| Message ID | 20191105233652.21033-1-tranmanphong@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | usb: appledisplay: fix use-after-free in bl_get_brightness | expand |
Am Mittwoch, den 06.11.2019, 06:36 +0700 schrieb Phong Tran: > In context of USB disconnect, the delaywork trigger and calling > appledisplay_bl_get_brightness() and the msgdata was freed. > > add the checking return value of usb_control_msg() and only update the > data while the retval is valid. Hi, I am afraid there are some issues with your patch. First, let me stress that you found the right place to fix an issue and you partially fixed an issue. But the the fix you applied is incomplete and left another issue open. Your patch still allows doing IO to a device that may already be bound to another driver. That is bad, especially as the buffer is already free. Yes, if IO is failing, you have fixed that narrow issue. But it need not fail. If you look into appledisplay_probe() you will see that it can fail because backlight_device_register() fails. The error handling will thereupon kill the URB and free memory. But it will not kill an already scheduled work. The scheduled work will then call usb_control_msg() on pdata->msgdata, which has been freed. If that IO fails, all is well. If not, the issue still exists. Secondly, your error check is off by 2. You are checking only for usb_control_msg() failing. But it can return only one byte instead of two. If that happens, the value you return is stale, although the buffer is correctly allocated. Regards Oliver The correct fix for both issues would be: #syz test: https://github.com/google/kasan.git e0bd8d79 From 2497a62bdbeb9bd94f690c22d96dd1b8cf22861f Mon Sep 17 00:00:00 2001 From: Oliver Neukum <oneukum@suse.com> Date: Wed, 6 Nov 2019 12:36:28 +0100 Subject: [PATCH] appledisplay: fix error handling in the scheduled work The work item can operate on 1. stale memory left over from the last transfer the actual length of the data transfered needs to be checked 2. memory already freed the error handling in appledisplay_probe() needs to cancel the work in that case Signed-off-by: Oliver Neukum <oneukum@suse.com> --- drivers/usb/misc/appledisplay.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c index ac92725458b5..ba1eaabc7796 100644 --- a/drivers/usb/misc/appledisplay.c +++ b/drivers/usb/misc/appledisplay.c @@ -164,7 +164,12 @@ static int appledisplay_bl_get_brightness(struct backlight_device *bd) 0, pdata->msgdata, 2, ACD_USB_TIMEOUT); - brightness = pdata->msgdata[1]; + if (retval < 2) { + if (retval >= 0) + retval = -EMSGSIZE; + } else { + brightness = pdata->msgdata[1]; + } mutex_unlock(&pdata->sysfslock); if (retval < 0) @@ -299,6 +304,7 @@ static int appledisplay_probe(struct usb_interface *iface, if (pdata) { if (pdata->urb) { usb_kill_urb(pdata->urb); + cancel_delayed_work_sync(&pdata->work); if (pdata->urbdata) usb_free_coherent(pdata->udev, ACD_URB_BUFFER_LEN, pdata->urbdata, pdata->urb->transfer_dma);
On Wed, Nov 6, 2019 at 12:37 AM Phong Tran <tranmanphong@gmail.com> wrote: > > In context of USB disconnect, the delaywork trigger and calling > appledisplay_bl_get_brightness() and the msgdata was freed. > > add the checking return value of usb_control_msg() and only update the > data while the retval is valid. > > Reported-by: syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com > Reported-and-tested-by: > syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com > > https://groups.google.com/d/msg/syzkaller-bugs/dRmkh2UYusY/l2a6Mg3FAQAJ Hi Phong, FYI, when testing patches with the usb-fuzzer instance, you need to provide the same kernel commit id as the one where the bug was triggered. Please see here for details: > > Signed-off-by: Phong Tran <tranmanphong@gmail.com> > --- > drivers/usb/misc/appledisplay.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c > index ac92725458b5..3e3dfa5a3954 100644 > --- a/drivers/usb/misc/appledisplay.c > +++ b/drivers/usb/misc/appledisplay.c > @@ -164,7 +164,8 @@ static int appledisplay_bl_get_brightness(struct backlight_device *bd) > 0, > pdata->msgdata, 2, > ACD_USB_TIMEOUT); > - brightness = pdata->msgdata[1]; > + if (retval >= 0) > + brightness = pdata->msgdata[1]; > mutex_unlock(&pdata->sysfslock); > > if (retval < 0) > -- > 2.20.1 >
On Wed, Nov 6, 2019 at 1:10 PM Andrey Konovalov <andreyknvl@google.com> wrote: > > On Wed, Nov 6, 2019 at 12:37 AM Phong Tran <tranmanphong@gmail.com> wrote: > > > > In context of USB disconnect, the delaywork trigger and calling > > appledisplay_bl_get_brightness() and the msgdata was freed. > > > > add the checking return value of usb_control_msg() and only update the > > data while the retval is valid. > > > > Reported-by: syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com > > Reported-and-tested-by: > > syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com > > > > https://groups.google.com/d/msg/syzkaller-bugs/dRmkh2UYusY/l2a6Mg3FAQAJ > > Hi Phong, > > FYI, when testing patches with the usb-fuzzer instance, you need to > provide the same kernel commit id as the one where the bug was > triggered. Please see here for details: https://github.com/google/syzkaller/blob/master/docs/syzbot.md#usb-bugs > > > > > Signed-off-by: Phong Tran <tranmanphong@gmail.com> > > --- > > drivers/usb/misc/appledisplay.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c > > index ac92725458b5..3e3dfa5a3954 100644 > > --- a/drivers/usb/misc/appledisplay.c > > +++ b/drivers/usb/misc/appledisplay.c > > @@ -164,7 +164,8 @@ static int appledisplay_bl_get_brightness(struct backlight_device *bd) > > 0, > > pdata->msgdata, 2, > > ACD_USB_TIMEOUT); > > - brightness = pdata->msgdata[1]; > > + if (retval >= 0) > > + brightness = pdata->msgdata[1]; > > mutex_unlock(&pdata->sysfslock); > > > > if (retval < 0) > > -- > > 2.20.1 > >
Hello, syzbot has tested the proposed patch and the reproducer did not trigger crash: Reported-and-tested-by: syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com Tested on: commit: e0bd8d79 usb-fuzzer: main usb gadget fuzzer driver git tree: https://github.com/google/kasan.git kernel config: https://syzkaller.appspot.com/x/.config?x=8847e5384a16f66a dashboard link: https://syzkaller.appspot.com/bug?extid=495dab1f175edc9c2f13 compiler: gcc (GCC) 9.0.0 20181231 (experimental) patch: https://syzkaller.appspot.com/x/patch.diff?x=14d463b2e00000 Note: testing is done by a robot and is best-effort only.
On 11/6/19 6:42 PM, Oliver Neukum wrote: > Am Mittwoch, den 06.11.2019, 06:36 +0700 schrieb Phong Tran: >> In context of USB disconnect, the delaywork trigger and calling >> appledisplay_bl_get_brightness() and the msgdata was freed. >> >> add the checking return value of usb_control_msg() and only update the >> data while the retval is valid. > > Hi, > > I am afraid there are some issues with your patch. First, let me stress > that you found the right place to fix an issue and you partially fixed > an issue. But the the fix you applied is incomplete and left another > issue open. > > Your patch still allows doing IO to a device that may already be bound > to another driver. That is bad, especially as the buffer is already > free. Yes, if IO is failing, you have fixed that narrow issue. > But it need not fail. > > If you look into appledisplay_probe() you will see that it can fail > because backlight_device_register() fails. The error handling will > thereupon kill the URB and free memory. But it will not kill an already > scheduled work. The scheduled work will then call usb_control_msg() > on pdata->msgdata, which has been freed. If that IO fails, all is well. > If not, the issue still exists. > Hello Oliver, argee, there need a cancel workqueue in case error of probe(). > Secondly, your error check is off by 2. You are checking only for > usb_control_msg() failing. But it can return only one byte instead > of two. If that happens, the value you return is stale, although > the buffer is correctly allocated. > > Regards > Oliver > > The correct fix for both issues would be: > > #syz test: https://github.com/google/kasan.git e0bd8d79 > > From 2497a62bdbeb9bd94f690c22d96dd1b8cf22861f Mon Sep 17 00:00:00 2001 > From: Oliver Neukum <oneukum@suse.com> > Date: Wed, 6 Nov 2019 12:36:28 +0100 > Subject: [PATCH] appledisplay: fix error handling in the scheduled work > > The work item can operate on > > 1. stale memory left over from the last transfer > the actual length of the data transfered needs to be checked > 2. memory already freed > the error handling in appledisplay_probe() needs > to cancel the work in that case > > Signed-off-by: Oliver Neukum <oneukum@suse.com> > --- > drivers/usb/misc/appledisplay.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c > index ac92725458b5..ba1eaabc7796 100644 > --- a/drivers/usb/misc/appledisplay.c > +++ b/drivers/usb/misc/appledisplay.c > @@ -164,7 +164,12 @@ static int appledisplay_bl_get_brightness(struct backlight_device *bd) > 0, > pdata->msgdata, 2, > ACD_USB_TIMEOUT); > - brightness = pdata->msgdata[1]; > + if (retval < 2) { > + if (retval >= 0) > + retval = -EMSGSIZE; > + } else { > + brightness = pdata->msgdata[1]; > + } compare with message size (2) can be considered. if (retval == 2) { brightness = pdata->msgdata[1]; } else { retval = -EMSGSIZE; } Regards, Phong. > mutex_unlock(&pdata->sysfslock); > > if (retval < 0) > @@ -299,6 +304,7 @@ static int appledisplay_probe(struct usb_interface *iface, > if (pdata) { > if (pdata->urb) { > usb_kill_urb(pdata->urb); > + cancel_delayed_work_sync(&pdata->work); > if (pdata->urbdata) > usb_free_coherent(pdata->udev, ACD_URB_BUFFER_LEN, > pdata->urbdata, pdata->urb->transfer_dma); >
Am Mittwoch, den 06.11.2019, 21:22 +0700 schrieb Phong Tran: > compare with message size (2) can be considered. > > if (retval == 2) { > brightness = pdata->msgdata[1]; > } else { > retval = -EMSGSIZE; > } If you do it that way, the error reporting will be distorted. Hence I did it a bit more complexly. Regards Oliver
diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c index ac92725458b5..3e3dfa5a3954 100644 --- a/drivers/usb/misc/appledisplay.c +++ b/drivers/usb/misc/appledisplay.c @@ -164,7 +164,8 @@ static int appledisplay_bl_get_brightness(struct backlight_device *bd) 0, pdata->msgdata, 2, ACD_USB_TIMEOUT); - brightness = pdata->msgdata[1]; + if (retval >= 0) + brightness = pdata->msgdata[1]; mutex_unlock(&pdata->sysfslock); if (retval < 0)
In context of USB disconnect, the delaywork trigger and calling appledisplay_bl_get_brightness() and the msgdata was freed. add the checking return value of usb_control_msg() and only update the data while the retval is valid. Reported-by: syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com Reported-and-tested-by: syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com https://groups.google.com/d/msg/syzkaller-bugs/dRmkh2UYusY/l2a6Mg3FAQAJ Signed-off-by: Phong Tran <tranmanphong@gmail.com> --- drivers/usb/misc/appledisplay.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)