Re: [PATCH liburing] a test for CVE-2020-29373 (AF_UNIX path resolution)

[Pavel Begunkov <asml.silence@gmail.com>]

On 12/02/2021 21:02, Pavel Begunkov wrote:
> Add a regression test for CVE-2020-29373 where io-wq do path resolution
> issuing sendmsg, but doesn't have proper fs set up.

Jens, what about licenses? The original test is GPLv2

> 
> Reported-by: Petr Vorel <pvorel@suse.cz>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  test/Makefile         |   2 +
>  test/sendmsg_fs_cve.c | 193 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 195 insertions(+)
>  create mode 100644 test/sendmsg_fs_cve.c
> 
> diff --git a/test/Makefile b/test/Makefile
> index 157ff95..7751eff 100644
> --- a/test/Makefile
> +++ b/test/Makefile
> @@ -111,6 +111,7 @@ test_targets += \
>  	timeout-overflow \
>  	unlink \
>  	wakeup-hang \
> +	sendmsg_fs_cve \
>  	# EOL
>  
>  all_targets += $(test_targets)
> @@ -238,6 +239,7 @@ test_srcs := \
>  	timeout.c \
>  	unlink.c \
>  	wakeup-hang.c \
> +	sendmsg_fs_cve.c \
>  	# EOL
>  
>  test_objs := $(patsubst %.c,%.ol,$(patsubst %.cc,%.ol,$(test_srcs)))
> diff --git a/test/sendmsg_fs_cve.c b/test/sendmsg_fs_cve.c
> new file mode 100644
> index 0000000..85f271b
> --- /dev/null
> +++ b/test/sendmsg_fs_cve.c
> @@ -0,0 +1,193 @@
> +/*
> + * repro-CVE-2020-29373 -- Reproducer for CVE-2020-29373.
> + *
> + * Copyright (c) 2021 SUSE
> + * Author: Nicolai Stange <nstange@suse.de>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <unistd.h>
> +#include <syscall.h>
> +#include <stdio.h>
> +#include <sys/mman.h>
> +#include <sys/socket.h>
> +#include <sys/un.h>
> +#include <fcntl.h>
> +#include <errno.h>
> +#include <inttypes.h>
> +#include <stdlib.h>
> +#include <sys/types.h>
> +#include <sys/wait.h>
> +#include "liburing.h"
> +
> +/*
> + * This attempts to make the kernel issue a sendmsg() to
> + * path from io_uring's async io_sq_wq_submit_work().
> + *
> + * Unfortunately, IOSQE_ASYNC is available only from kernel version
> + * 5.6 onwards. To still force io_uring to process the request
> + * asynchronously from io_sq_wq_submit_work(), queue a couple of
> + * auxiliary requests all failing with EAGAIN before. This is
> + * implemented by writing repeatedly to an auxiliary O_NONBLOCK
> + * AF_UNIX socketpair with a small SO_SNDBUF.
> + */
> +static int try_sendmsg_async(const char * const path)
> +{
> +	int snd_sock, r;
> +	struct io_uring ring;
> +	char sbuf[16] = {};
> +	struct iovec siov = { .iov_base = &sbuf, .iov_len = sizeof(sbuf) };
> +	struct sockaddr_un addr = {};
> +	struct msghdr msg = {
> +		.msg_name = &addr,
> +		.msg_namelen = sizeof(addr),
> +		.msg_iov = &siov,
> +		.msg_iovlen = 1,
> +	};
> +	struct io_uring_cqe *cqe;
> +	struct io_uring_sqe *sqe;
> +
> +	snd_sock = socket(AF_UNIX, SOCK_DGRAM, 0);
> +	if (snd_sock < 0) {
> +		perror("socket(AF_UNIX)");
> +		return -1;
> +	}
> +
> +	addr.sun_family = AF_UNIX;
> +	strcpy(addr.sun_path, path);
> +
> +	r = io_uring_queue_init(512, &ring, 0);
> +	if (r < 0) {
> +		fprintf(stderr, "ring setup failed: %d\n", r);
> +		goto close_iour;
> +	}
> +
> +	sqe = io_uring_get_sqe(&ring);
> +	if (!sqe) {
> +		fprintf(stderr, "get sqe failed\n");
> +		r = -EFAULT;
> +		goto close_iour;
> +	}
> +
> +	/* the actual one supposed to fail with -ENOENT. */
> +	io_uring_prep_sendmsg(sqe, snd_sock, &msg, 0);
> +	sqe->flags = IOSQE_ASYNC;
> +	sqe->user_data = 255;
> +
> +	r = io_uring_submit(&ring);
> +	if (r != 1) {
> +		fprintf(stderr, "sqe submit failed: %d\n", r);
> +		r = -EFAULT;
> +		goto close_iour;
> +	}
> +
> +	r = io_uring_wait_cqe(&ring, &cqe);
> +	if (r < 0) {
> +		fprintf(stderr, "wait completion %d\n", r);
> +		r = -EFAULT;
> +		goto close_iour;
> +	}
> +	if (cqe->user_data != 255) {
> +		fprintf(stderr, "user data %d\n", r);
> +		r = -EFAULT;
> +		goto close_iour;
> +	}
> +	if (cqe->res != -ENOENT) {
> +		r = 3;
> +		fprintf(stderr,
> +			"error: cqe %i: res=%i, but expected -ENOENT\n",
> +			(int)cqe->user_data, (int)cqe->res);
> +	}
> +	io_uring_cqe_seen(&ring, cqe);
> +
> +close_iour:
> +	io_uring_queue_exit(&ring);
> +	close(snd_sock);
> +	return r;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	int r;
> +	char tmpdir[] = "/tmp/tmp.XXXXXX";
> +	int rcv_sock;
> +	struct sockaddr_un addr = {};
> +	pid_t c;
> +	int wstatus;
> +
> +	if (!mkdtemp(tmpdir)) {
> +		perror("mkdtemp()");
> +		return 1;
> +	}
> +
> +	rcv_sock = socket(AF_UNIX, SOCK_DGRAM, 0);
> +	if (rcv_sock < 0) {
> +		perror("socket(AF_UNIX)");
> +		r = 1;
> +		goto rmtmpdir;
> +	}
> +
> +	addr.sun_family = AF_UNIX;
> +	snprintf(addr.sun_path, sizeof(addr.sun_path), "%s/sock", tmpdir);
> +
> +	r = bind(rcv_sock, (struct sockaddr *)&addr,
> +		 sizeof(addr));
> +	if (r < 0) {
> +		perror("bind()");
> +		close(rcv_sock);
> +		r = 1;
> +		goto rmtmpdir;
> +	}
> +
> +	c = fork();
> +	if (!c) {
> +		close(rcv_sock);
> +
> +		if (chroot(tmpdir)) {
> +			perror("chroot()");
> +			return 1;
> +		}
> +
> +		r = try_sendmsg_async(addr.sun_path);
> +		if (r < 0) {
> +			/* system call failure */
> +			r = 1;
> +		} else if (r) {
> +			/* test case failure */
> +			r += 1;
> +		}
> +		return r;
> +	}
> +
> +	if (waitpid(c, &wstatus, 0) == (pid_t)-1) {
> +		perror("waitpid()");
> +		r = 1;
> +		goto rmsock;
> +	}
> +	if (!WIFEXITED(wstatus)) {
> +		fprintf(stderr, "child got terminated\n");
> +		r = 1;
> +		goto rmsock;
> +	}
> +	r = WEXITSTATUS(wstatus);
> +	if (r)
> +		fprintf(stderr, "error: Test failed\n");
> +rmsock:
> +	close(rcv_sock);
> +	unlink(addr.sun_path);
> +rmtmpdir:
> +	rmdir(tmpdir);
> +	return r;
> +}
> 

-- 
Pavel Begunkov