[syzbot] [sound?] KMSAN: uninit-value in line6_midibuf_read

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2c9b3512402e Merge tag 'for-linus' of git://git.kernel.org..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=13b02fe9980000
kernel config: https://syzkaller.appspot.com/x/.config?x=6bfb33a8ad10458f
dashboard link: https://syzkaller.appspot.com/bug?extid=78eccfb8b3c9a85fc6c5
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14ee34ad980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1157b8ad980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f8543636ba6c/disk-2c9b3512.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/403c612b7ac5/vmlinux-2c9b3512.xz
kernel image: https://storage.googleapis.com/syzbot-assets/88dc686d170a/bzImage-2c9b3512.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+78eccf...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in line6_midibuf_read+0x76b/0x1050 sound/usb/line6/midibuf.c:185
line6_midibuf_read+0x76b/0x1050 sound/usb/line6/midibuf.c:185
line6_data_received+0x4be/0x7e0 sound/usb/line6/driver.c:306
__usb_hcd_giveback_urb+0x572/0x840 drivers/usb/core/hcd.c:1650
usb_hcd_giveback_urb+0x157/0x720 drivers/usb/core/hcd.c:1734
dummy_timer+0xd3f/0x6aa0 drivers/usb/gadget/udc/dummy_hcd.c:1987
__run_hrtimer kernel/time/hrtimer.c:1689 [inline]
__hrtimer_run_queues+0x564/0xe40 kernel/time/hrtimer.c:1753
hrtimer_interrupt+0x3ab/0x1490 kernel/time/hrtimer.c:1815
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1032 [inline]
__sysvec_apic_timer_interrupt+0xa6/0x3a0 arch/x86/kernel/apic/apic.c:1049
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
sysvec_apic_timer_interrupt+0x7e/0x90 arch/x86/kernel/apic/apic.c:1043
asm_sysvec_apic_timer_interrupt+0x1f/0x30 arch/x86/include/asm/idtentry.h:702
__preempt_count_dec_and_test arch/x86/include/asm/preempt.h:94 [inline]
rcu_read_unlock_sched include/linux/rcupdate.h:954 [inline]
pfn_valid include/linux/mmzone.h:2032 [inline]
kmsan_virt_addr_valid arch/x86/include/asm/kmsan.h:94 [inline]
virt_to_page_or_null+0xf2/0x150 mm/kmsan/shadow.c:75
kmsan_get_metadata+0x146/0x1d0 mm/kmsan/shadow.c:143
kmsan_get_shadow_origin_ptr+0x4d/0xb0 mm/kmsan/shadow.c:102
get_shadow_origin_ptr mm/kmsan/instrumentation.c:36 [inline]
__msan_metadata_ptr_for_load_8+0x24/0x40 mm/kmsan/instrumentation.c:92
on_stack+0x57/0x1b0
update_stack_state+0xc1/0x270 arch/x86/kernel/unwind_frame.c:228
unwind_next_frame+0x19a/0x470 arch/x86/kernel/unwind_frame.c:315
arch_stack_walk+0x1ec/0x2d0 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0xaa/0xe0 kernel/stacktrace.c:122
kmsan_save_stack_with_flags mm/kmsan/core.c:74 [inline]
kmsan_internal_chain_origin+0x57/0xd0 mm/kmsan/core.c:183
__msan_chain_origin+0xc3/0x150 mm/kmsan/instrumentation.c:251
skb_clone+0x460/0x550 net/core/skbuff.c:2066
__tcp_transmit_skb+0x433/0x4880 net/ipv4/tcp_output.c:1312
tcp_transmit_skb net/ipv4/tcp_output.c:1484 [inline]
tcp_write_xmit+0x3a3d/0x8f00 net/ipv4/tcp_output.c:2829
__tcp_push_pending_frames+0xc4/0x380 net/ipv4/tcp_output.c:3014
tcp_push+0x755/0x7a0 net/ipv4/tcp.c:747
tcp_sendmsg_locked+0x619d/0x6e20 net/ipv4/tcp.c:1322
tcp_sendmsg+0x49/0x90 net/ipv4/tcp.c:1354
inet_sendmsg+0x142/0x280 net/ipv4/af_inet.c:853
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0x267/0x380 net/socket.c:745
sock_write_iter+0x368/0x3d0 net/socket.c:1160
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0xb2f/0x1550 fs/read_write.c:590
ksys_write+0x20f/0x4c0 fs/read_write.c:643
__do_sys_write fs/read_write.c:655 [inline]
__se_sys_write fs/read_write.c:652 [inline]
__x64_sys_write+0x93/0xe0 fs/read_write.c:652
x64_sys_call+0x3490/0x3c10 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
slab_post_alloc_hook mm/slub.c:3985 [inline]
slab_alloc_node mm/slub.c:4028 [inline]
__do_kmalloc_node mm/slub.c:4148 [inline]
__kmalloc_noprof+0x661/0xf30 mm/slub.c:4161
kmalloc_noprof include/linux/slab.h:685 [inline]
line6_midibuf_init+0x43/0x180 sound/usb/line6/midibuf.c:51
line6_init_midi+0x3e7/0x670 sound/usb/line6/midi.c:284
line6_init_cap_control+0x54e/0x770 sound/usb/line6/driver.c:704
line6_probe+0xeae/0x1120 sound/usb/line6/driver.c:797
pod_probe+0x79/0x90 sound/usb/line6/pod.c:522
usb_probe_interface+0xd6f/0x1350 drivers/usb/core/driver.c:399
really_probe+0x4db/0xd90 drivers/base/dd.c:656
__driver_probe_device+0x2ab/0x5d0 drivers/base/dd.c:798
driver_probe_device+0x72/0x890 drivers/base/dd.c:828
__device_attach_driver+0x568/0x9e0 drivers/base/dd.c:956
bus_for_each_drv+0x403/0x620 drivers/base/bus.c:457
__device_attach+0x3c1/0x650 drivers/base/dd.c:1028
device_initial_probe+0x32/0x40 drivers/base/dd.c:1077
bus_probe_device+0x3dc/0x5c0 drivers/base/bus.c:532
device_add+0x13aa/0x1ba0 drivers/base/core.c:3679
usb_set_configuration+0x31c9/0x38d0 drivers/usb/core/message.c:2210
usb_generic_driver_probe+0x109/0x2a0 drivers/usb/core/generic.c:254
usb_probe_device+0x3a7/0x690 drivers/usb/core/driver.c:294
really_probe+0x4db/0xd90 drivers/base/dd.c:656
__driver_probe_device+0x2ab/0x5d0 drivers/base/dd.c:798
driver_probe_device+0x72/0x890 drivers/base/dd.c:828
__device_attach_driver+0x568/0x9e0 drivers/base/dd.c:956
bus_for_each_drv+0x403/0x620 drivers/base/bus.c:457
__device_attach+0x3c1/0x650 drivers/base/dd.c:1028
device_initial_probe+0x32/0x40 drivers/base/dd.c:1077
bus_probe_device+0x3dc/0x5c0 drivers/base/bus.c:532
device_add+0x13aa/0x1ba0 drivers/base/core.c:3679
usb_new_device+0x15f4/0x2470 drivers/usb/core/hub.c:2651
hub_port_connect drivers/usb/core/hub.c:5521 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5661 [inline]
port_event drivers/usb/core/hub.c:5821 [inline]
hub_event+0x4ff8/0x72d0 drivers/usb/core/hub.c:5903
process_one_work kernel/workqueue.c:3231 [inline]
process_scheduled_works+0xae0/0x1c40 kernel/workqueue.c:3312
worker_thread+0xea5/0x1520 kernel/workqueue.c:3390
kthread+0x3e2/0x540 kernel/kthread.c:389
ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

CPU: 0 PID: 5052 Comm: sshd Not tainted 6.10.0-syzkaller-11185-g2c9b3512402e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
=====================================================


---
This report is generated by a bot. It may contain errors.
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syzbot engineers can be reached at syzk...@googlegroups.com.

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#syz test: git://repo/address.git branch-or-commit-hash
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[Edward Adam Davis]

when alloc buffer for midi_buffer->buf, init mem to 0

#syz test: upstream 2c9b3512402e

diff --git a/sound/usb/line6/midibuf.c b/sound/usb/line6/midibuf.c
index e7f830f7526c..1b699cb3b38d 100644
--- a/sound/usb/line6/midibuf.c
+++ b/sound/usb/line6/midibuf.c
@@ -48,7 +48,7 @@ void line6_midibuf_reset(struct midi_buffer *this)

int line6_midibuf_init(struct midi_buffer *this, int size, int split)
{
- this->buf = kmalloc(size, GFP_KERNEL);
+ this->buf = kzalloc(size, GFP_KERNEL);

if (this->buf == NULL)
return -ENOMEM;

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+78eccf...@syzkaller.appspotmail.com
Tested-by: syzbot+78eccf...@syzkaller.appspotmail.com

Tested on:

commit: 2c9b3512 Merge tag 'for-linus' of git://git.kernel.org..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1481653d980000

kernel config: https://syzkaller.appspot.com/x/.config?x=6bfb33a8ad10458f
dashboard link: https://syzkaller.appspot.com/bug?extid=78eccfb8b3c9a85fc6c5
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=133b2af1980000

Note: testing is done by a robot and is best-effort only.

[Edward Adam Davis]

Syzbot report KMSAN uninit-value warnings.
When alloc buffer for midi_buffer->buf, init mem to 0.

Reported-and-tested-by: syzbot+78eccf...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=78eccfb8b3c9a85fc6c5
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
sound/usb/line6/midibuf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/line6/midibuf.c b/sound/usb/line6/midibuf.c
index e7f830f7526c..1b699cb3b38d 100644
--- a/sound/usb/line6/midibuf.c
+++ b/sound/usb/line6/midibuf.c
@@ -48,7 +48,7 @@ void line6_midibuf_reset(struct midi_buffer *this)

int line6_midibuf_init(struct midi_buffer *this, int size, int split)
{
- this->buf = kmalloc(size, GFP_KERNEL);
+ this->buf = kzalloc(size, GFP_KERNEL);

if (this->buf == NULL)
return -ENOMEM;

--
2.43.0

[Takashi Iwai]

Thanks for the patch. But this just hides the KMSAN warning, and it
doesn't really address the cause - why it was exposed at all; the
driver code had already a check and should have accessed only the
updated data, but by some reason it slipped.

Through a quick glance, I see a possible. If that's the cause, the
patch like below might help. I checked the reproducer locally but
couldn't trigger the bug on my image, unfortunately, so it's just a
wild guess, and it might be shooting a wrong way. Let's see.


thanks,

Takashi

-- 8< --
--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -286,12 +286,14 @@ static void line6_data_received(struct urb *urb)
{
struct usb_line6 *line6 = (struct usb_line6 *)urb->context;
struct midi_buffer *mb = &line6->line6midi->midibuf_in;
+ unsigned long flags;
int done;

if (urb->status == -ESHUTDOWN)
return;

if (line6->properties->capabilities & LINE6_CAP_CONTROL_MIDI) {
+ spin_lock_irqsave(&line6->line6midi->lock, flags);
done =
line6_midibuf_write(mb, urb->transfer_buffer, urb->actual_length);

@@ -300,12 +302,15 @@ static void line6_data_received(struct urb *urb)
dev_dbg(line6->ifcdev, "%d %d buffer overflow - message skipped\n",
done, urb->actual_length);
}
+ spin_unlock_irqrestore(&line6->line6midi->lock, flags);

for (;;) {
+ spin_lock_irqsave(&line6->line6midi->lock, flags);
done =
line6_midibuf_read(mb, line6->buffer_message,
LINE6_MIDI_MESSAGE_MAXLEN,
LINE6_MIDIBUF_READ_RX);
+ spin_unlock_irqrestore(&line6->line6midi->lock, flags);

if (done <= 0)
break;