From: Vladimir Zapolskiy <vladimir_zapolskiy@xxxxxxxxxx>
The change protects almost the whole body of u_audio_iso_complete()
function by PCM stream lock, this is mainly sufficient to avoid a race
between USB request completion and stream termination, the change
prevents a possibility of invalid memory access in interrupt context
by memcpy():
Unable to handle kernel paging request at virtual address 00004e80
pgd = c0004000
[00004e80] *pgd=00000000
Internal error: Oops: 817 [#1] PREEMPT SMP ARM
CPU: 0 PID: 3 Comm: ksoftirqd/0 Tainted: G C 3.14.54+ #117
task: da180b80 ti: da192000 task.ti: da192000
PC is at memcpy+0x50/0x330
LR is at 0xcdd92b0e
pc : [<c029ef30>] lr : [<cdd92b0e>] psr: 20000193
sp : da193ce4 ip : dd86ae26 fp : 0000b180
r10: daf81680 r9 : 00000000 r8 : d58a01ea
r7 : 2c0b43e4 r6 : acdfb08b r5 : 01a271cf r4 : 87389377
r3 : 69469782 r2 : 00000020 r1 : daf82fe0 r0 : 00004e80
Flags: nzCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernel
Control: 10c5387d Table: 2b70804a DAC: 00000015
Process ksoftirqd/0 (pid: 3, stack limit = 0xda192238)
Also added a check for potential !runtime condition, commonly it is
done by PCM_RUNTIME_CHECK(substream) in the beginning, however this
does not completely prevent from oopses in u_audio_iso_complete(),
because the proper protection scheme must be implemented in PCM
library functions.
An example of *not fixed* oops due to substream->runtime->*
dereference by snd_pcm_running(substream) from
snd_pcm_period_elapsed(), where substream->runtime is gone while
waiting the substream lock:
Unable to handle kernel paging request at virtual address 6b6b6b6b
pgd = db7e4000
[6b6b6b6b] *pgd=00000000
CPU: 0 PID: 193 Comm: klogd Tainted: G C 3.14.54+ #118
task: db5ac500 ti: db60c000 task.ti: db60c000
PC is at snd_pcm_period_elapsed+0x48/0xd8 [snd_pcm]
LR is at snd_pcm_period_elapsed+0x40/0xd8 [snd_pcm]
pc : [<>] lr : [<>] psr: 60000193
Flags: nZCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment user
Control: 10c5387d Table: 2b7e404a DAC: 00000015
Process klogd (pid: 193, stack limit = 0xdb60c238)
[<>] (snd_pcm_period_elapsed [snd_pcm]) from [<>] (udc_irq+0x500/0xbbc)
[<>] (udc_irq) from [<>] (ci_irq+0x280/0x304)
[<>] (ci_irq) from [<>] (handle_irq_event_percpu+0xa4/0x40c)
[<>] (handle_irq_event_percpu) from [<>] (handle_irq_event+0x3c/0x5c)
[<>] (handle_irq_event) from [<>] (handle_fasteoi_irq+0xc4/0x110)
[<>] (handle_fasteoi_irq) from [<>] (generic_handle_irq+0x20/0x30)
[<>] (generic_handle_irq) from [<>] (handle_IRQ+0x80/0xc0)
[<>] (handle_IRQ) from [<>] (gic_handle_irq+0x3c/0x60)
[<>] (gic_handle_irq) from [<>] (__irq_svc+0x44/0x78)
Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@xxxxxxxxxx>
[erosca: W/o this patch, with minimal instrumentation [1], I can
consistently reproduce BUG: KASAN: use-after-free [2]]
[1] Instrumentation to reproduce issue [2]:
diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
index a72295c953bb..bd0b308024fe 100644
--- a/drivers/usb/gadget/function/u_audio.c
+++ b/drivers/usb/gadget/function/u_audio.c
@@ -16,6 +16,7 @@
#include <sound/core.h>
#include <sound/pcm.h>
#include <sound/pcm_params.h>
+#include <linux/delay.h>
#include "u_audio.h"
@@ -147,6 +148,8 @@ static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
spin_unlock_irqrestore(&prm->lock, flags);
+ udelay(500); //delay here to increase probability of parallel activities
+
/* Pack USB load in ALSA ring buffer */
pending = prm->dma_bytes - hw_ptr;
[2] After applying [1], below BUG occurs on Rcar-H3-Salvator-X board:
==================================================================
BUG: KASAN: use-after-free in u_audio_iso_complete+0x24c/0x520 [u_audio]
Read of size 8 at addr ffff8006cafcc248 by task swapper/0/0
CPU: 0 PID: 0 Comm: swapper/0 Tainted: G WC 4.14.47+ #160
Hardware name: Renesas Salvator-X board based on r8a7795 ES2.0+ (DT)
Call trace:
[<ffff2000080925ac>] dump_backtrace+0x0/0x364
[<ffff200008092924>] show_stack+0x14/0x1c
[<ffff200008f8dbcc>] dump_stack+0x108/0x174
[<ffff2000083c71b8>] print_address_description+0x7c/0x32c
[<ffff2000083c78e8>] kasan_report+0x324/0x354
[<ffff2000083c6114>] __asan_load8+0x24/0x94
[<ffff2000021d1b34>] u_audio_iso_complete+0x24c/0x520 [u_audio]
[<ffff20000152fe50>] usb_gadget_giveback_request+0x480/0x4d0 [udc_core]
[<ffff200001860ab8>] usbhsg_queue_done+0x100/0x130 [renesas_usbhs]
[<ffff20000185f814>] usbhsf_pkt_handler+0x1a4/0x298 [renesas_usbhs]
[<ffff20000185fb38>] usbhsf_irq_ready+0x128/0x178 [renesas_usbhs]
[<ffff200001859cc8>] usbhs_interrupt+0x440/0x490 [renesas_usbhs]
[<ffff2000081a0288>] __handle_irq_event_percpu+0x594/0xa58
[<ffff2000081a07d0>] handle_irq_event_percpu+0x84/0x12c
[<ffff2000081a0928>] handle_irq_event+0xb0/0x10c
[<ffff2000081a8384>] handle_fasteoi_irq+0x1e0/0x2ec
[<ffff20000819e5f8>] generic_handle_irq+0x2c/0x44
[<ffff20000819f0d0>] __handle_domain_irq+0x190/0x194
[<ffff20000808177c>] gic_handle_irq+0x80/0xac
Exception stack(0xffff200009e97c80 to 0xffff200009e97dc0)
7c80: 0000000000000000 0000000000000000 0000000000000003 ffff200008179298
7ca0: ffff20000ae1c180 dfff200000000000 0000000000000000 ffff2000081f9a88
7cc0: ffff200009eb5960 ffff200009e97cf0 0000000000001600 ffff0400041b064b
7ce0: 0000000000000000 0000000000000002 0000000200000001 0000000000000001
7d00: ffff20000842197c 0000ffff958c4970 0000000000000000 ffff8006da0d5b80
7d20: ffff8006d4678498 0000000000000000 000000126bde0a8b ffff8006d4678480
7d40: 0000000000000000 000000126bdbea64 ffff200008fd0000 ffff8006fffff980
7d60: 00000000495f0018 ffff200009e97dc0 ffff200008b6c4ec ffff200009e97dc0
7d80: ffff200008b6c4f0 0000000020000145 ffff8006da0d5b80 ffff8006d4678498
7da0: ffffffffffffffff ffff8006d4678498 ffff200009e97dc0 ffff200008b6c4f0
[<ffff200008084034>] el1_irq+0xb4/0x12c
[<ffff200008b6c4f0>] cpuidle_enter_state+0x818/0x844
[<ffff200008b6c59c>] cpuidle_enter+0x18/0x20
[<ffff20000815f2e4>] call_cpuidle+0x98/0x9c
[<ffff20000815f674>] do_idle+0x214/0x264
[<ffff20000815facc>] cpu_startup_entry+0x20/0x24
[<ffff200008fb09d8>] rest_init+0x30c/0x320
[<ffff2000095f1338>] start_kernel+0x570/0x5b0
---<-snip->---
Fixes: 132fcb460839 ("usb: gadget: Add Audio Class 2.0 Driver")
Signed-off-by: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx>
---
drivers/usb/gadget/function/u_audio.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
index 8a63009b7cd5..fb5ed97572e5 100644
--- a/drivers/usb/gadget/function/u_audio.c
+++ b/drivers/usb/gadget/function/u_audio.c
@@ -79,7 +79,7 @@ static const struct snd_pcm_hardware uac_pcm_hardware = {
static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
{
unsigned pending;
- unsigned long flags;
+ unsigned long flags, flags2;
unsigned int hw_ptr;
int status = req->status;
struct uac_req *ur = req->context;
@@ -106,7 +106,14 @@ static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
if (!substream)
goto exit;
+ snd_pcm_stream_lock_irqsave(substream, flags2);
+
runtime = substream->runtime;
+ if (!runtime || !snd_pcm_running(substream)) {
+ snd_pcm_stream_unlock_irqrestore(substream, flags2);
+ goto exit;
+ }
+
spin_lock_irqsave(&prm->lock, flags);
if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
@@ -165,6 +172,7 @@ static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
prm->hw_ptr = (hw_ptr + req->actual) % runtime->dma_bytes;
hw_ptr = prm->hw_ptr;
spin_unlock_irqrestore(&prm->lock, flags);
+ snd_pcm_stream_unlock_irqrestore(substream, flags2);
if ((hw_ptr % snd_pcm_lib_period_bytes(substream)) < req->actual)
snd_pcm_period_elapsed(substream);
--
2.17.0
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