From: Matthew Wilcox <willy@infradead.org>
To: syzbot <syzbot+3de312463756f656b47d@syzkaller.appspotmail.com>
Cc: allison@lohutok.net, andreyknvl@google.com, cai@lca.pw,
gregkh@linuxfoundation.org, keescook@chromium.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com,
tglx@linutronix.de, Jiri Kosina <jkosina@suse.cz>
Subject: Re: BUG: bad usercopy in hidraw_ioctl
Date: Wed, 7 Aug 2019 12:58:21 -0700 [thread overview]
Message-ID: <20190807195821.GD5482@bombadil.infradead.org> (raw)
In-Reply-To: <000000000000ce6527058f8bf0d0@google.com>
On Wed, Aug 07, 2019 at 12:28:06PM -0700, syzbot wrote:
> usercopy: Kernel memory exposure attempt detected from wrapped address
> (offset 0, size 0)!
> ------------[ cut here ]------------
> kernel BUG at mm/usercopy.c:98!
This report is confusing because the arguments to usercopy_abort() are wrong.
/* Reject if object wraps past end of memory. */
if (ptr + n < ptr)
usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n);
ptr + n is not 'size', it's what wrapped. I don't know what 'offset'
should be set to, but 'size' should be 'n'. Presumably we don't want to
report 'ptr' because it'll leak a kernel address ... reporting 'n' will
leak a range for a kernel address, but I think that's OK? Admittedly an
attacker can pass in various values for 'n', but it'll be quite noisy
and leave a trace in the kernel logs for forensics to find afterwards.
> Call Trace:
> check_bogus_address mm/usercopy.c:151 [inline]
> __check_object_size mm/usercopy.c:260 [inline]
> __check_object_size.cold+0xb2/0xba mm/usercopy.c:250
> check_object_size include/linux/thread_info.h:119 [inline]
> check_copy_size include/linux/thread_info.h:150 [inline]
> copy_to_user include/linux/uaccess.h:151 [inline]
> hidraw_ioctl+0x38c/0xae0 drivers/hid/hidraw.c:392
The root problem would appear to be:
else if (copy_to_user(user_arg + offsetof(
struct hidraw_report_descriptor,
value[0]),
dev->hid->rdesc,
min(dev->hid->rsize, len)))
That 'min' should surely be a 'max'?
Jiri, this looks like it was your code back in 2007.
next prev parent reply other threads:[~2019-08-07 19:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-07 19:28 BUG: bad usercopy in hidraw_ioctl syzbot
2019-08-07 19:58 ` Matthew Wilcox [this message]
2019-08-08 1:49 ` Al Viro
2019-08-08 20:41 ` Kees Cook
2019-08-08 20:27 ` Kees Cook
2019-08-21 17:00 ` Andrey Konovalov
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