[v2] usb: dwc2: host: Fix use after free w/ simultaneous irqs
diff mbox

Message ID 1444863089-24636-1-git-send-email-dianders@chromium.org
State New
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Commit Message

Doug Anderson Oct. 14, 2015, 10:51 p.m. UTC
While plugging / unplugging on a DWC2 host port with "slub_debug=FZPUA"
enabled, I found a crash that was quite obviously a use after free.

It appears that in some cases when we handle the various sub-cases of
HCINT we may end up freeing the QTD.  If there is more than one bit set
in HCINT we may then end up continuing to use the QTD, which is bad.
Let's be paranoid and check for this after each sub-case.  We only do
this if there are still further bits to process, so the overhead should
be small.  This should be safe since we officially have the
"hsotg->lock" (it was grabbed in dwc2_handle_hcd_intr).

The specific crash I found was:
 Unable to handle kernel paging request at virtual address 6b6b6b9f

At the time of the crash, the kernel reported:
 (dwc2_hc_nak_intr+0x5c/0x198)
 (dwc2_handle_hcd_intr+0xa84/0xbf8)
 (_dwc2_hcd_irq+0x1c/0x20)
 (usb_hcd_irq+0x34/0x48)

Popping into kgdb found that "*qtd" was filled with "0x6b", AKA qtd had
been freed and filled with slub_debug poison.

kgdb gave a little better stack crawl:
 0 dwc2_hc_nak_intr (hsotg=hsotg@entry=0xec42e058,
     chan=chan@entry=0xec546dc0, chnum=chnum@entry=4,
     qtd=qtd@entry=0xec679600) at drivers/usb/dwc2/hcd_intr.c:1237
 1 dwc2_hc_n_intr (chnum=4, hsotg=0xec42e058) at
     drivers/usb/dwc2/hcd_intr.c:2041
 2 dwc2_hc_intr (hsotg=0xec42e058) at drivers/usb/dwc2/hcd_intr.c:2078
 3 dwc2_handle_hcd_intr (hsotg=0xec42e058) at
     drivers/usb/dwc2/hcd_intr.c:2128
 4 _dwc2_hcd_irq (hcd=<optimized out>) at drivers/usb/dwc2/hcd.c:2837
 5 usb_hcd_irq (irq=<optimized out>, __hcd=<optimized out>) at
     drivers/usb/core/hcd.c:2353

Popping up to frame #1 (dwc2_hc_n_intr) found:
 (gdb) print /x hcint
 $12 = 0x12

AKA:
 #define HCINTMSK_CHHLTD  (1 << 1)
 #define HCINTMSK_NAK     (1 << 4)

Further debugging found that by simulating receiving those two
interrupts at the same time it was trivial to replicate the
use-after-free.  See <http://crosreview.com/305712> for a patch and
instructions.  This lead to getting the following stack crawl of the
actual free:
 0  arch_kgdb_breakpoint () at arch/arm/include/asm/outercache.h:103
 1  kgdb_breakpoint () at kernel/debug/debug_core.c:1054
 2  dwc2_hcd_qtd_unlink_and_free (hsotg=<optimized out>, qh=<optimized
      out>, qtd=0xe4479a00) at drivers/usb/dwc2/hcd.h:488
 3  dwc2_deactivate_qh (free_qtd=<optimized out>, qh=0xe5efa280,
      hsotg=0xed424618) at drivers/usb/dwc2/hcd_intr.c:671
 4  dwc2_release_channel (hsotg=hsotg@entry=0xed424618,
      chan=chan@entry=0xed5be000, qtd=<optimized out>,
      halt_status=<optimized out>) at drivers/usb/dwc2/hcd_intr.c:742
 5  dwc2_halt_channel (hsotg=0xed424618, chan=0xed5be000, qtd=<optimized
      out>, halt_status=<optimized out>) at
      drivers/usb/dwc2/hcd_intr.c:804
 6  dwc2_complete_non_periodic_xfer (chnum=<optimized out>,
      halt_status=<optimized out>, qtd=<optimized out>, chan=<optimized
      out>, hsotg=<optimized out>) at drivers/usb/dwc2/hcd_intr.c:889
 7  dwc2_hc_xfercomp_intr (hsotg=hsotg@entry=0xed424618,
      chan=chan@entry=0xed5be000, chnum=chnum@entry=6,
      qtd=qtd@entry=0xe4479a00) at drivers/usb/dwc2/hcd_intr.c:1065
 8  dwc2_hc_chhltd_intr_dma (qtd=0xe4479a00, chnum=6, chan=0xed5be000,
      hsotg=0xed424618) at drivers/usb/dwc2/hcd_intr.c:1823
 9  dwc2_hc_chhltd_intr (qtd=0xe4479a00, chnum=6, chan=0xed5be000,
      hsotg=0xed424618) at drivers/usb/dwc2/hcd_intr.c:1944
 10 dwc2_hc_n_intr (chnum=6, hsotg=0xed424618) at
      drivers/usb/dwc2/hcd_intr.c:2052
 11 dwc2_hc_intr (hsotg=0xed424618) at drivers/usb/dwc2/hcd_intr.c:2097
 12 dwc2_handle_hcd_intr (hsotg=0xed424618) at
      drivers/usb/dwc2/hcd_intr.c:2147
 13 _dwc2_hcd_irq (hcd=<optimized out>) at drivers/usb/dwc2/hcd.c:2837
 14 usb_hcd_irq (irq=<optimized out>, __hcd=<optimized out>) at
      drivers/usb/core/hcd.c:2353

Though we could add specific code to handle this case, adding the
general purpose code to check for all cases where qtd might be freed
seemed safer.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
Changes in v2:
- Add static as correctly pointed by kbuild test robot

 drivers/usb/dwc2/hcd_intr.c | 80 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 70 insertions(+), 10 deletions(-)

Comments

John Youn Oct. 15, 2015, 11:21 p.m. UTC | #1
On 10/14/2015 3:51 PM, Douglas Anderson wrote:
> While plugging / unplugging on a DWC2 host port with "slub_debug=FZPUA"
> enabled, I found a crash that was quite obviously a use after free.
> 
> It appears that in some cases when we handle the various sub-cases of
> HCINT we may end up freeing the QTD.  If there is more than one bit set
> in HCINT we may then end up continuing to use the QTD, which is bad.
> Let's be paranoid and check for this after each sub-case.  We only do
> this if there are still further bits to process, so the overhead should
> be small.  This should be safe since we officially have the
> "hsotg->lock" (it was grabbed in dwc2_handle_hcd_intr).
> 
> The specific crash I found was:
>  Unable to handle kernel paging request at virtual address 6b6b6b9f
> 
> At the time of the crash, the kernel reported:
>  (dwc2_hc_nak_intr+0x5c/0x198)
>  (dwc2_handle_hcd_intr+0xa84/0xbf8)
>  (_dwc2_hcd_irq+0x1c/0x20)
>  (usb_hcd_irq+0x34/0x48)
> 
> Popping into kgdb found that "*qtd" was filled with "0x6b", AKA qtd had
> been freed and filled with slub_debug poison.
> 
> kgdb gave a little better stack crawl:
>  0 dwc2_hc_nak_intr (hsotg=hsotg@entry=0xec42e058,
>      chan=chan@entry=0xec546dc0, chnum=chnum@entry=4,
>      qtd=qtd@entry=0xec679600) at drivers/usb/dwc2/hcd_intr.c:1237
>  1 dwc2_hc_n_intr (chnum=4, hsotg=0xec42e058) at
>      drivers/usb/dwc2/hcd_intr.c:2041
>  2 dwc2_hc_intr (hsotg=0xec42e058) at drivers/usb/dwc2/hcd_intr.c:2078
>  3 dwc2_handle_hcd_intr (hsotg=0xec42e058) at
>      drivers/usb/dwc2/hcd_intr.c:2128
>  4 _dwc2_hcd_irq (hcd=<optimized out>) at drivers/usb/dwc2/hcd.c:2837
>  5 usb_hcd_irq (irq=<optimized out>, __hcd=<optimized out>) at
>      drivers/usb/core/hcd.c:2353
> 
> Popping up to frame #1 (dwc2_hc_n_intr) found:
>  (gdb) print /x hcint
>  $12 = 0x12
> 
> AKA:
>  #define HCINTMSK_CHHLTD  (1 << 1)
>  #define HCINTMSK_NAK     (1 << 4)
> 
> Further debugging found that by simulating receiving those two
> interrupts at the same time it was trivial to replicate the
> use-after-free.  See <http://crosreview.com/305712> for a patch and
> instructions.  This lead to getting the following stack crawl of the
> actual free:
>  0  arch_kgdb_breakpoint () at arch/arm/include/asm/outercache.h:103
>  1  kgdb_breakpoint () at kernel/debug/debug_core.c:1054
>  2  dwc2_hcd_qtd_unlink_and_free (hsotg=<optimized out>, qh=<optimized
>       out>, qtd=0xe4479a00) at drivers/usb/dwc2/hcd.h:488
>  3  dwc2_deactivate_qh (free_qtd=<optimized out>, qh=0xe5efa280,
>       hsotg=0xed424618) at drivers/usb/dwc2/hcd_intr.c:671
>  4  dwc2_release_channel (hsotg=hsotg@entry=0xed424618,
>       chan=chan@entry=0xed5be000, qtd=<optimized out>,
>       halt_status=<optimized out>) at drivers/usb/dwc2/hcd_intr.c:742
>  5  dwc2_halt_channel (hsotg=0xed424618, chan=0xed5be000, qtd=<optimized
>       out>, halt_status=<optimized out>) at
>       drivers/usb/dwc2/hcd_intr.c:804
>  6  dwc2_complete_non_periodic_xfer (chnum=<optimized out>,
>       halt_status=<optimized out>, qtd=<optimized out>, chan=<optimized
>       out>, hsotg=<optimized out>) at drivers/usb/dwc2/hcd_intr.c:889
>  7  dwc2_hc_xfercomp_intr (hsotg=hsotg@entry=0xed424618,
>       chan=chan@entry=0xed5be000, chnum=chnum@entry=6,
>       qtd=qtd@entry=0xe4479a00) at drivers/usb/dwc2/hcd_intr.c:1065
>  8  dwc2_hc_chhltd_intr_dma (qtd=0xe4479a00, chnum=6, chan=0xed5be000,
>       hsotg=0xed424618) at drivers/usb/dwc2/hcd_intr.c:1823
>  9  dwc2_hc_chhltd_intr (qtd=0xe4479a00, chnum=6, chan=0xed5be000,
>       hsotg=0xed424618) at drivers/usb/dwc2/hcd_intr.c:1944
>  10 dwc2_hc_n_intr (chnum=6, hsotg=0xed424618) at
>       drivers/usb/dwc2/hcd_intr.c:2052
>  11 dwc2_hc_intr (hsotg=0xed424618) at drivers/usb/dwc2/hcd_intr.c:2097
>  12 dwc2_handle_hcd_intr (hsotg=0xed424618) at
>       drivers/usb/dwc2/hcd_intr.c:2147
>  13 _dwc2_hcd_irq (hcd=<optimized out>) at drivers/usb/dwc2/hcd.c:2837
>  14 usb_hcd_irq (irq=<optimized out>, __hcd=<optimized out>) at
>       drivers/usb/core/hcd.c:2353
> 
> Though we could add specific code to handle this case, adding the
> general purpose code to check for all cases where qtd might be freed
> seemed safer.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> Changes in v2:
> - Add static as correctly pointed by kbuild test robot
> 
>  drivers/usb/dwc2/hcd_intr.c | 80 +++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 70 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/usb/dwc2/hcd_intr.c b/drivers/usb/dwc2/hcd_intr.c
> index f70c970..1156e13 100644
> --- a/drivers/usb/dwc2/hcd_intr.c
> +++ b/drivers/usb/dwc2/hcd_intr.c
> @@ -1949,6 +1949,25 @@ static void dwc2_hc_chhltd_intr(struct dwc2_hsotg *hsotg,
>  	}
>  }
>  
> +/*
> + * Check if the given qtd is still the top of the list (and thus valid).
> + *
> + * If dwc2_hcd_qtd_unlink_and_free() has been called since we grabbed
> + * the qtd from the top of the list, this will return NULL.  Otherwise
> + * it will be passed back qtd.
> + */
> +static struct dwc2_qtd *dwc2_check_qtd_still_ok(struct dwc2_qtd *qtd,
> +						struct list_head *qtd_list)
> +{
> +	struct dwc2_qtd *cur_head;
> +
> +	cur_head = list_first_entry(qtd_list, struct dwc2_qtd, qtd_list_entry);
> +	if (cur_head == qtd)
> +		return qtd;
> +
> +	return NULL;
> +}
> +
>  /* Handles interrupt for a specific Host Channel */
>  static void dwc2_hc_n_intr(struct dwc2_hsotg *hsotg, int chnum)
>  {
> @@ -2031,26 +2050,67 @@ static void dwc2_hc_n_intr(struct dwc2_hsotg *hsotg, int chnum)
>  		 */
>  		hcint &= ~HCINTMSK_NYET;
>  	}
> -	if (hcint & HCINTMSK_CHHLTD)
> +
> +	if (hcint & HCINTMSK_CHHLTD) {
> +		hcint &= ~HCINTMSK_CHHLTD;
>  		dwc2_hc_chhltd_intr(hsotg, chan, chnum, qtd);
> -	if (hcint & HCINTMSK_AHBERR)
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
> +	if (hcint & HCINTMSK_AHBERR) {
> +		hcint &= ~HCINTMSK_AHBERR;
>  		dwc2_hc_ahberr_intr(hsotg, chan, chnum, qtd);
> -	if (hcint & HCINTMSK_STALL)
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
> +	if (hcint & HCINTMSK_STALL) {
> +		hcint &= ~HCINTMSK_STALL;
>  		dwc2_hc_stall_intr(hsotg, chan, chnum, qtd);
> -	if (hcint & HCINTMSK_NAK)
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
> +	if (hcint & HCINTMSK_NAK) {
> +		hcint &= ~HCINTMSK_NAK;
>  		dwc2_hc_nak_intr(hsotg, chan, chnum, qtd);
> -	if (hcint & HCINTMSK_ACK)
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
> +	if (hcint & HCINTMSK_ACK) {
> +		hcint &= ~HCINTMSK_ACK;
>  		dwc2_hc_ack_intr(hsotg, chan, chnum, qtd);
> -	if (hcint & HCINTMSK_NYET)
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
> +	if (hcint & HCINTMSK_NYET) {
> +		hcint &= ~HCINTMSK_NYET;
>  		dwc2_hc_nyet_intr(hsotg, chan, chnum, qtd);
> -	if (hcint & HCINTMSK_XACTERR)
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
> +	if (hcint & HCINTMSK_XACTERR) {
> +		hcint &= ~HCINTMSK_XACTERR;
>  		dwc2_hc_xacterr_intr(hsotg, chan, chnum, qtd);
> -	if (hcint & HCINTMSK_BBLERR)
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
> +	if (hcint & HCINTMSK_BBLERR) {
> +		hcint &= ~HCINTMSK_BBLERR;
>  		dwc2_hc_babble_intr(hsotg, chan, chnum, qtd);
> -	if (hcint & HCINTMSK_FRMOVRUN)
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
> +	if (hcint & HCINTMSK_FRMOVRUN) {
> +		hcint &= ~HCINTMSK_FRMOVRUN;
>  		dwc2_hc_frmovrun_intr(hsotg, chan, chnum, qtd);
> -	if (hcint & HCINTMSK_DATATGLERR)
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
> +	if (hcint & HCINTMSK_DATATGLERR) {
> +		hcint &= ~HCINTMSK_DATATGLERR;
>  		dwc2_hc_datatglerr_intr(hsotg, chan, chnum, qtd);
> +		if (hcint)
> +			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
> +	}
>  
>  	chan->hcint = 0;
>  }
> 

Passing a NULL qtd to some of the subcases will lead to a NULL
pointer dereference in that function or some function that it
calls.

I think you could just check the qtd after each call and bail if
it's not ok.

John
Doug Anderson Oct. 15, 2015, 11:38 p.m. UTC | #2
John,

On Thu, Oct 15, 2015 at 4:21 PM, John Youn <John.Youn@synopsys.com> wrote:
> Passing a NULL qtd to some of the subcases will lead to a NULL
> pointer dereference in that function or some function that it
> calls.
>
> I think you could just check the qtd after each call and bail if
> it's not ok.

I worry a little bit about ignoring an interrupt that we've already
acknowledged, but if you think that's safer I can certainly change the
patch.

-Doug
John Youn Oct. 16, 2015, 7:57 a.m. UTC | #3
On 10/15/2015 4:38 PM, Doug Anderson wrote:
> John,
> 
> On Thu, Oct 15, 2015 at 4:21 PM, John Youn <John.Youn@synopsys.com> wrote:
>> Passing a NULL qtd to some of the subcases will lead to a NULL
>> pointer dereference in that function or some function that it
>> calls.
>>
>> I think you could just check the qtd after each call and bail if
>> it's not ok.
> 
> I worry a little bit about ignoring an interrupt that we've already
> acknowledged, but if you think that's safer I can certainly change the
> patch.
> 

In terms of avoiding crashes it's probably safer.

Whether it is correct or not, I'm not sure. I need to review the
code more.

The question is: after the qtd has been freed, is anything the
other handlers do necessary? Might have to look at each case
separately.

John

Patch
diff mbox

diff --git a/drivers/usb/dwc2/hcd_intr.c b/drivers/usb/dwc2/hcd_intr.c
index f70c970..1156e13 100644
--- a/drivers/usb/dwc2/hcd_intr.c
+++ b/drivers/usb/dwc2/hcd_intr.c
@@ -1949,6 +1949,25 @@  static void dwc2_hc_chhltd_intr(struct dwc2_hsotg *hsotg,
 	}
 }
 
+/*
+ * Check if the given qtd is still the top of the list (and thus valid).
+ *
+ * If dwc2_hcd_qtd_unlink_and_free() has been called since we grabbed
+ * the qtd from the top of the list, this will return NULL.  Otherwise
+ * it will be passed back qtd.
+ */
+static struct dwc2_qtd *dwc2_check_qtd_still_ok(struct dwc2_qtd *qtd,
+						struct list_head *qtd_list)
+{
+	struct dwc2_qtd *cur_head;
+
+	cur_head = list_first_entry(qtd_list, struct dwc2_qtd, qtd_list_entry);
+	if (cur_head == qtd)
+		return qtd;
+
+	return NULL;
+}
+
 /* Handles interrupt for a specific Host Channel */
 static void dwc2_hc_n_intr(struct dwc2_hsotg *hsotg, int chnum)
 {
@@ -2031,26 +2050,67 @@  static void dwc2_hc_n_intr(struct dwc2_hsotg *hsotg, int chnum)
 		 */
 		hcint &= ~HCINTMSK_NYET;
 	}
-	if (hcint & HCINTMSK_CHHLTD)
+
+	if (hcint & HCINTMSK_CHHLTD) {
+		hcint &= ~HCINTMSK_CHHLTD;
 		dwc2_hc_chhltd_intr(hsotg, chan, chnum, qtd);
-	if (hcint & HCINTMSK_AHBERR)
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
+	if (hcint & HCINTMSK_AHBERR) {
+		hcint &= ~HCINTMSK_AHBERR;
 		dwc2_hc_ahberr_intr(hsotg, chan, chnum, qtd);
-	if (hcint & HCINTMSK_STALL)
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
+	if (hcint & HCINTMSK_STALL) {
+		hcint &= ~HCINTMSK_STALL;
 		dwc2_hc_stall_intr(hsotg, chan, chnum, qtd);
-	if (hcint & HCINTMSK_NAK)
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
+	if (hcint & HCINTMSK_NAK) {
+		hcint &= ~HCINTMSK_NAK;
 		dwc2_hc_nak_intr(hsotg, chan, chnum, qtd);
-	if (hcint & HCINTMSK_ACK)
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
+	if (hcint & HCINTMSK_ACK) {
+		hcint &= ~HCINTMSK_ACK;
 		dwc2_hc_ack_intr(hsotg, chan, chnum, qtd);
-	if (hcint & HCINTMSK_NYET)
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
+	if (hcint & HCINTMSK_NYET) {
+		hcint &= ~HCINTMSK_NYET;
 		dwc2_hc_nyet_intr(hsotg, chan, chnum, qtd);
-	if (hcint & HCINTMSK_XACTERR)
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
+	if (hcint & HCINTMSK_XACTERR) {
+		hcint &= ~HCINTMSK_XACTERR;
 		dwc2_hc_xacterr_intr(hsotg, chan, chnum, qtd);
-	if (hcint & HCINTMSK_BBLERR)
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
+	if (hcint & HCINTMSK_BBLERR) {
+		hcint &= ~HCINTMSK_BBLERR;
 		dwc2_hc_babble_intr(hsotg, chan, chnum, qtd);
-	if (hcint & HCINTMSK_FRMOVRUN)
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
+	if (hcint & HCINTMSK_FRMOVRUN) {
+		hcint &= ~HCINTMSK_FRMOVRUN;
 		dwc2_hc_frmovrun_intr(hsotg, chan, chnum, qtd);
-	if (hcint & HCINTMSK_DATATGLERR)
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
+	if (hcint & HCINTMSK_DATATGLERR) {
+		hcint &= ~HCINTMSK_DATATGLERR;
 		dwc2_hc_datatglerr_intr(hsotg, chan, chnum, qtd);
+		if (hcint)
+			qtd = dwc2_check_qtd_still_ok(qtd, &chan->qh->qtd_list);
+	}
 
 	chan->hcint = 0;
 }