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Date:   Mon, 11 Dec 2023 21:00:16 +0100
From:   Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
To:     Andrei Vagin <avagin@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Amir Goldstein <amir73il@gmail.com>,
        Alexander Mikhalitsyn <alexander@mihalicyn.com>
Subject: Re: [PATCH 2/2] selftests/overlayfs: verify device and inode
 numbers in /proc/pid/maps
Message-Id: <20231211210016.c6bb5b6d8c88bfcc6e33c880@canonical.com>
In-Reply-To: <20231211193048.580691-2-avagin@google.com>
References: <20231211193048.580691-1-avagin@google.com>
        <20231211193048.580691-2-avagin@google.com>
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On Mon, 11 Dec 2023 11:30:48 -0800
Andrei Vagin <avagin@google.com> wrote:

> When mapping a file on overlayfs, the file stored in ->vm_file is a
> backing file whose f_inode is on the underlying filesystem. We need to
> verify that /proc/pid/maps contains numbers of the overlayfs file, but
> not its backing file.
> 
> Cc: Amir Goldstein <amir73il@gmail.com>
> Cc: Alexander Mikhalitsyn <alexander@mihalicyn.com>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>

> Signed-off-by: Andrei Vagin <avagin@google.com>
> ---
>  tools/testing/selftests/Makefile              |   1 +
>  .../filesystems/overlayfs/.gitignore          |   2 +
>  .../selftests/filesystems/overlayfs/Makefile  |   7 +
>  .../filesystems/overlayfs/dev_in_maps.c       | 182 ++++++++++++++++++
>  .../selftests/filesystems/overlayfs/log.h     |  26 +++
>  5 files changed, 218 insertions(+)
>  create mode 100644 tools/testing/selftests/filesystems/overlayfs/.gitignore
>  create mode 100644 tools/testing/selftests/filesystems/overlayfs/Makefile
>  create mode 100644 tools/testing/selftests/filesystems/overlayfs/dev_in_maps.c
>  create mode 100644 tools/testing/selftests/filesystems/overlayfs/log.h
> 
> diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
> index 3b2061d1c1a5..0939a40abb28 100644
> --- a/tools/testing/selftests/Makefile
> +++ b/tools/testing/selftests/Makefile
> @@ -26,6 +26,7 @@ TARGETS += filesystems
>  TARGETS += filesystems/binderfs
>  TARGETS += filesystems/epoll
>  TARGETS += filesystems/fat
> +TARGETS += filesystems/overlayfs
>  TARGETS += firmware
>  TARGETS += fpu
>  TARGETS += ftrace
> diff --git a/tools/testing/selftests/filesystems/overlayfs/.gitignore b/tools/testing/selftests/filesystems/overlayfs/.gitignore
> new file mode 100644
> index 000000000000..52ae618fdd98
> --- /dev/null
> +++ b/tools/testing/selftests/filesystems/overlayfs/.gitignore
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +dev_in_maps
> diff --git a/tools/testing/selftests/filesystems/overlayfs/Makefile b/tools/testing/selftests/filesystems/overlayfs/Makefile
> new file mode 100644
> index 000000000000..56b2b48a765b
> --- /dev/null
> +++ b/tools/testing/selftests/filesystems/overlayfs/Makefile
> @@ -0,0 +1,7 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +TEST_GEN_PROGS := dev_in_maps
> +
> +CFLAGS := -Wall -Werror
> +
> +include ../../lib.mk
> diff --git a/tools/testing/selftests/filesystems/overlayfs/dev_in_maps.c b/tools/testing/selftests/filesystems/overlayfs/dev_in_maps.c
> new file mode 100644
> index 000000000000..08497c2e10a3
> --- /dev/null
> +++ b/tools/testing/selftests/filesystems/overlayfs/dev_in_maps.c
> @@ -0,0 +1,182 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define _GNU_SOURCE
> +
> +#include <inttypes.h>
> +#include <unistd.h>
> +#include <stdio.h>
> +
> +#include <linux/unistd.h>
> +#include <linux/types.h>
> +#include <linux/mount.h>
> +#include <sys/syscall.h>
> +#include <sys/stat.h>
> +#include <sys/mount.h>
> +#include <sys/mman.h>
> +#include <sched.h>
> +#include <fcntl.h>
> +
> +#include "../../kselftest.h"
> +#include "log.h"
> +
> +static int sys_fsopen(const char *fsname, unsigned int flags)
> +{
> +	return syscall(__NR_fsopen, fsname, flags);
> +}
> +
> +static int sys_fsconfig(int fd, unsigned int cmd, const char *key, const char *value, int aux)
> +{
> +	return syscall(__NR_fsconfig, fd, cmd, key, value, aux);
> +}
> +
> +static int sys_fsmount(int fd, unsigned int flags, unsigned int attr_flags)
> +{
> +	return syscall(__NR_fsmount, fd, flags, attr_flags);
> +}
> +
> +static int sys_move_mount(int from_dfd, const char *from_pathname,
> +			  int to_dfd, const char *to_pathname,
> +			  unsigned int flags)
> +{
> +	return syscall(__NR_move_mount, from_dfd, from_pathname, to_dfd, to_pathname, flags);
> +}
> +
> +static long get_file_dev_and_inode(void *addr, struct statx *stx)
> +{
> +	char buf[4096];
> +	FILE *mapf;
> +
> +	mapf = fopen("/proc/self/maps", "r");
> +	if (mapf == NULL)
> +		return pr_perror("fopen(/proc/self/maps)");
> +
> +	while (fgets(buf, sizeof(buf), mapf)) {
> +		unsigned long start, end;
> +		uint32_t maj, min;
> +		__u64 ino;
> +
> +		if (sscanf(buf, "%lx-%lx %*s %*s %x:%x %llx",
> +				&start, &end, &maj, &min, &ino) != 5)
> +			return pr_perror("unable to parse: %s", buf);
> +		if (start == (unsigned long)addr) {
> +			stx->stx_dev_major = maj;
> +			stx->stx_dev_minor = min;
> +			stx->stx_ino = ino;
> +			return 0;
> +		}
> +	}
> +
> +	return pr_err("unable to find the mapping");
> +}
> +
> +static int ovl_mount(void)
> +{
> +	int tmpfs, fsfd, ovl;
> +
> +	fsfd = sys_fsopen("tmpfs", 0);
> +	if (fsfd == -1)
> +		return pr_perror("fsopen(tmpfs)");
> +
> +	if (sys_fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) == -1)
> +		return pr_perror("FSCONFIG_CMD_CREATE");
> +
> +	tmpfs = sys_fsmount(fsfd, 0, 0);
> +	if (tmpfs == -1)
> +		return pr_perror("fsmount");
> +
> +	close(fsfd);
> +
> +	/* overlayfs can't be constructed on top of a detached mount. */
> +	if (sys_move_mount(tmpfs, "", AT_FDCWD, "/tmp", MOVE_MOUNT_F_EMPTY_PATH))
> +		return pr_perror("move_mount");
> +	close(tmpfs);
> +
> +	if (mkdir("/tmp/w", 0755) == -1 ||
> +	    mkdir("/tmp/u", 0755) == -1 ||
> +	    mkdir("/tmp/l", 0755) == -1)
> +		return pr_perror("mkdir");
> +
> +	fsfd = sys_fsopen("overlay", 0);
> +	if (fsfd == -1)
> +		return pr_perror("fsopen(overlay)");
> +	if (sys_fsconfig(fsfd, FSCONFIG_SET_STRING, "source", "test", 0) == -1 ||
> +	    sys_fsconfig(fsfd, FSCONFIG_SET_STRING, "lowerdir", "/tmp/l", 0) == -1 ||
> +	    sys_fsconfig(fsfd, FSCONFIG_SET_STRING, "upperdir", "/tmp/u", 0) == -1 ||
> +	    sys_fsconfig(fsfd, FSCONFIG_SET_STRING, "workdir", "/tmp/w", 0) == -1)
> +		return pr_perror("fsconfig");
> +	if (sys_fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) == -1)
> +		return pr_perror("fsconfig");
> +	ovl = sys_fsmount(fsfd, 0, 0);
> +	if (ovl == -1)
> +		return pr_perror("fsmount");
> +
> +	return ovl;
> +}
> +
> +/*
> + * Check that the file device and inode shown in /proc/pid/maps match values
> + * returned by stat(2).
> + */
> +static int test(void)
> +{
> +	struct statx stx, mstx;
> +	int ovl, fd;
> +	void *addr;
> +
> +	ovl = ovl_mount();
> +	if (ovl == -1)
> +		return -1;
> +
> +	fd = openat(ovl, "test", O_RDWR | O_CREAT, 0644);
> +	if (fd == -1)
> +		return pr_perror("openat");
> +
> +	addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, 0);
> +	if (addr == MAP_FAILED)
> +		return pr_perror("mmap");
> +
> +	if (get_file_dev_and_inode(addr, &mstx))
> +		return -1;
> +	if (statx(fd, "", AT_EMPTY_PATH | AT_STATX_SYNC_AS_STAT, STATX_INO, &stx))
> +		return pr_perror("statx");
> +
> +	if (stx.stx_dev_major != mstx.stx_dev_major ||
> +	    stx.stx_dev_minor != mstx.stx_dev_minor ||
> +	    stx.stx_ino != mstx.stx_ino)
> +		return pr_fail("unmatched dev:ino %x:%x:%llx (expected %x:%x:%llx)\n",
> +			mstx.stx_dev_major, mstx.stx_dev_minor, mstx.stx_ino,
> +			stx.stx_dev_major, stx.stx_dev_minor, stx.stx_ino);
> +
> +	ksft_test_result_pass("devices are matched\n");
> +	return 0;
> +}
> +
> +int main(int argc, char **argv)
> +{
> +	int fsfd;
> +
> +	fsfd = sys_fsopen("overlay", 0);
> +	if (fsfd == -1) {
> +		ksft_test_result_skip("unable to create overlay mount\n");
> +		return 1;
> +	}
> +	close(fsfd);
> +
> +	/* Create a new mount namespace to not care about cleaning test mounts. */
> +	if (unshare(CLONE_NEWNS) == -1) {
> +		ksft_test_result_skip("unable to create a new mount namespace\n");
> +		return 1;
> +	}
> +
> +	if (mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL) == -1) {
> +		pr_perror("mount");
> +		return 1;
> +	}
> +
> +	ksft_set_plan(1);
> +
> +	if (test())
> +		return 1;
> +
> +	ksft_exit_pass();
> +	return 0;
> +}
> diff --git a/tools/testing/selftests/filesystems/overlayfs/log.h b/tools/testing/selftests/filesystems/overlayfs/log.h
> new file mode 100644
> index 000000000000..db64df2a8483
> --- /dev/null
> +++ b/tools/testing/selftests/filesystems/overlayfs/log.h
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef __SELFTEST_TIMENS_LOG_H__
> +#define __SELFTEST_TIMENS_LOG_H__
> +
> +#define pr_msg(fmt, lvl, ...)						\
> +	ksft_print_msg("[%s] (%s:%d)\t" fmt "\n",			\
> +			lvl, __FILE__, __LINE__, ##__VA_ARGS__)
> +
> +#define pr_p(func, fmt, ...)	func(fmt ": %m", ##__VA_ARGS__)
> +
> +#define pr_err(fmt, ...)						\
> +	({								\
> +		ksft_test_result_error(fmt "\n", ##__VA_ARGS__);		\
> +		-1;							\
> +	})
> +
> +#define pr_fail(fmt, ...)					\
> +	({							\
> +		ksft_test_result_fail(fmt, ##__VA_ARGS__);	\
> +		-1;						\
> +	})
> +
> +#define pr_perror(fmt, ...)	pr_p(pr_err, fmt, ##__VA_ARGS__)
> +
> +#endif
> -- 
> 2.43.0.472.g3155946c3a-goog
> 


-- 
Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>