From: Linus Torvalds <torvalds@linux-foundation.org>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
David Howells <dhowells@redhat.com>,
Eric Biederman <ebiederm@xmission.com>,
stable <stable@vger.kernel.org>,
Christian Brauner <christian.brauner@ubuntu.com>,
Serge Hallyn <serge@hallyn.com>,
dev@opencontainers.org,
Linux Containers <containers@lists.linux-foundation.org>,
Linux API <linux-api@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC 0/1] mount: universally disallow mounting over symlinks
Date: Sun, 29 Dec 2019 23:53:47 -0800 [thread overview]
Message-ID: <CAHk-=whxNw7hYT6bJn9mVrB_a=7Y-irmpaPsp1R4xbHHkicv7g@mail.gmail.com> (raw)
In-Reply-To: <20191230072959.62kcojxpthhdwmfa@yavin.dot.cyphar.com>
On Sun, Dec 29, 2019 at 11:30 PM Aleksa Sarai <cyphar@cyphar.com> wrote:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000000
Would you mind building with debug info, and then running the oops through
scripts/decode_stacktrace.sh
which makes those addresses much more legible.
> #PF: supervisor instruction fetch in kernel mode
> #PF: error_code(0x0010) - not-present page
Somebody jumped through a NULL pointer.
> RAX: 0000000000000000 RBX: ffff906d0cc3bb40 RCX: 0000000000000abc
> RDX: 0000000000000089 RSI: ffff906d74623cc0 RDI: ffff906d74475df0
> RBP: ffff906d74475df0 R08: ffffd70b7fb24c20 R09: ffff906d066a5000
> R10: 0000000000000000 R11: 8080807fffffffff R12: ffff906d74623cc0
> R13: 0000000000000089 R14: ffffb70b82963dc0 R15: 0000000000000080
> FS: 00007fbc2a8f0540(0000) GS:ffff906dcf500000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffffffffffd6 CR3: 00000003c68f8001 CR4: 00000000003606e0
> Call Trace:
> __lookup_slow+0x94/0x160
And "__lookup_slow()" has two indirect calls (they aren't obvious with
retpoline, but look for something like
call __x86_indirect_thunk_rax
which is the modern sad way of doing "call *%rax"). One is for
revalidatinging an old dentry, but the one I _suspect_ you trigger is
this one:
old = inode->i_op->lookup(inode, dentry, flags);
but I thought we only could get here if we know it's a directory.
How did we miss the "d_can_lookup()", which is what should check that
yes, we can call that ->lookup() routine.
This is why I have that suspicion that it's somehow that O_PATH fd
opened in another process without O_PATH causes confusion...
So what I think has happened is that because of the O_PATH thing,
we've ended up with an inode that has never been truly opened (because
O_PATH skips that part), but then with the /proc/<pid>/fd/xyz open, we
now have a file descriptor that _looks_ like it is valid, and we're
treating that inode as if it can be used.
But I'm handwaving.
Linus
next prev parent reply other threads:[~2019-12-30 7:54 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-30 5:20 [PATCH RFC 0/1] mount: universally disallow mounting over symlinks Aleksa Sarai
2019-12-30 5:20 ` [PATCH RFC 1/1] " Aleksa Sarai
2019-12-30 7:34 ` Linus Torvalds
2019-12-30 8:28 ` Aleksa Sarai
2020-01-08 4:39 ` Andy Lutomirski
2019-12-30 5:44 ` [PATCH RFC 0/1] " Al Viro
2019-12-30 5:49 ` Aleksa Sarai
2019-12-30 7:29 ` Aleksa Sarai
2019-12-30 7:53 ` Linus Torvalds [this message]
2019-12-30 8:32 ` Aleksa Sarai
2020-01-02 8:58 ` David Laight
2020-01-02 9:09 ` Aleksa Sarai
2020-01-01 0:43 ` Al Viro
2020-01-01 0:54 ` Al Viro
2020-01-01 3:08 ` Al Viro
2020-01-01 14:44 ` Aleksa Sarai
2020-01-01 23:40 ` Al Viro
2020-01-02 3:59 ` Aleksa Sarai
2020-01-03 1:49 ` Al Viro
2020-01-04 4:46 ` Ian Kent
2020-01-08 3:13 ` Al Viro
2020-01-08 3:54 ` Linus Torvalds
2020-01-08 21:34 ` Al Viro
2020-01-10 0:08 ` Linus Torvalds
2020-01-10 4:15 ` Al Viro
2020-01-10 5:03 ` Linus Torvalds
2020-01-10 6:20 ` Ian Kent
2020-01-12 21:33 ` Al Viro
2020-01-13 2:59 ` Ian Kent
2020-01-14 0:25 ` Ian Kent
2020-01-14 4:39 ` Al Viro
2020-01-14 5:01 ` Ian Kent
2020-01-14 5:59 ` Ian Kent
2020-01-10 21:07 ` Aleksa Sarai
2020-01-14 4:57 ` Al Viro
2020-01-14 5:12 ` Al Viro
2020-01-14 20:01 ` Aleksa Sarai
2020-01-15 14:25 ` Al Viro
2020-01-15 14:29 ` Aleksa Sarai
2020-01-15 14:34 ` Aleksa Sarai
2020-01-15 14:48 ` Al Viro
2020-01-15 13:57 ` Aleksa Sarai
2020-01-19 3:14 ` [RFC][PATCHSET][CFT] pathwalk cleanups and fixes Al Viro
2020-01-19 14:33 ` Ian Kent
2020-01-10 23:19 ` [PATCH RFC 0/1] mount: universally disallow mounting over symlinks Al Viro
2020-01-13 1:48 ` Ian Kent
2020-01-13 3:54 ` Al Viro
2020-01-13 6:00 ` Ian Kent
2020-01-13 6:03 ` Ian Kent
2020-01-13 13:30 ` Al Viro
2020-01-14 7:25 ` Ian Kent
2020-01-14 12:17 ` Ian Kent
2020-01-04 5:52 ` Andy Lutomirski
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='CAHk-=whxNw7hYT6bJn9mVrB_a=7Y-irmpaPsp1R4xbHHkicv7g@mail.gmail.com' \
--to=torvalds@linux-foundation.org \
--cc=christian.brauner@ubuntu.com \
--cc=containers@lists.linux-foundation.org \
--cc=cyphar@cyphar.com \
--cc=dev@opencontainers.org \
--cc=dhowells@redhat.com \
--cc=ebiederm@xmission.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=serge@hallyn.com \
--cc=stable@vger.kernel.org \
--cc=viro@zeniv.linux.org.uk \
/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).