[syzbot] [nfc?] UBSAN: shift-out-of-bounds in nci_activate_target
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syzbot
Apr 2, 2023, 12:21:42 PM4/2/23
to da...@davemloft.net, edum...@google.com, krzysztof...@linaro.org, ku...@kernel.org, linux-...@vger.kernel.org, linu...@lists.01.org, net...@vger.kernel.org, pab...@redhat.com, syzkall...@googlegroups.com
Hello,
syzbot found the following issue on:
HEAD commit: 198925fae644 Add linux-next specific files for 20230329
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1174a6d1c80000
kernel config: https://syzkaller.appspot.com/x/.config?x=91e70627549fd509
dashboard link: https://syzkaller.appspot.com/bug?extid=0839b78e119aae1fec78
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/53c685bee82f/disk-198925fa.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/45e82baa3bc5/vmlinux-198925fa.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7c31fbc6acb9/bzImage-198925fa.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0839b7...@syzkaller.appspotmail.com
================================================================================
UBSAN: shift-out-of-bounds in net/nfc/nci/core.c:912:45
shift exponent 4294967071 is too large for 32-bit type 'int'
CPU: 1 PID: 30237 Comm: syz-executor.2 Not tainted 6.3.0-rc4-next-20230329-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x136/0x150 lib/dump_stack.c:106
ubsan_epilogue lib/ubsan.c:217 [inline]
__ubsan_handle_shift_out_of_bounds+0x221/0x5a0 lib/ubsan.c:387
nci_activate_target.cold+0x1a/0x1f net/nfc/nci/core.c:912
nfc_activate_target+0x1f8/0x4c0 net/nfc/core.c:420
nfc_genl_activate_target+0x1f3/0x290 net/nfc/netlink.c:900
genl_family_rcv_msg_doit.isra.0+0x1e6/0x2d0 net/netlink/genetlink.c:968
genl_family_rcv_msg net/netlink/genetlink.c:1048 [inline]
genl_rcv_msg+0x4ff/0x7e0 net/netlink/genetlink.c:1065
netlink_rcv_skb+0x165/0x440 net/netlink/af_netlink.c:2572
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1076
netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline]
netlink_unicast+0x547/0x7f0 net/netlink/af_netlink.c:1365
netlink_sendmsg+0x925/0xe30 net/netlink/af_netlink.c:1942
sock_sendmsg_nosec net/socket.c:724 [inline]
sock_sendmsg+0xde/0x190 net/socket.c:747
____sys_sendmsg+0x71c/0x900 net/socket.c:2501
___sys_sendmsg+0x110/0x1b0 net/socket.c:2555
__sys_sendmsg+0xf7/0x1c0 net/socket.c:2584
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fc4abc8c0f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 90 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc4aca02168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fc4abdabf80 RCX: 00007fc4abc8c0f9
RDX: 0000000000000000 RSI: 0000000020000780 RDI: 0000000000000005
RBP: 00007fc4abce7b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffcb707727f R14: 00007fc4aca02300 R15: 0000000000022000
</TASK>
================================================================================
---
This report 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 syzk...@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot found the following issue on:
HEAD commit: 198925fae644 Add linux-next specific files for 20230329
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1174a6d1c80000
kernel config: https://syzkaller.appspot.com/x/.config?x=91e70627549fd509
dashboard link: https://syzkaller.appspot.com/bug?extid=0839b78e119aae1fec78
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/53c685bee82f/disk-198925fa.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/45e82baa3bc5/vmlinux-198925fa.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7c31fbc6acb9/bzImage-198925fa.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0839b7...@syzkaller.appspotmail.com
================================================================================
UBSAN: shift-out-of-bounds in net/nfc/nci/core.c:912:45
shift exponent 4294967071 is too large for 32-bit type 'int'
CPU: 1 PID: 30237 Comm: syz-executor.2 Not tainted 6.3.0-rc4-next-20230329-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x136/0x150 lib/dump_stack.c:106
ubsan_epilogue lib/ubsan.c:217 [inline]
__ubsan_handle_shift_out_of_bounds+0x221/0x5a0 lib/ubsan.c:387
nci_activate_target.cold+0x1a/0x1f net/nfc/nci/core.c:912
nfc_activate_target+0x1f8/0x4c0 net/nfc/core.c:420
nfc_genl_activate_target+0x1f3/0x290 net/nfc/netlink.c:900
genl_family_rcv_msg_doit.isra.0+0x1e6/0x2d0 net/netlink/genetlink.c:968
genl_family_rcv_msg net/netlink/genetlink.c:1048 [inline]
genl_rcv_msg+0x4ff/0x7e0 net/netlink/genetlink.c:1065
netlink_rcv_skb+0x165/0x440 net/netlink/af_netlink.c:2572
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1076
netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline]
netlink_unicast+0x547/0x7f0 net/netlink/af_netlink.c:1365
netlink_sendmsg+0x925/0xe30 net/netlink/af_netlink.c:1942
sock_sendmsg_nosec net/socket.c:724 [inline]
sock_sendmsg+0xde/0x190 net/socket.c:747
____sys_sendmsg+0x71c/0x900 net/socket.c:2501
___sys_sendmsg+0x110/0x1b0 net/socket.c:2555
__sys_sendmsg+0xf7/0x1c0 net/socket.c:2584
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fc4abc8c0f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 90 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc4aca02168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fc4abdabf80 RCX: 00007fc4abc8c0f9
RDX: 0000000000000000 RSI: 0000000020000780 RDI: 0000000000000005
RBP: 00007fc4abce7b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffcb707727f R14: 00007fc4aca02300 R15: 0000000000022000
</TASK>
================================================================================
---
This report 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 syzk...@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot
Jul 7, 2023, 6:22:49 AM7/7/23
to anupne...@gmail.com, da...@davemloft.net, edum...@google.com, krzysztof...@linaro.org, ku...@kernel.org, linux-...@vger.kernel.org, linu...@lists.01.org, net...@vger.kernel.org, pab...@redhat.com, syzkall...@googlegroups.com
syzbot has found a reproducer for the following issue on:
HEAD commit: a452483508d7 Merge tag 's390-6.5-2' of git://git.kernel.or..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=161e174aa80000
kernel config: https://syzkaller.appspot.com/x/.config?x=7df0cabaf5becfdc
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12003f4aa80000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/524f562d731e/disk-a4524835.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/253005f05b78/vmlinux-a4524835.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1864a30871e7/bzImage-a4524835.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0839b7...@syzkaller.appspotmail.com
================================================================================
UBSAN: shift-out-of-bounds in net/nfc/nci/core.c:912:45
shift exponent 268435489 is too large for 32-bit type 'int'
CPU: 0 PID: 5028 Comm: syz-executor696 Not tainted 6.4.0-syzkaller-12155-ga452483508d7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
genl_family_rcv_msg net/netlink/genetlink.c:1050 [inline]
genl_rcv_msg+0x4ff/0x7e0 net/netlink/genetlink.c:1067
netlink_rcv_skb+0x165/0x440 net/netlink/af_netlink.c:2549
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1078
sock_sendmsg_nosec net/socket.c:725 [inline]
sock_sendmsg+0xde/0x190 net/socket.c:748
____sys_sendmsg+0x739/0x920 net/socket.c:2494
___sys_sendmsg+0x110/0x1b0 net/socket.c:2548
__sys_sendmsg+0xf7/0x1c0 net/socket.c:2577
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 71 16 00 00 90 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff49876f2e8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007ff4990542a0 RCX: 00007ff498fc3ab9
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
R13: 0000000000000001 R14: 0000000000000000 R15: 00007ff4990542a8
</TASK>
================================================================================
---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
HEAD commit: a452483508d7 Merge tag 's390-6.5-2' of git://git.kernel.or..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=161e174aa80000
kernel config: https://syzkaller.appspot.com/x/.config?x=7df0cabaf5becfdc
dashboard link: https://syzkaller.appspot.com/bug?extid=0839b78e119aae1fec78
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=123fc664a80000
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12003f4aa80000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/524f562d731e/disk-a4524835.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/253005f05b78/vmlinux-a4524835.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1864a30871e7/bzImage-a4524835.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0839b7...@syzkaller.appspotmail.com
================================================================================
UBSAN: shift-out-of-bounds in net/nfc/nci/core.c:912:45
CPU: 0 PID: 5028 Comm: syz-executor696 Not tainted 6.4.0-syzkaller-12155-ga452483508d7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x136/0x150 lib/dump_stack.c:106
ubsan_epilogue lib/ubsan.c:217 [inline]
__ubsan_handle_shift_out_of_bounds+0x221/0x5a0 lib/ubsan.c:387
nci_activate_target.cold+0x1a/0x1f net/nfc/nci/core.c:912
nfc_activate_target+0x1f8/0x4c0 net/nfc/core.c:420
nfc_genl_activate_target+0x1f3/0x290 net/nfc/netlink.c:900
genl_family_rcv_msg_doit.isra.0+0x1e6/0x2d0 net/netlink/genetlink.c:970
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x136/0x150 lib/dump_stack.c:106
ubsan_epilogue lib/ubsan.c:217 [inline]
__ubsan_handle_shift_out_of_bounds+0x221/0x5a0 lib/ubsan.c:387
nci_activate_target.cold+0x1a/0x1f net/nfc/nci/core.c:912
nfc_activate_target+0x1f8/0x4c0 net/nfc/core.c:420
nfc_genl_activate_target+0x1f3/0x290 net/nfc/netlink.c:900
genl_family_rcv_msg net/netlink/genetlink.c:1050 [inline]
genl_rcv_msg+0x4ff/0x7e0 net/netlink/genetlink.c:1067
netlink_rcv_skb+0x165/0x440 net/netlink/af_netlink.c:2549
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1078
netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline]
netlink_unicast+0x547/0x7f0 net/netlink/af_netlink.c:1365
netlink_sendmsg+0x925/0xe30 net/netlink/af_netlink.c:1914
netlink_unicast+0x547/0x7f0 net/netlink/af_netlink.c:1365
sock_sendmsg_nosec net/socket.c:725 [inline]
sock_sendmsg+0xde/0x190 net/socket.c:748
____sys_sendmsg+0x739/0x920 net/socket.c:2494
___sys_sendmsg+0x110/0x1b0 net/socket.c:2548
__sys_sendmsg+0xf7/0x1c0 net/socket.c:2577
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7ff498fc3ab9
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 71 16 00 00 90 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff49876f2e8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007ff4990542a0 RCX: 00007ff498fc3ab9
RDX: 0000000000000000 RSI: 0000000020000780 RDI: 0000000000000005
RBP: 00007ff49901a510 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
R13: 0000000000000001 R14: 0000000000000000 R15: 00007ff4990542a8
</TASK>
================================================================================
---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
Hillf Danton
Jul 7, 2023, 10:55:13 PM7/7/23
to syzbot, linux-...@vger.kernel.org, syzkall...@googlegroups.com
On Fri, 07 Jul 2023 03:22:47 -0700
Check if protocol is valid before use.
#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git a452483508d7
--- x/net/nfc/nci/core.c
+++ y/net/nfc/nci/core.c
@@ -886,6 +886,9 @@ static int nci_activate_target(struct nf
pr_debug("target_idx %d, protocol 0x%x\n", target->idx, protocol);
+ if (protocol == 0 || NFC_PROTO_MAX <= protocol)
+ return -EINVAL;
+
if ((atomic_read(&ndev->state) != NCI_W4_HOST_SELECT) &&
(atomic_read(&ndev->state) != NCI_POLL_ACTIVE)) {
pr_err("there is no available target to activate\n");
--
> HEAD commit: a452483508d7 Merge tag 's390-6.5-2' of git://git.kernel.or..
> git tree: upstream
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12003f4aa80000
> git tree: upstream
Check if protocol is valid before use.
#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git a452483508d7
--- x/net/nfc/nci/core.c
+++ y/net/nfc/nci/core.c
@@ -886,6 +886,9 @@ static int nci_activate_target(struct nf
pr_debug("target_idx %d, protocol 0x%x\n", target->idx, protocol);
+ if (protocol == 0 || NFC_PROTO_MAX <= protocol)
+ return -EINVAL;
+
if ((atomic_read(&ndev->state) != NCI_W4_HOST_SELECT) &&
(atomic_read(&ndev->state) != NCI_POLL_ACTIVE)) {
pr_err("there is no available target to activate\n");
--
syzbot
Jul 7, 2023, 11:29:43 PM7/7/23
to hda...@sina.com, linux-...@vger.kernel.org, syzkall...@googlegroups.com
Hello,
syzbot has tested the proposed patch and the reproducer did not trigger any issue:
Reported-and-tested-by: syzbot+0839b7...@syzkaller.appspotmail.com
Tested on:
commit: a4524835 Merge tag 's390-6.5-2' of git://git.kernel.or..
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1406e26ca80000
Note: testing is done by a robot and is best-effort only.
syzbot has tested the proposed patch and the reproducer did not trigger any issue:
Reported-and-tested-by: syzbot+0839b7...@syzkaller.appspotmail.com
Tested on:
commit: a4524835 Merge tag 's390-6.5-2' of git://git.kernel.or..
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1406e26ca80000
kernel config: https://syzkaller.appspot.com/x/.config?x=7df0cabaf5becfdc
dashboard link: https://syzkaller.appspot.com/bug?extid=0839b78e119aae1fec78
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch: https://syzkaller.appspot.com/x/patch.diff?x=13f3fad2a80000
dashboard link: https://syzkaller.appspot.com/bug?extid=0839b78e119aae1fec78
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
Note: testing is done by a robot and is best-effort only.
syzbot
Jul 8, 2023, 10:49:21 PM7/8/23
to anupne...@gmail.com, bongs...@samsung.com, da...@davemloft.net, edum...@google.com, hda...@sina.com, krzysztof...@linaro.org, ku...@kernel.org, linux-...@vger.kernel.org, linu...@lists.01.org, net...@vger.kernel.org, pab...@redhat.com, syzkall...@googlegroups.com
syzbot has bisected this issue to:
commit e624e6c3e777fb3dfed036b9da4d433aee3608a5
Author: Bongsu Jeon <bongs...@samsung.com>
Date: Wed Jan 27 13:08:28 2021 +0000
nfc: Add a virtual nci device driver
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=12b7b56ca80000
start commit: a452483508d7 Merge tag 's390-6.5-2' of git://git.kernel.or..
git tree: upstream
final oops: https://syzkaller.appspot.com/x/report.txt?x=11b7b56ca80000
console output: https://syzkaller.appspot.com/x/log.txt?x=16b7b56ca80000
Fixes: e624e6c3e777 ("nfc: Add a virtual nci device driver")
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
commit e624e6c3e777fb3dfed036b9da4d433aee3608a5
Author: Bongsu Jeon <bongs...@samsung.com>
Date: Wed Jan 27 13:08:28 2021 +0000
nfc: Add a virtual nci device driver
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=12b7b56ca80000
start commit: a452483508d7 Merge tag 's390-6.5-2' of git://git.kernel.or..
git tree: upstream
final oops: https://syzkaller.appspot.com/x/report.txt?x=11b7b56ca80000
console output: https://syzkaller.appspot.com/x/log.txt?x=16b7b56ca80000
kernel config: https://syzkaller.appspot.com/x/.config?x=7df0cabaf5becfdc
dashboard link: https://syzkaller.appspot.com/bug?extid=0839b78e119aae1fec78
dashboard link: https://syzkaller.appspot.com/bug?extid=0839b78e119aae1fec78
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=123fc664a80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12003f4aa80000
Reported-by: syzbot+0839b7...@syzkaller.appspotmail.com
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12003f4aa80000
Fixes: e624e6c3e777 ("nfc: Add a virtual nci device driver")
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
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