From: Jiri Kosina <jikos@kernel.org>
To: Eric Biggers <ebiggers@kernel.org>
Cc: David Herrmann <dh.herrmann@googlemail.com>,
Benjamin Tissoires <benjamin.tissoires@redhat.com>,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
syzkaller-bugs@googlegroups.com,
Dmitry Vyukov <dvyukov@google.com>,
Dmitry Torokhov <dtor@google.com>,
syzbot+72473edc9bf4eb1c6556@syzkaller.appspotmail.com,
stable@vger.kernel.org, Jann Horn <jannh@google.com>,
Andy Lutomirski <luto@kernel.org>,
David Herrmann <dh.herrmann@gmail.com>
Subject: Re: [PATCH v2] HID: uhid: forbid UHID_CREATE under KERNEL_DS or elevated privileges
Date: Mon, 19 Nov 2018 13:52:28 +0100 (CET) [thread overview]
Message-ID: <nycvar.YFH.7.76.1811191351020.21108@cbobk.fhfr.pm> (raw)
In-Reply-To: <20181114215509.163600-1-ebiggers@kernel.org>
[ David added to CC ]
On Wed, 14 Nov 2018, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> When a UHID_CREATE command is written to the uhid char device, a
> copy_from_user() is done from a user pointer embedded in the command.
> When the address limit is KERNEL_DS, e.g. as is the case during
> sys_sendfile(), this can read from kernel memory. Alternatively,
> information can be leaked from a setuid binary that is tricked to write
> to the file descriptor. Therefore, forbid UHID_CREATE in these cases.
>
> No other commands in uhid_char_write() are affected by this bug and
> UHID_CREATE is marked as "obsolete", so apply the restriction to
> UHID_CREATE only rather than to uhid_char_write() entirely.
>
> Thanks to Dmitry Vyukov for adding uhid definitions to syzkaller and to
> Jann Horn for commit 9da3f2b740544 ("x86/fault: BUG() when uaccess
> helpers fault on kernel addresses"), allowing this bug to be found.
>
> Reported-by: syzbot+72473edc9bf4eb1c6556@syzkaller.appspotmail.com
> Fixes: d365c6cfd337 ("HID: uhid: add UHID_CREATE and UHID_DESTROY events")
> Cc: <stable@vger.kernel.org> # v3.6+
> Cc: Jann Horn <jannh@google.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
Thanks for the patch. I however believe the fix below is more generic, and
would prefer taking that one in case noone sees any major flaw in that
I've overlooked. Thanks.
From: David Herrmann <dh.herrmann@gmail.com>
Subject: [PATCH] HID: uhid: prevent splice(2)
The kernel has a default implementation of splice(2) for writing from a
pipe into an arbitrary file. This behavior can be overriden by
providing an f_op.splice_write() callback.
Unfortunately, the default implementation of splice_write() takes page
by page from the source pipe, calls kmap() and passes the mapped page
as kernel-address to f_op.write(). Thus, it uses standard write(2) to
implement splice(2). However, since the page is kernel-mapped, they
have to `set_fs(get_ds())`. This is mostly fine, but UHID takes
command-streams through write(2), and thus it might interpret the data
taken as pointers. If called with KERNEL_DS, you can trick UHID to
allow kernel-space pointers as well.
As a simple fix, prevent splice(2) on UHID. It is unsecure, but it is
also non-functional. We need a linear mapping of the input in UHID, so
chunked input from splice(2) makes no sense, anyway.
Reported-by: syzbot+72473edc9bf4eb1c6556@syzkaller.appspotmail.com
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
---
drivers/hid/uhid.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 3c5507313606..fefedc0b4dc6 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -753,6 +753,15 @@ static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
return ret ? ret : count;
}
+static ssize_t uhid_char_splice_write(struct pipe_inode_info *pipe,
+ struct file *out,
+ loff_t *ppos,
+ size_t len,
+ unsigned int flags)
+{
+ return -EOPNOTSUPP;
+}
+
static __poll_t uhid_char_poll(struct file *file, poll_table *wait)
{
struct uhid_device *uhid = file->private_data;
@@ -771,6 +780,7 @@ static const struct file_operations uhid_fops = {
.release = uhid_char_release,
.read = uhid_char_read,
.write = uhid_char_write,
+ .splice_write = uhid_char_splice_write,
.poll = uhid_char_poll,
.llseek = no_llseek,
};
--
Jiri Kosina
SUSE Labs
next prev parent reply other threads:[~2018-11-19 12:52 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-11 18:26 BUG: GPF in non-whitelisted uaccess (non-canonical address?) syzbot
2018-11-14 0:25 ` syzbot
2018-11-14 12:20 ` David Herrmann
2018-11-14 16:52 ` Dmitry Vyukov
2018-11-14 17:14 ` Eric Biggers
2018-11-14 18:02 ` [PATCH] HID: uhid: prevent uhid_char_write() under KERNEL_DS Eric Biggers
2018-11-14 18:14 ` Dmitry Torokhov
2018-11-14 18:18 ` Jann Horn
2018-11-14 21:54 ` Eric Biggers
2018-11-14 21:55 ` [PATCH v2] HID: uhid: forbid UHID_CREATE under KERNEL_DS or elevated privileges Eric Biggers
2018-11-14 22:04 ` Jann Horn
2018-11-14 22:28 ` Dmitry Torokhov
2018-11-14 22:37 ` Jann Horn
2018-11-14 22:46 ` Dmitry Torokhov
2018-11-15 0:39 ` Andy Lutomirski
2018-11-14 23:00 ` Eric Biggers
2018-11-14 23:20 ` Dmitry Torokhov
2018-11-15 8:14 ` Benjamin Tissoires
2018-11-15 12:06 ` David Herrmann
2018-11-15 14:50 ` Andy Lutomirski
2018-11-15 12:09 ` David Herrmann
2018-11-15 14:49 ` Andy Lutomirski
2018-11-19 12:52 ` Jiri Kosina [this message]
2018-11-19 13:21 ` David Herrmann
2018-11-19 13:26 ` Jiri Kosina
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