From: David Lechner <david@lechnology.com>
To: Michel Lespinasse <walken@google.com>
Cc: Qian Cai <cai@lca.pw>, Andrew Morton <akpm@linux-foundation.org>,
esploit@protonmail.ch, jejb@linux.ibm.com, dgilbert@interlog.com,
martin.petersen@oracle.com, joeypabalinas@gmail.com,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] rbtree: fix the red root
Date: Sun, 13 Jan 2019 20:20:12 -0600 [thread overview]
Message-ID: <864d6b85-3336-4040-7c95-7d9615873777@lechnology.com> (raw)
In-Reply-To: <CANN689G0zbk7sMbQ+p9NQGQ=NWq-Q0mQOOjeFkLp19YrTfgcLg@mail.gmail.com>
On 1/11/19 8:58 PM, Michel Lespinasse wrote:
> On Fri, Jan 11, 2019 at 3:47 PM David Lechner <david@lechnology.com> 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
>>> kasan_die_handler.cold.22+0x11/0x31
>>> notifier_call_chain+0x17b/0x390
>>> atomic_notifier_call_chain+0xa7/0x1b0
>>> notify_die+0x1be/0x2e0
>>> do_general_protection+0x13e/0x330
>>> general_protection+0x1e/0x30
>>> rb_insert_color+0x189/0x1480
>>> create_object+0x785/0xca0
>>> kmemleak_alloc+0x2f/0x50
>>> kmem_cache_alloc+0x1b9/0x3c0
>>> getname_flags+0xdb/0x5d0
>>> getname+0x1e/0x20
>>> do_sys_open+0x3a1/0x7d0
>>> __x64_sys_open+0x7e/0xc0
>>> do_syscall_64+0x1b3/0x820
>>> 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.
>>>
>>> /*
>>> * If there is a black parent, we are done.
>>> * Otherwise, take some corrective action as,
>>> * per 4), we don't want a red root or two
>>> * consecutive red nodes.
>>> */
>>> if(rb_is_black(parent))
>>> 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@protonmail.ch>
>>> Tested-by: Joey Pabalinas <joeypabalinas@gmail.com>
>>> Signed-off-by: Qian Cai <cai@lca.pw>
>>> ---
>>
>> Tested-by: David Lechner <david@lechnology.com>
>> 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/
>
> I don't think the fix is correct, because it just silently ignores a
> corrupted rbtree (red root node). But the code that creates this
> situation certainly needs to be fixed - having a reproduceable test
> case would certainly help here.
>
> Regarding 6d58452dc06, the reasoning was that this code expects to be
> called after inserting a new (red) leaf into an rbtree that had all of
> its data structure invariants satisfied. So in this context, it should
> not be necessary to always reset the root to black, as this should
> already be the case...
>
next prev parent reply other threads:[~2019-01-14 2:29 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <YrcPMrGmYbPe_xgNEV6Q0jqc5XuPYmL2AFSyeNmg1gW531bgZnBGfEUK5_ktqDBaNW37b-NP2VXvlliM7_PsBRhSfB649MaW1Ne7zT9lHc=@protonmail.ch>
2019-01-11 16:51 ` [PATCH] rbtree: fix the red root Qian Cai
2019-01-11 17:17 ` Joey Pabalinas
2019-01-11 17:31 ` Matthew Wilcox
2019-01-11 17:53 ` Joey Pabalinas
2019-01-11 18:12 ` Qian Cai
2019-01-11 18:16 ` Matthew Wilcox
2019-01-11 20:58 ` [PATCH v2] " Qian Cai
2019-01-11 23:16 ` Matthew Wilcox
2019-01-12 0:18 ` Qian Cai
2019-01-12 0:39 ` Esme
2019-01-11 23:47 ` David Lechner
2019-01-12 2:58 ` Michel Lespinasse
2019-01-14 2:20 ` David Lechner [this message]
2019-01-14 2:33 ` Qian Cai
2019-01-14 3:07 ` Esme
2019-01-14 3:52 ` Douglas Gilbert
2019-01-14 3:59 ` Esme
2019-01-14 4:52 ` Douglas Gilbert
2019-01-14 6:23 ` Esme
2019-01-14 15:45 ` Qian Cai
2019-01-14 15:51 ` Esme
2019-01-14 17:58 ` Qian Cai
2019-01-14 18:26 ` Douglas Gilbert
2019-01-15 5:31 ` Qian Cai
2019-01-16 14:37 ` Esme
2019-01-18 17:10 ` Qian Cai
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=864d6b85-3336-4040-7c95-7d9615873777@lechnology.com \
--to=david@lechnology.com \
--cc=akpm@linux-foundation.org \
--cc=cai@lca.pw \
--cc=dgilbert@interlog.com \
--cc=esploit@protonmail.ch \
--cc=jejb@linux.ibm.com \
--cc=joeypabalinas@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=martin.petersen@oracle.com \
--cc=walken@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).