From: Dmitry Vyukov <dvyukov@google.com>
To: Dominique Martinet <asmadeus@codewreck.org>
Cc: syzbot <syzbot+0c1d61e4db7db94102ca@syzkaller.appspotmail.com>,
David Miller <davem@davemloft.net>,
Eric Van Hensbergen <ericvh@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Latchesar Ionkov <lucho@ionkov.net>,
netdev <netdev@vger.kernel.org>,
syzkaller-bugs@googlegroups.com,
v9fs-developer@lists.sourceforge.net
Subject: Re: WARNING in kmem_cache_create_usercopy
Date: Tue, 6 Nov 2018 18:29:36 -0800 [thread overview]
Message-ID: <CACT4Y+bu52epUKjx5PEQBmhuvjA-wk8xbO4XpeAYHHZZkxAn3w@mail.gmail.com> (raw)
In-Reply-To: <20181102223908.GA9565@nautica>
On Fri, Nov 2, 2018 at 3:39 PM, Dominique Martinet
<asmadeus@codewreck.org> wrote:
> syzbot wrote on Fri, Nov 02, 2018:
>> RIP: 0010:kmem_cache_create_usercopy+0xad/0x240 mm/slab_common.c:473
>> Code: 44 89 f0 25 00 60 de 04 45 85 ed 89 45 cc 75 0b 8b 45 d0 85 c0
>> 0f 85 8e 01 00 00 44 39 eb 72 0a 89 d8 44 29 e8 3b 45 d0 73 7e <0f>
>> 0b c7 45 d0 00 00 00 00 4c 8b 45 10 44 89 fa 89 de 4c 89 e7 8b
>> RSP: 0018:ffff8801bc23f5d0 EFLAGS: 00010213
>> RAX: 0000000000000000 RBX: 0000000000000008 RCX: 0000000000000006
>> RDX: 0000000000000000 RSI: 0000000000000020 RDI: ffffffff88b04b20
>> RBP: ffff8801bc23f608 R08: fffffbfff1283a2d R09: fffffbfff1283a2c
>> R10: ffff8801bc23f5c0 R11: ffffffff8941d167 R12: ffffffff88b04b20
>> R13: 00000000fffffffd R14: 0000000000000000 R15: 0000000000000000
>> p9_client_create+0xa58/0x1769 net/9p/client.c:1054
>
> No lower bound on msize, the reproducer gives a reply from the
> pseudo-server with msize=8 and we happily take it, underflowing the
> msize - 11 (hdr+4) argument to kmem_cache_create_usercopy...
> This probably never worked anyway, but we now get a warning :)
>
>
> We need to add a sane lower bound to msize as well as the current upper
> bound set in the transport.
> We have some header sizes in 9p.h for IO header overhead (P9_IOHDRSZ to
> 24 for example) but I think that's too low in practice; stuff like
> readdir will require more than this to get a single entry... We can
> request the server to ask for at least 4k?
> 9p would probably work with less (e.g. 1k; I'd rather not have to
> figgure the minimum length we need to get each messages to work in its
> minimal form) but honestly even with 4k the perforamnces will be
> terrible, so tempted to go with that...
>
> I'll send a patch imposing 4k next week unless someone else does first,
> or replies indicate different preferences.
>
>
> @Dmitry: semi-related, the C reproducer (
> https://syzkaller.appspot.com/x/repro.c?x=1701f831400000 ) has a lot of
> "readable" letters spelled out as "\x63..." or chars as 0x3d - it's fine
> for generated code and that might be easier for the intermediate
> representation syzkaller works with, but do you know something handy
> that would help convert these to readable strings?
> e.g. "\x63\x61\x63\x68\x65\x3d\xc0\x6d\x61\x70" could be written
> "cache=\xc0map", and 0x3d as '=' (hm I guess the later would not always
> make sense to convert so probably best left as is, but it gets annoying
> pretty fast with longer strings)
Hi Dominique,
I've filed https://github.com/google/syzkaller/issues/792 for this.
Thanks for the feedback.
prev parent reply other threads:[~2018-11-07 2:30 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-02 15:37 WARNING in kmem_cache_create_usercopy syzbot
2018-11-02 22:39 ` Dominique Martinet
2018-11-05 8:52 ` [PATCH] 9p/net: put a lower bound on msize Dominique Martinet
2018-11-20 6:03 ` Dominique Martinet
2018-11-07 2:29 ` Dmitry Vyukov [this message]
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=CACT4Y+bu52epUKjx5PEQBmhuvjA-wk8xbO4XpeAYHHZZkxAn3w@mail.gmail.com \
--to=dvyukov@google.com \
--cc=asmadeus@codewreck.org \
--cc=davem@davemloft.net \
--cc=ericvh@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=lucho@ionkov.net \
--cc=netdev@vger.kernel.org \
--cc=syzbot+0c1d61e4db7db94102ca@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=v9fs-developer@lists.sourceforge.net \
/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).