From: Eric Biggers <ebiggers@kernel.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Matthew Wilcox <willy@infradead.org>,
David Laight <David.Laight@aculab.com>,
Christoph Hellwig <hch@lst.de>,
David Hildenbrand <david@redhat.com>,
Greg KH <gregkh@linuxfoundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
"kernel-team@android.com" <kernel-team@android.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jens Axboe <axboe@kernel.dk>, Arnd Bergmann <arnd@arndb.de>,
David Howells <dhowells@redhat.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
"linux-parisc@vger.kernel.org" <linux-parisc@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
"sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-aio@kvack.org" <linux-aio@kvack.org>,
"io-uring@vger.kernel.org" <io-uring@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"keyrings@vger.kernel.org" <keyrings@vger.kernel.org>,
"linux-security-module@vger.kernel.org"
<linux-security-module@vger.kernel.org>
Subject: Re: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c"
Date: Thu, 22 Oct 2020 13:59:32 -0700 [thread overview]
Message-ID: <20201022205932.GB3613750@gmail.com> (raw)
In-Reply-To: <CAKwvOdnq-yYLcF_coo=jMV-RH-SkuNp_kMB+KCBF5cz3PwiB8g@mail.gmail.com>
On Thu, Oct 22, 2020 at 10:00:44AM -0700, Nick Desaulniers wrote:
> On Thu, Oct 22, 2020 at 9:40 AM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Thu, Oct 22, 2020 at 04:35:17PM +0000, David Laight wrote:
> > > Wait...
> > > readv(2) defines:
> > > ssize_t readv(int fd, const struct iovec *iov, int iovcnt);
> >
> > It doesn't really matter what the manpage says. What does the AOSP
> > libc header say?
>
> Same: https://android.googlesource.com/platform/bionic/+/refs/heads/master/libc/include/sys/uio.h#38
>
> Theoretically someone could bypass libc to make a system call, right?
>
> >
> > > But the syscall is defined as:
> > >
> > > SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
> > > unsigned long, vlen)
> > > {
> > > return do_readv(fd, vec, vlen, 0);
> > > }
> >
>
FWIW, glibc makes the readv() syscall assuming that fd and vlen are 'int' as
well. So this problem isn't specific to Android's libc.
From objdump -d /lib/x86_64-linux-gnu/libc.so.6:
00000000000f4db0 <readv@@GLIBC_2.2.5>:
f4db0: 64 8b 04 25 18 00 00 mov %fs:0x18,%eax
f4db7: 00
f4db8: 85 c0 test %eax,%eax
f4dba: 75 14 jne f4dd0 <readv@@GLIBC_2.2.5+0x20>
f4dbc: b8 13 00 00 00 mov $0x13,%eax
f4dc1: 0f 05 syscall
...
There's some code for pthread cancellation, but no zeroing of the upper half of
the fd and vlen arguments, which are in %edi and %edx respectively. But the
glibc function prototype uses 'int' for them, not 'unsigned long'
'ssize_t readv(int fd, const struct iovec *iov, int iovcnt);'.
So the high halves of the fd and iovcnt registers can contain garbage. Or at
least that's what gcc (9.3.0) and clang (9.0.1) assume; they both compile the
following
void g(unsigned int x);
void f(unsigned long x)
{
g(x);
}
into f() making a tail call to g(), without zeroing the top half of %rdi.
Also note the following program succeeds on Linux 5.9 on x86_64. On kernels
that have this bug, it should fail. (I couldn't get it to actually fail, so it
must depend on the compiler and/or the kernel config...)
#include <fcntl.h>
#include <stdio.h>
#include <sys/syscall.h>
#include <sys/uio.h>
#include <unistd.h>
int main()
{
int fd = open("/dev/zero", O_RDONLY);
char buf[1000];
struct iovec iov = { .iov_base = buf, .iov_len = sizeof(buf) };
long ret;
ret = syscall(__NR_readv, fd, &iov, 0x100000001);
if (ret < 0)
perror("readv failed");
else
printf("read %ld bytes\n", ret);
}
I think the right fix is to change the readv() (and writev(), etc.) syscalls to
take 'unsigned int' rather than 'unsigned long', as that is what the users are
assuming...
- Eric
next prev parent reply other threads:[~2020-10-22 20:59 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-25 4:51 let import_iovec deal with compat_iovecs as well v4 Christoph Hellwig
2020-09-25 4:51 ` [PATCH 1/9] compat.h: fix a spelling error in <linux/compat.h> Christoph Hellwig
2020-09-25 4:51 ` [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c Christoph Hellwig
2020-10-21 16:13 ` Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c" Greg KH
2020-10-21 20:59 ` David Laight
2020-10-21 23:39 ` Al Viro
2020-10-22 8:26 ` Greg KH
2020-10-22 8:35 ` David Hildenbrand
2020-10-22 8:40 ` David Laight
2020-10-22 8:48 ` David Hildenbrand
2020-10-22 9:01 ` Greg KH
2020-10-22 9:06 ` David Laight
2020-10-22 9:19 ` David Hildenbrand
2020-10-22 9:25 ` David Hildenbrand
2020-10-22 9:32 ` David Laight
2020-10-22 9:36 ` David Hildenbrand
2020-10-22 10:48 ` Greg KH
2020-10-22 12:18 ` Greg KH
2020-10-22 12:42 ` David Hildenbrand
2020-10-22 12:57 ` Greg KH
2020-10-22 13:50 ` Greg KH
[not found] ` <CAK8P3a1B7OVdyzW0-97JwzZiwp0D0fnSfyete16QTvPp_1m07A@mail.gmail.com>
2020-10-22 14:40 ` Greg KH
2020-10-22 16:15 ` David Laight
2020-10-23 12:46 ` David Laight
2020-10-23 13:09 ` David Hildenbrand
2020-10-23 14:33 ` David Hildenbrand
2020-10-23 14:39 ` David Laight
2020-10-23 14:47 ` 'Greg KH'
2020-10-23 16:33 ` David Hildenbrand
2020-11-02 9:06 ` David Laight
2020-11-02 13:52 ` 'Greg KH'
2020-11-02 18:23 ` David Laight
2020-10-23 17:58 ` Al Viro
2020-10-23 18:27 ` Segher Boessenkool
2020-10-23 21:28 ` David Laight
2020-10-24 17:29 ` Segher Boessenkool
2020-10-24 21:12 ` David Laight
[not found] ` <CAK8P3a1n+b8hOMhNQSDzgic03dyXbmpccfTJ3C1bGKvzsgMXbg@mail.gmail.com>
2020-10-23 13:28 ` David Laight
2020-10-22 13:23 ` Christoph Hellwig
2020-10-22 16:35 ` David Laight
2020-10-22 16:40 ` Matthew Wilcox
2020-10-22 16:50 ` David Laight
2020-10-22 17:00 ` Nick Desaulniers
2020-10-22 20:59 ` Eric Biggers [this message]
2020-10-22 21:28 ` Al Viro
2020-10-22 18:19 ` Al Viro
2020-10-22 17:54 ` Nick Desaulniers
[not found] ` <CAK8P3a3LjG+ZvmQrkb9zpgov8xBkQQWrkHBPgjfYSqBKGrwT4w@mail.gmail.com>
2020-10-22 19:04 ` Nick Desaulniers
2020-10-22 19:24 ` Al Viro
2020-10-22 19:27 ` Al Viro
2020-10-22 20:06 ` Al Viro
2020-10-22 20:09 ` Al Viro
2020-10-22 20:11 ` Nick Desaulniers
2020-10-22 22:07 ` David Laight
2020-10-23 13:12 ` David Hildenbrand
2020-10-22 22:04 ` David Laight
2020-10-22 9:28 ` David Laight
2020-10-22 9:02 ` David Laight
2020-09-25 4:51 ` [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Christoph Hellwig
2020-09-25 4:51 ` [PATCH 4/9] iov_iter: transparently handle compat iovecs in import_iovec Christoph Hellwig
2020-09-25 4:51 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-25 4:51 ` [PATCH 6/9] fs: remove the compat readv/writev syscalls Christoph Hellwig
2020-09-25 4:51 ` [PATCH 7/9] fs: remove compat_sys_vmsplice Christoph Hellwig
2020-09-25 4:51 ` [PATCH 8/9] mm: remove compat_process_vm_{readv,writev} Christoph Hellwig
2020-09-25 4:51 ` [PATCH 9/9] security/keys: remove compat_keyctl_instantiate_key_iov Christoph Hellwig
2020-09-25 15:23 ` let import_iovec deal with compat_iovecs as well v4 Al Viro
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=20201022205932.GB3613750@gmail.com \
--to=ebiggers@kernel.org \
--cc=David.Laight@aculab.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=axboe@kernel.dk \
--cc=david@redhat.com \
--cc=dhowells@redhat.com \
--cc=gregkh@linuxfoundation.org \
--cc=hch@lst.de \
--cc=io-uring@vger.kernel.org \
--cc=kernel-team@android.com \
--cc=keyrings@vger.kernel.org \
--cc=linux-aio@kvack.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-parisc@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=linux-scsi@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=ndesaulniers@google.com \
--cc=netdev@vger.kernel.org \
--cc=sparclinux@vger.kernel.org \
--cc=viro@zeniv.linux.org.uk \
--cc=willy@infradead.org \
/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).