Re: [PATCH v2] rbtree: fix the red root

[Douglas Gilbert]

On 2019-01-13 10:59 p.m., Esme wrote:
> âââââââ Original Message âââââââ
> On Sunday, January 13, 2019 10:52 PM, Douglas Gilbert <dgilbert@xxxxxxxxxxxx> wrote:
>
> > On 2019-01-13 10:07 p.m., Esme wrote:
> >
> > > âââââââ Original Message âââââââ
> > > On Sunday, January 13, 2019 9:33 PM, Qian Cai cai@xxxxxx wrote:
> > >
> > > > On 1/13/19 9:20 PM, David Lechner wrote:
> > > >
> > > > > On 1/11/19 8:58 PM, Michel Lespinasse wrote:
> > > > >
> > > > > > On Fri, Jan 11, 2019 at 3:47 PM David Lechner david@xxxxxxxxxxxxxx wrote:
> > > > > >
> > > > > > > On 1/11/19 2:58 PM, Qian Cai wrote:
> > > > > > >
> > > > > > > > A GPF was reported,
> > > > > > > > kasan: CONFIG_KASAN_INLINE enabled
> > > > > > > > kasan: GPF could be caused by NULL-ptr deref or user memory access
> > > > > > > > general protection fault: 0000 [#1] SMP KASAN
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ kasan_die_handler.cold.22+0x11/0x31
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ notifier_call_chain+0x17b/0x390
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ atomic_notifier_call_chain+0xa7/0x1b0
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ notify_die+0x1be/0x2e0
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ do_general_protection+0x13e/0x330
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ general_protection+0x1e/0x30
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ rb_insert_color+0x189/0x1480
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ create_object+0x785/0xca0
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ kmemleak_alloc+0x2f/0x50
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ kmem_cache_alloc+0x1b9/0x3c0
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ getname_flags+0xdb/0x5d0
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ getname+0x1e/0x20
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ do_sys_open+0x3a1/0x7d0
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ __x64_sys_open+0x7e/0xc0
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ do_syscall_64+0x1b3/0x820
> > > > > > > >  ÂÂÂÂÂÂÂÂÂ entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > > > > > > > It turned out,
> > > > > > > > gparent = rb_red_parent(parent);
> > > > > > > > tmp = gparent->rb_right; <-- GPF was triggered here.
> > > > > > > > Apparently, "gparent" is NULL which indicates "parent" is rbtree's root
> > > > > > > > which is red. Otherwise, it will be treated properly a few lines above.
> > > > > > > > /*
> > > > > > > >  ÂÂ * If there is a black parent, we are done.
> > > > > > > >  ÂÂ * Otherwise, take some corrective action as,
> > > > > > > >  ÂÂ * per 4), we don't want a red root or two
> > > > > > > >  ÂÂ * consecutive red nodes.
> > > > > > > >  ÂÂ */
> > > > > > > > if(rb_is_black(parent))
> > > > > > > >  ÂÂÂÂÂÂ break;
> > > > > > > > Hence, it violates the rule #1 (the root can't be red) and need a fix
> > > > > > > > up, and also add a regression test for it. This looks like was
> > > > > > > > introduced by 6d58452dc06 where it no longer always paint the root as
> > > > > > > > black.
> > > > > > > > Fixes: 6d58452dc06 (rbtree: adjust root color in rb_insert_color() only
> > > > > > > > when necessary)
> > > > > > > > Reported-by: Esme esploit@xxxxxxxxxxxxx
> > > > > > > > Tested-by: Joey Pabalinas joeypabalinas@xxxxxxxxx
> > > > > > > > Signed-off-by: Qian Cai cai@xxxxxx
> > > > > > >
> > > > > > > Tested-by: David Lechner david@xxxxxxxxxxxxxx
> > > > > > > FWIW, this fixed the following crash for me:
> > > > > > > Unable to handle kernel NULL pointer dereference at virtual address 00000004
> > > > > >
> > > > > > Just to clarify, do you have a way to reproduce this crash without the fix ?
> > > > >
> > > > > I am starting to suspect that my crash was caused by some new code
> > > > > in the drm-misc-next tree that might be causing a memory corruption.
> > > > > It threw me off that the stack trace didn't contain anything related
> > > > > to drm.
> > > > > See: https://patchwork.freedesktop.org/patch/276719/
> > > >
> > > > It may be useful for those who could reproduce this issue to turn on those
> > > > memory corruption debug options to narrow down a bit.
> > > > CONFIG_DEBUG_PAGEALLOC=y
> > > > CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT=y
> > > > CONFIG_KASAN=y
> > > > CONFIG_KASAN_GENERIC=y
> > > > CONFIG_SLUB_DEBUG_ON=y
> > >
> > > I have been on SLAB, I configured SLAB DEBUG with a fresh pull from github. Linux syzkaller 5.0.0-rc2 #9 SMP Sun Jan 13 21:57:40 EST 2019 x86_64
> > > ...
> > > In an effort to get a different stack into the kernel, I felt that nothing works better than fork bomb? :)
> > > Let me know if that helps.
> > > root@syzkaller:~# gcc -o test3 test3.c
> > > root@syzkaller:~# while : ; do ./test3 & done
> >
> > And is test3 the same multi-threaded program that enters the kernel via
> > /dev/sg0 and then calls SCSI_IOCTL_SEND_COMMAND which goes to the SCSI
> > mid-level and thence to the block layer?
> >
> > And please remind me, does it also fail on lk 4.20.2 ?
> >
> > Doug Gilbert
>
> Yes, the same C repro from the earlier thread.  It was a 4.20.0 kernel where it was first detected.  I can move to 4.20.2 and see if that changes anything.

Hi,
I don't think there is any need to check lk 4.20.2 (as it would
be very surprising if it didn't also have this "feature").

More interesting might be: has "test3" been run on lk 4.19 or
any earlier kernel?

Doug Gilbert