From: Aleksa Sarai <cyphar@cyphar.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
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: Mon, 30 Dec 2019 19:32:24 +1100 [thread overview]
Message-ID: <20191230083224.sbk2jspqmup43obs@yavin.dot.cyphar.com> (raw)
In-Reply-To: <CAHk-=whxNw7hYT6bJn9mVrB_a=7Y-irmpaPsp1R4xbHHkicv7g@mail.gmail.com>
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On 2019-12-29, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> 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.
Will do.
> > #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.
I'll try applying a trivial patch to add d_can_lookup() to see if it
fixes the immediate issue.
> 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.
I'm not sure I agree -- as I mentioned in my other mail, re-opening
through /proc/self/fd/$n works *very* well and has for a long time (in
fact, both LXC and runc depend on this working).
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>
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next prev parent reply other threads:[~2019-12-30 8:32 UTC|newest]
Thread overview: 91+ 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
[not found] ` <20191230072959.62kcojxpthhdwmfa@yavin.dot.cyphar.com>
2019-12-30 7:53 ` Linus Torvalds
2019-12-30 8:32 ` Aleksa Sarai [this message]
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
2020-01-18 12:07 ` [PATCH v3 0/2] openat2: minor uapi cleanups Aleksa Sarai
2020-01-18 12:07 ` [PATCH v3 1/2] open: introduce openat2(2) syscall Aleksa Sarai
2020-01-18 12:08 ` [PATCH v3 2/2] selftests: add openat2(2) selftests Aleksa Sarai
2020-01-18 15:28 ` [PATCH v3 0/2] openat2: minor uapi cleanups Al Viro
2020-01-18 18:09 ` Al Viro
2020-01-18 23:03 ` Aleksa Sarai
2020-01-19 1:12 ` Al Viro
2020-01-15 13:57 ` [PATCH RFC 0/1] mount: universally disallow mounting over symlinks Aleksa Sarai
2020-01-19 3:14 ` [RFC][PATCHSET][CFT] pathwalk cleanups and fixes Al Viro
2020-01-19 3:17 ` [PATCH 01/17] do_add_mount(): lift lock_mount/unlock_mount into callers Al Viro
2020-01-19 3:17 ` [PATCH 02/17] fix automount/automount race properly Al Viro
2020-01-30 14:34 ` Christian Brauner
2020-01-19 3:17 ` [PATCH 03/17] follow_automount(): get rid of dead^Wstillborn code Al Viro
2020-01-30 14:38 ` Christian Brauner
2020-01-19 3:17 ` [PATCH 04/17] follow_automount() doesn't need the entire nameidata Al Viro
2020-01-30 14:45 ` Christian Brauner
2020-01-30 15:38 ` Al Viro
2020-01-30 15:55 ` Al Viro
2020-01-19 3:17 ` [PATCH 05/17] make build_open_flags() treat O_CREAT | O_EXCL as implying O_NOFOLLOW Al Viro
2020-01-19 3:17 ` [PATCH 06/17] handle_mounts(): start building a sane wrapper for follow_managed() Al Viro
2020-01-19 3:17 ` [PATCH 07/17] atomic_open(): saner calling conventions (return dentry on success) Al Viro
2020-01-19 3:17 ` [PATCH 08/17] lookup_open(): " Al Viro
2020-01-19 3:17 ` [PATCH 09/17] do_last(): collapse the call of path_to_nameidata() Al Viro
2020-01-19 3:17 ` [PATCH 10/17] handle_mounts(): pass dentry in, turn path into a pure out argument Al Viro
2020-01-19 3:17 ` [PATCH 11/17] lookup_fast(): consolidate the RCU success case Al Viro
2020-01-19 3:17 ` [PATCH 12/17] teach handle_mounts() to handle RCU mode Al Viro
2020-01-19 3:17 ` [PATCH 13/17] lookup_fast(): take mount traversal into callers Al Viro
2020-01-19 3:17 ` [PATCH 14/17] new step_into() flag: WALK_NOFOLLOW Al Viro
2020-01-19 3:17 ` [PATCH 15/17] fold handle_mounts() into step_into() Al Viro
2020-01-19 3:17 ` [PATCH 16/17] LOOKUP_MOUNTPOINT: fold path_mountpointat() into path_lookupat() Al Viro
2020-01-19 3:17 ` [PATCH 17/17] expand the only remaining call of path_lookup_conditional() Al Viro
2020-01-19 3:17 ` [PATCH 1/9] merging pick_link() with get_link(), part 1 Al Viro
2020-01-19 3:17 ` [PATCH 2/9] merging pick_link() with get_link(), part 2 Al Viro
2020-01-19 3:17 ` [PATCH 3/9] merging pick_link() with get_link(), part 3 Al Viro
2020-01-19 3:17 ` [PATCH 4/9] merging pick_link() with get_link(), part 4 Al Viro
2020-01-19 3:17 ` [PATCH 5/9] merging pick_link() with get_link(), part 5 Al Viro
2020-01-19 3:17 ` [PATCH 6/9] merging pick_link() with get_link(), part 6 Al Viro
2020-01-19 3:17 ` [PATCH 7/9] finally fold get_link() into pick_link() Al Viro
2020-01-19 3:17 ` [PATCH 8/9] massage __follow_mount_rcu() a bit Al Viro
2020-01-19 3:17 ` [PATCH 9/9] new helper: traverse_mounts() Al Viro
2020-01-30 14:13 ` [PATCH 01/17] do_add_mount(): lift lock_mount/unlock_mount into callers Christian Brauner
2020-01-19 14:33 ` [RFC][PATCHSET][CFT] pathwalk cleanups and fixes 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
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