pages_node include/linux/gfp.h:511 [inline]
alloc_pages_node include/linux/gfp.h:525 [inline]
__page_frag_cache_refill mm/page_alloc.c:4875 [inline]
page_frag_alloc+0x3ae/0x910 mm/page_alloc.c:4905
__netdev_alloc_skb+0x703/0xbb0 net/core/skbuff.c:455
__netdev_alloc_skb_ip_align include/linux/skbuff.h:2801 [inline]
netdev_alloc_skb_ip_align include/linux/skbuff.h:2811 [inline]
batadv_iv_ogm_aggregate_new net/batman-adv/bat_iv_ogm.c:558 [inline]
batadv_iv_ogm_queue_add+0x10da/0x1900 net/batman-adv/bat_iv_ogm.c:670
batadv_iv_ogm_schedule_buff net/batman-adv/bat_iv_ogm.c:845 [inline]
batadv_iv_ogm_schedule+0x107b/0x13c0 net/batman-adv/bat_iv_ogm.c:865
batadv_iv_send_outstanding_bat_ogm_packet+0xbae/0xd50 net/batman-adv/bat_iv_ogm.c:1718
process_one_work+0x1552/0x1ef0 kernel/workqueue.c:2264
worker_thread+0xef6/0x2450 kernel/workqueue.c:2410
kthread+0x4b5/0x4f0 kernel/kthread.c:256
ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:353

Bytes 52-53 of 146 are uninitialized
Memory access of size 146 starts at ffff9ecbf8eb0c40
Data copied to user address 00007ffe8e33e1e0
=====================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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