Re: [syzbot] KASAN: use-after-free Read in __snd_rawmidi_transmit_peek

Re: [syzbot] KASAN: use-after-free Read in __snd_rawmidi_transmit_peek

[syzbot]

Hello,

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

Reported-and-tested-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com

Tested on:

commit:         a1994480 Merge tag 'hardening-v5.18-rc3' of git://git...
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
kernel config:  https://syzkaller.appspot.com/x/.config?x=eb177500e563582f
dashboard link: https://syzkaller.appspot.com/bug?extid=70e777a39907d6d5fd0a
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=1096d994f00000

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

Re: [syzbot] KASAN: use-after-free Read in __snd_rawmidi_transmit_peek

[Takashi Iwai]

On Tue, 19 Apr 2022 11:01:47 +0200,
Takashi Iwai wrote:
> 
> On Mon, 18 Apr 2022 12:12:23 +0200,
> syzbot wrote:
> > 
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    a19944809fe9 Merge tag 'hardening-v5.18-rc3' of git://git...
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=16a40ae0f00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=eb177500e563582f
> > dashboard link: https://syzkaller.appspot.com/bug?extid=70e777a39907d6d5fd0a
> > 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=1590dfa8f00000
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com
> > 
> > ==================================================================
> > BUG: KASAN: use-after-free in __snd_rawmidi_transmit_peek+0x261/0x360 sound/core/rawmidi.c:1286
> 
> Looks like a leftover work.  The fix patch is below.

On the second thought, this would be rather in a different code path,
and the fix should be smaller like below.  Let's see.


Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: usb-audio: Clear MIDI port active flag after draining

When a rawmidi output stream is closed, it calls the drain at first,
then does trigger-off only when the drain returns -ERESTARTSYS as a
fallback.  It implies that each driver should turn off the stream
properly after the drain.  Meanwhile, USB-audio MIDI interface didn't
change the port->active flag after the drain.  This may leave the
output work picking up the port that is closed right now, which
eventually leads to a use-after-free for the already released rawmidi
object.

This patch fixes the bug by properly clearing the port->active flag
after the output drain.

Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/00000000000011555605dceaff03@google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/usb/midi.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index 2c01649c70f6..7c6ca2b433a5 100644
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1194,6 +1194,7 @@ static void snd_usbmidi_output_drain(struct snd_rawmidi_substream *substream)
 		} while (drain_urbs && timeout);
 		finish_wait(&ep->drain_wait, &wait);
 	}
+	port->active = 0;
 	spin_unlock_irq(&ep->buffer_lock);
 }
 
-- 
2.34.1

Re: [syzbot] KASAN: use-after-free Read in __snd_rawmidi_transmit_peek

[Takashi Iwai]

On Tue, 19 Apr 2022 11:01:47 +0200,
Takashi Iwai wrote:
> 
> On Mon, 18 Apr 2022 12:12:23 +0200,
> syzbot wrote:
> > 
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    a19944809fe9 Merge tag 'hardening-v5.18-rc3' of git://git...
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=16a40ae0f00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=eb177500e563582f
> > dashboard link: https://syzkaller.appspot.com/bug?extid=70e777a39907d6d5fd0a
> > 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=1590dfa8f00000
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com
> > 
> > ==================================================================
> > BUG: KASAN: use-after-free in __snd_rawmidi_transmit_peek+0x261/0x360 sound/core/rawmidi.c:1286
> 
> Looks like a leftover work.  The fix patch is below.

On the second thought, this would be rather in a different code path,
and the fix should be smaller like below.  Let's see.


Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: usb-audio: Clear MIDI port active flag after draining

When a rawmidi output stream is closed, it calls the drain at first,
then does trigger-off only when the drain returns -ERESTARTSYS as a
fallback.  It implies that each driver should turn off the stream
properly after the drain.  Meanwhile, USB-audio MIDI interface didn't
change the port->active flag after the drain.  This may leave the
output work picking up the port that is closed right now, which
eventually leads to a use-after-free for the already released rawmidi
object.

This patch fixes the bug by properly clearing the port->active flag
after the output drain.

Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/00000000000011555605dceaff03@google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/usb/midi.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index 2c01649c70f6..7c6ca2b433a5 100644
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1194,6 +1194,7 @@ static void snd_usbmidi_output_drain(struct snd_rawmidi_substream *substream)
 		} while (drain_urbs && timeout);
 		finish_wait(&ep->drain_wait, &wait);
 	}
+	port->active = 0;
 	spin_unlock_irq(&ep->buffer_lock);
 }
 
-- 
2.34.1

Re: [syzbot] KASAN: use-after-free Read in __snd_rawmidi_transmit_peek

[Takashi Iwai]

On Mon, 18 Apr 2022 12:12:23 +0200,
syzbot wrote:
> 
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    a19944809fe9 Merge tag 'hardening-v5.18-rc3' of git://git...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16a40ae0f00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=eb177500e563582f
> dashboard link: https://syzkaller.appspot.com/bug?extid=70e777a39907d6d5fd0a
> 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=1590dfa8f00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in __snd_rawmidi_transmit_peek+0x261/0x360 sound/core/rawmidi.c:1286

Looks like a leftover work.  The fix patch is below.


Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: usb-audio: Fix potential use-after-free at releasing
 MIDI streams

As recently spotted by syzbot, the USB MIDI code may leave a work that
handles the pending output queue even after a stream gets released
(either internally via sequencer or via device files), which may lead
to use-after-free.  We have already a proper drop of pending URBs but
this is executed only at the device disconnection.

This patch moves the URB clean-up code into both the code path that is
called at releasing, namely, snd_usb_midi_in_endpoint_delete() and
snd_usb_midi_out_endpoint_clear() functions, so that the pending URBs
and work are cleared properly before releasing the resources.

Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/00000000000011555605dceaff03@google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/usb/midi.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index 2c01649c70f6..8e5281f7f1fc 100644
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1247,6 +1247,10 @@ static void snd_usbmidi_in_endpoint_delete(struct snd_usb_midi_in_endpoint *ep)
 {
 	unsigned int i;
 
+	for (i = 0; i < INPUT_URBS; ++i)
+		if (ep->urbs[i])
+			usb_kill_urb(ep->urbs[i]);
+
 	for (i = 0; i < INPUT_URBS; ++i)
 		if (ep->urbs[i])
 			free_urb_and_buffer(ep->umidi, ep->urbs[i],
@@ -1327,6 +1331,18 @@ static void snd_usbmidi_out_endpoint_clear(struct snd_usb_midi_out_endpoint *ep)
 {
 	unsigned int i;
 
+	cancel_work_sync(&ep->work);
+	for (i = 0; i < OUTPUT_URBS; ++i)
+		if (ep->urbs[i].urb)
+			usb_kill_urb(ep->urbs[i].urb);
+	if (ep->umidi->usb_protocol_ops->finish_out_endpoint)
+		ep->umidi->usb_protocol_ops->finish_out_endpoint(ep);
+	ep->active_urbs = 0;
+	if (ep->drain_urbs) {
+		ep->drain_urbs = 0;
+		wake_up(&ep->drain_wait);
+	}
+
 	for (i = 0; i < OUTPUT_URBS; ++i)
 		if (ep->urbs[i].urb) {
 			free_urb_and_buffer(ep->umidi, ep->urbs[i].urb,
@@ -1469,7 +1485,7 @@ static void snd_usbmidi_free(struct snd_usb_midi *umidi)
 void snd_usbmidi_disconnect(struct list_head *p)
 {
 	struct snd_usb_midi *umidi;
-	unsigned int i, j;
+	unsigned int i;
 
 	umidi = list_entry(p, struct snd_usb_midi, list);
 	/*
@@ -1487,22 +1503,6 @@ void snd_usbmidi_disconnect(struct list_head *p)
 
 	for (i = 0; i < MIDI_MAX_ENDPOINTS; ++i) {
 		struct snd_usb_midi_endpoint *ep = &umidi->endpoints[i];
-		if (ep->out)
-			cancel_work_sync(&ep->out->work);
-		if (ep->out) {
-			for (j = 0; j < OUTPUT_URBS; ++j)
-				usb_kill_urb(ep->out->urbs[j].urb);
-			if (umidi->usb_protocol_ops->finish_out_endpoint)
-				umidi->usb_protocol_ops->finish_out_endpoint(ep->out);
-			ep->out->active_urbs = 0;
-			if (ep->out->drain_urbs) {
-				ep->out->drain_urbs = 0;
-				wake_up(&ep->out->drain_wait);
-			}
-		}
-		if (ep->in)
-			for (j = 0; j < INPUT_URBS; ++j)
-				usb_kill_urb(ep->in->urbs[j]);
 		/* free endpoints here; later call can result in Oops */
 		if (ep->out)
 			snd_usbmidi_out_endpoint_clear(ep->out);
-- 
2.31.1

Re: [syzbot] KASAN: use-after-free Read in __snd_rawmidi_transmit_peek

[Takashi Iwai]

On Mon, 18 Apr 2022 12:12:23 +0200,
syzbot wrote:
> 
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    a19944809fe9 Merge tag 'hardening-v5.18-rc3' of git://git...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16a40ae0f00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=eb177500e563582f
> dashboard link: https://syzkaller.appspot.com/bug?extid=70e777a39907d6d5fd0a
> 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=1590dfa8f00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in __snd_rawmidi_transmit_peek+0x261/0x360 sound/core/rawmidi.c:1286

Looks like a leftover work.  The fix patch is below.


Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: usb-audio: Fix potential use-after-free at releasing
 MIDI streams

As recently spotted by syzbot, the USB MIDI code may leave a work that
handles the pending output queue even after a stream gets released
(either internally via sequencer or via device files), which may lead
to use-after-free.  We have already a proper drop of pending URBs but
this is executed only at the device disconnection.

This patch moves the URB clean-up code into both the code path that is
called at releasing, namely, snd_usb_midi_in_endpoint_delete() and
snd_usb_midi_out_endpoint_clear() functions, so that the pending URBs
and work are cleared properly before releasing the resources.

Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/00000000000011555605dceaff03@google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/usb/midi.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index 2c01649c70f6..8e5281f7f1fc 100644
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1247,6 +1247,10 @@ static void snd_usbmidi_in_endpoint_delete(struct snd_usb_midi_in_endpoint *ep)
 {
 	unsigned int i;
 
+	for (i = 0; i < INPUT_URBS; ++i)
+		if (ep->urbs[i])
+			usb_kill_urb(ep->urbs[i]);
+
 	for (i = 0; i < INPUT_URBS; ++i)
 		if (ep->urbs[i])
 			free_urb_and_buffer(ep->umidi, ep->urbs[i],
@@ -1327,6 +1331,18 @@ static void snd_usbmidi_out_endpoint_clear(struct snd_usb_midi_out_endpoint *ep)
 {
 	unsigned int i;
 
+	cancel_work_sync(&ep->work);
+	for (i = 0; i < OUTPUT_URBS; ++i)
+		if (ep->urbs[i].urb)
+			usb_kill_urb(ep->urbs[i].urb);
+	if (ep->umidi->usb_protocol_ops->finish_out_endpoint)
+		ep->umidi->usb_protocol_ops->finish_out_endpoint(ep);
+	ep->active_urbs = 0;
+	if (ep->drain_urbs) {
+		ep->drain_urbs = 0;
+		wake_up(&ep->drain_wait);
+	}
+
 	for (i = 0; i < OUTPUT_URBS; ++i)
 		if (ep->urbs[i].urb) {
 			free_urb_and_buffer(ep->umidi, ep->urbs[i].urb,
@@ -1469,7 +1485,7 @@ static void snd_usbmidi_free(struct snd_usb_midi *umidi)
 void snd_usbmidi_disconnect(struct list_head *p)
 {
 	struct snd_usb_midi *umidi;
-	unsigned int i, j;
+	unsigned int i;
 
 	umidi = list_entry(p, struct snd_usb_midi, list);
 	/*
@@ -1487,22 +1503,6 @@ void snd_usbmidi_disconnect(struct list_head *p)
 
 	for (i = 0; i < MIDI_MAX_ENDPOINTS; ++i) {
 		struct snd_usb_midi_endpoint *ep = &umidi->endpoints[i];
-		if (ep->out)
-			cancel_work_sync(&ep->out->work);
-		if (ep->out) {
-			for (j = 0; j < OUTPUT_URBS; ++j)
-				usb_kill_urb(ep->out->urbs[j].urb);
-			if (umidi->usb_protocol_ops->finish_out_endpoint)
-				umidi->usb_protocol_ops->finish_out_endpoint(ep->out);
-			ep->out->active_urbs = 0;
-			if (ep->out->drain_urbs) {
-				ep->out->drain_urbs = 0;
-				wake_up(&ep->out->drain_wait);
-			}
-		}
-		if (ep->in)
-			for (j = 0; j < INPUT_URBS; ++j)
-				usb_kill_urb(ep->in->urbs[j]);
 		/* free endpoints here; later call can result in Oops */
 		if (ep->out)
 			snd_usbmidi_out_endpoint_clear(ep->out);
-- 
2.31.1

Re: [syzbot] KASAN: use-after-free Read in __snd_rawmidi_transmit_peek

[syzbot]

Hello,

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

Reported-and-tested-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com

Tested on:

commit:         a1994480 Merge tag 'hardening-v5.18-rc3' of git://git...
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
kernel config:  https://syzkaller.appspot.com/x/.config?x=eb177500e563582f
dashboard link: https://syzkaller.appspot.com/bug?extid=70e777a39907d6d5fd0a
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=13d94b3f700000

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

[syzbot] KASAN: use-after-free Read in __snd_rawmidi_transmit_peek

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    a19944809fe9 Merge tag 'hardening-v5.18-rc3' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16a40ae0f00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=eb177500e563582f
dashboard link: https://syzkaller.appspot.com/bug?extid=70e777a39907d6d5fd0a
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=1590dfa8f00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in __snd_rawmidi_transmit_peek+0x261/0x360 sound/core/rawmidi.c:1286
Read of size 1 at addr ffff88807eac2072 by task kworker/1:1H/51

CPU: 1 PID: 51 Comm: kworker/1:1H Not tainted 5.18.0-rc2-syzkaller-00050-ga19944809fe9 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_highpri snd_usbmidi_out_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description.constprop.0.cold+0xeb/0x495 mm/kasan/report.c:313
 print_report mm/kasan/report.c:429 [inline]
 kasan_report.cold+0xf4/0x1c6 mm/kasan/report.c:491
 __snd_rawmidi_transmit_peek+0x261/0x360 sound/core/rawmidi.c:1286
 snd_rawmidi_transmit+0x8d/0xf0 sound/core/rawmidi.c:1411
 snd_usbmidi_standard_output+0x264/0xc10 sound/usb/midi.c:650
 snd_usbmidi_do_output+0x200/0x510 sound/usb/midi.c:311
 process_one_work+0x996/0x1610 kernel/workqueue.c:2289
 worker_thread+0x665/0x1080 kernel/workqueue.c:2436
 kthread+0x2e9/0x3a0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298
 </TASK>

Allocated by task 5812:
 kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:436 [inline]
 ____kasan_kmalloc mm/kasan/common.c:515 [inline]
 ____kasan_kmalloc mm/kasan/common.c:474 [inline]
 __kasan_kmalloc+0xa9/0xd0 mm/kasan/common.c:524
 kmalloc_node include/linux/slab.h:604 [inline]
 kvmalloc_node+0x3e/0x130 mm/util.c:580
 kvmalloc include/linux/slab.h:731 [inline]
 kvzalloc include/linux/slab.h:739 [inline]
 snd_rawmidi_runtime_create sound/core/rawmidi.c:162 [inline]
 open_substream+0x340/0x8b0 sound/core/rawmidi.c:306
 rawmidi_open_priv+0x591/0x6f0 sound/core/rawmidi.c:357
 snd_rawmidi_kernel_open+0x1b5/0x270 sound/core/rawmidi.c:392
 midisynth_use+0xee/0x270 sound/core/seq/seq_midi.c:215
 subscribe_port sound/core/seq/seq_ports.c:412 [inline]
 check_and_subscribe_port+0x89a/0xb80 sound/core/seq/seq_ports.c:495
 snd_seq_port_connect+0x382/0x540 sound/core/seq/seq_ports.c:581
 snd_seq_ioctl_subscribe_port+0x1fc/0x400 sound/core/seq/seq_clientmgr.c:1492
 snd_seq_kernel_client_ctl+0x102/0x1e0 sound/core/seq/seq_clientmgr.c:2369
 snd_seq_oss_midi_open+0x582/0x6e0 sound/core/seq/oss/seq_oss_midi.c:359
 snd_seq_oss_synth_setup_midi+0x12d/0x530 sound/core/seq/oss/seq_oss_synth.c:269
 snd_seq_oss_open+0x8c3/0xa80 sound/core/seq/oss/seq_oss_init.c:260
 odev_open+0x6c/0x90 sound/core/seq/oss/seq_oss.c:128
 soundcore_open+0x44e/0x620 sound/sound_core.c:593
 chrdev_open+0x266/0x770 fs/char_dev.c:414
 do_dentry_open+0x4a1/0x11e0 fs/open.c:824
 do_open fs/namei.c:3476 [inline]
 path_openat+0x1c71/0x2910 fs/namei.c:3609
 do_filp_open+0x1aa/0x400 fs/namei.c:3636
 do_sys_openat2+0x16d/0x4c0 fs/open.c:1213
 do_sys_open fs/open.c:1229 [inline]
 __do_sys_openat fs/open.c:1245 [inline]
 __se_sys_openat fs/open.c:1240 [inline]
 __x64_sys_openat+0x13f/0x1f0 fs/open.c:1240
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 5811:
 kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38
 kasan_set_track+0x21/0x30 mm/kasan/common.c:45
 kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:370
 ____kasan_slab_free mm/kasan/common.c:366 [inline]
 ____kasan_slab_free+0x166/0x1a0 mm/kasan/common.c:328
 kasan_slab_free include/linux/kasan.h:200 [inline]
 slab_free_hook mm/slub.c:1728 [inline]
 slab_free_freelist_hook+0x8b/0x1c0 mm/slub.c:1754
 slab_free mm/slub.c:3510 [inline]
 kfree+0xd6/0x4d0 mm/slub.c:4552
 kvfree+0x42/0x50 mm/util.c:615
 snd_rawmidi_runtime_free sound/core/rawmidi.c:176 [inline]
 close_substream.part.0+0x185/0x720 sound/core/rawmidi.c:528
 close_substream sound/core/rawmidi.c:507 [inline]
 rawmidi_release_priv+0x192/0x270 sound/core/rawmidi.c:547
 snd_rawmidi_kernel_release+0x39/0xd0 sound/core/rawmidi.c:564
 midisynth_unuse+0x45/0x80 sound/core/seq/seq_midi.c:244
 unsubscribe_port sound/core/seq/seq_ports.c:437 [inline]
 __delete_and_unsubscribe_port+0x270/0x4c0 sound/core/seq/seq_ports.c:537
 snd_seq_port_disconnect+0x41c/0x5d0 sound/core/seq/seq_ports.c:616
 snd_seq_ioctl_unsubscribe_port+0x1fc/0x400 sound/core/seq/seq_clientmgr.c:1537
 snd_seq_kernel_client_ctl+0x102/0x1e0 sound/core/seq/seq_clientmgr.c:2369
 snd_seq_oss_midi_close+0x44f/0x4d0 sound/core/seq/oss/seq_oss_midi.c:404
 snd_seq_oss_synth_reset+0x422/0x880 sound/core/seq/oss/seq_oss_synth.c:406
 snd_seq_oss_reset+0x6f/0x290 sound/core/seq/oss/seq_oss_init.c:435
 snd_seq_oss_release+0x78/0x1a0 sound/core/seq/oss/seq_oss_init.c:412
 odev_release+0x4f/0x70 sound/core/seq/oss/seq_oss.c:144
 __fput+0x277/0x9d0 fs/file_table.c:317
 task_work_run+0xdd/0x1a0 kernel/task_work.c:164
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:169 [inline]
 exit_to_user_mode_prepare+0x23c/0x250 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
 syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:294
 do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff88807eac2000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 114 bytes inside of
 4096-byte region [ffff88807eac2000, ffff88807eac3000)

The buggy address belongs to the physical page:
page:ffffea0001fab000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7eac0
head:ffffea0001fab000 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 ffffea0001d2a000 dead000000000002 ffff888010c42140
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 3703, tgid 3703 (syz-executor.4), ts 1615766892626, free_ts 34515408626
 prep_new_page mm/page_alloc.c:2441 [inline]
 get_page_from_freelist+0xba2/0x3e00 mm/page_alloc.c:4182
 __alloc_pages+0x1b2/0x500 mm/page_alloc.c:5408
 alloc_pages+0x1aa/0x310 mm/mempolicy.c:2272
 alloc_slab_page mm/slub.c:1799 [inline]
 allocate_slab+0x26c/0x3c0 mm/slub.c:1944
 new_slab mm/slub.c:2004 [inline]
 ___slab_alloc+0x8df/0xf20 mm/slub.c:3005
 __slab_alloc.constprop.0+0x4d/0xa0 mm/slub.c:3092
 slab_alloc_node mm/slub.c:3183 [inline]
 slab_alloc mm/slub.c:3225 [inline]
 kmem_cache_alloc_trace+0x310/0x3f0 mm/slub.c:3256
 kmalloc include/linux/slab.h:581 [inline]
 kzalloc include/linux/slab.h:714 [inline]
 kobject_uevent_env+0x235/0x1660 lib/kobject_uevent.c:524
 device_add+0xb20/0x1e20 drivers/base/core.c:3386
 netdev_register_kobject+0x181/0x430 net/core/net-sysfs.c:2008
 register_netdevice+0xd9d/0x15b0 net/core/dev.c:9961
 __rtnl_newlink+0x1555/0x1760 net/core/rtnetlink.c:3485
 rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3531
 rtnetlink_rcv_msg+0x413/0xb80 net/core/rtnetlink.c:5990
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2496
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1356 [inline]
 free_pcp_prepare+0x549/0xd20 mm/page_alloc.c:1406
 free_unref_page_prepare mm/page_alloc.c:3328 [inline]
 free_unref_page+0x19/0x6a0 mm/page_alloc.c:3423
 qlink_free mm/kasan/quarantine.c:157 [inline]
 qlist_free_all+0x6a/0x170 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x180/0x200 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0xa2/0xc0 mm/kasan/common.c:446
 kasan_slab_alloc include/linux/kasan.h:224 [inline]
 slab_post_alloc_hook mm/slab.h:749 [inline]
 slab_alloc_node mm/slub.c:3217 [inline]
 kmem_cache_alloc_node+0x255/0x3f0 mm/slub.c:3267
 __alloc_skb+0x215/0x340 net/core/skbuff.c:414
 alloc_skb include/linux/skbuff.h:1300 [inline]
 alloc_skb_with_frags+0x93/0x730 net/core/skbuff.c:5995
 sock_alloc_send_pskb+0x793/0x920 net/core/sock.c:2600
 unix_dgram_sendmsg+0x414/0x1a90 net/unix/af_unix.c:1896
 sock_sendmsg_nosec net/socket.c:705 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:725
 __sys_sendto+0x216/0x310 net/socket.c:2040
 __do_sys_sendto net/socket.c:2052 [inline]
 __se_sys_sendto net/socket.c:2048 [inline]
 __x64_sys_sendto+0xdd/0x1b0 net/socket.c:2048
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Memory state around the buggy address:
 ffff88807eac1f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88807eac1f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88807eac2000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                             ^
 ffff88807eac2080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807eac2100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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