Hi, On Fri, Oct 16, 2015 at 2:59 PM, Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: > From: Doug Anderson <dianders@xxxxxxxxxxxx> > > 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@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@xxxxxxxxxxxx> > --- > 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 | 67 ++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 57 insertions(+), 10 deletions(-) I just tested this latest patch together with the descriptor DMA patches. I didn't track down why, but something about that series ended up making "qh" NULL after an interrupt. I'll post up v4 that fixes that. Sorry for the noise. -Doug -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
