[PATCH v4] usb: dwc2: host: Fix use after free w/ simultaneous irqs
John Youn
John.Youn at synopsys.com
Fri Oct 16 21:14:29 PDT 2015
On 10/16/2015 4:02 PM, Douglas Anderson wrote:
> From: Doug Anderson <dianders at chromium.org>
>
> 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. 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 at entry=0xec42e058,
> chan=chan at entry=0xec546dc0, chnum=chnum at entry=4,
> qtd=qtd at 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 at entry=0xed424618,
> chan=chan at 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 at entry=0xed424618,
> chan=chan at entry=0xed5be000, chnum=chnum at entry=6,
> qtd=qtd at 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 at chromium.org>
> ---
> Changes in v4:
> - Fix NULL qh case
>
> Changes in v3:
> - Don't pass NULL if qtd freed, just return (John Youn)
> - Don't keep track of interrupts left: list_first_entry() is fast.
>
> Changes in v2:
> - Add static as correctly pointed by kbuild test robot
>
> drivers/usb/dwc2/hcd_intr.c | 70 ++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 60 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/usb/dwc2/hcd_intr.c b/drivers/usb/dwc2/hcd_intr.c
> index f70c970..bda0b21 100644
> --- a/drivers/usb/dwc2/hcd_intr.c
> +++ b/drivers/usb/dwc2/hcd_intr.c
> @@ -1949,6 +1949,24 @@ 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 false (otherwise true).
> + */
> +static bool dwc2_check_qtd_still_ok(struct dwc2_qtd *qtd, struct dwc2_qh *qh)
> +{
> + struct dwc2_qtd *cur_head;
> +
> + if (qh == NULL)
> + return false;
> +
> + cur_head = list_first_entry(&qh->qtd_list, struct dwc2_qtd,
> + qtd_list_entry);
> + return (cur_head == qtd);
> +}
> +
> /* Handles interrupt for a specific Host Channel */
> static void dwc2_hc_n_intr(struct dwc2_hsotg *hsotg, int chnum)
> {
> @@ -2031,27 +2049,59 @@ static void dwc2_hc_n_intr(struct dwc2_hsotg *hsotg, int chnum)
> */
> hcint &= ~HCINTMSK_NYET;
> }
> - if (hcint & HCINTMSK_CHHLTD)
> +
> + if (hcint & HCINTMSK_CHHLTD) {
> dwc2_hc_chhltd_intr(hsotg, chan, chnum, qtd);
> - if (hcint & HCINTMSK_AHBERR)
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
> + if (hcint & HCINTMSK_AHBERR) {
> dwc2_hc_ahberr_intr(hsotg, chan, chnum, qtd);
> - if (hcint & HCINTMSK_STALL)
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
> + if (hcint & HCINTMSK_STALL) {
> dwc2_hc_stall_intr(hsotg, chan, chnum, qtd);
> - if (hcint & HCINTMSK_NAK)
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
> + if (hcint & HCINTMSK_NAK) {
> dwc2_hc_nak_intr(hsotg, chan, chnum, qtd);
> - if (hcint & HCINTMSK_ACK)
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
> + if (hcint & HCINTMSK_ACK) {
> dwc2_hc_ack_intr(hsotg, chan, chnum, qtd);
> - if (hcint & HCINTMSK_NYET)
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
> + if (hcint & HCINTMSK_NYET) {
> dwc2_hc_nyet_intr(hsotg, chan, chnum, qtd);
> - if (hcint & HCINTMSK_XACTERR)
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
> + if (hcint & HCINTMSK_XACTERR) {
> dwc2_hc_xacterr_intr(hsotg, chan, chnum, qtd);
> - if (hcint & HCINTMSK_BBLERR)
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
> + if (hcint & HCINTMSK_BBLERR) {
> dwc2_hc_babble_intr(hsotg, chan, chnum, qtd);
> - if (hcint & HCINTMSK_FRMOVRUN)
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
> + if (hcint & HCINTMSK_FRMOVRUN) {
> dwc2_hc_frmovrun_intr(hsotg, chan, chnum, qtd);
> - if (hcint & HCINTMSK_DATATGLERR)
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
> + if (hcint & HCINTMSK_DATATGLERR) {
> dwc2_hc_datatglerr_intr(hsotg, chan, chnum, qtd);
> + if (!dwc2_check_qtd_still_ok(qtd, chan->qh))
> + goto exit;
> + }
>
> +exit:
> chan->hcint = 0;
> }
>
>
I reviewed this some more and I think this should be ok. Most of
the handlers don't make sense without a qtd and/or channel.
Although I am not completely sure on the desc dma case. I think
it will at least be better than letting the use-after-free occur.
Acked-by: John Youn <johnyoun at synopsys.com>
John
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