[LTP] [PATCH 3/3] Add test for CVE 2018-13405

[Richard Palethorpe]

Hello Martin,

Martin Doucha <mdoucha@suse.cz> writes:

> Signed-off-by: Martin Doucha <mdoucha@suse.cz>
> ---
>  runtest/cve                                |   1 +
>  runtest/syscalls                           |   1 +
>  testcases/kernel/syscalls/creat/.gitignore |   1 +
>  testcases/kernel/syscalls/creat/creat09.c  | 115 +++++++++++++++++++++
>  4 files changed, 118 insertions(+)
>  create mode 100644 testcases/kernel/syscalls/creat/creat09.c
>
> diff --git a/runtest/cve b/runtest/cve
> index c27f58d8d..42c8eedbe 100644
> --- a/runtest/cve
> +++ b/runtest/cve
> @@ -55,6 +55,7 @@ cve-2018-1000001 realpath01
>  cve-2018-1000199 ptrace08
>  cve-2018-1000204 ioctl_sg01
>  cve-2018-12896 timer_settime03
> +cve-2018-13405 creat09
>  cve-2018-18445 bpf_prog04
>  cve-2018-18559 bind06
>  cve-2018-18955 userns08
> diff --git a/runtest/syscalls b/runtest/syscalls
> index 9af5aa5c0..161794f2a 100644
> --- a/runtest/syscalls
> +++ b/runtest/syscalls
> @@ -136,6 +136,7 @@ creat05 creat05
>  creat06 creat06
>  creat07 creat07
>  creat08 creat08
> +creat09 creat09
>  
>  delete_module01 delete_module01
>  delete_module02 delete_module02
> diff --git a/testcases/kernel/syscalls/creat/.gitignore b/testcases/kernel/syscalls/creat/.gitignore
> index a39e63590..caafc02b6 100644
> --- a/testcases/kernel/syscalls/creat/.gitignore
> +++ b/testcases/kernel/syscalls/creat/.gitignore
> @@ -6,3 +6,4 @@
>  /creat07
>  /creat07_child
>  /creat08
> +/creat09
> diff --git a/testcases/kernel/syscalls/creat/creat09.c b/testcases/kernel/syscalls/creat/creat09.c
> new file mode 100644
> index 000000000..6255d8784
> --- /dev/null
> +++ b/testcases/kernel/syscalls/creat/creat09.c
> @@ -0,0 +1,115 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (c) 2021 SUSE LLC <mdoucha@suse.cz>
> + *
> + * CVE-2018-13405
> + *
> + * Check for possible privilege escalation through creating files with setgid
> + * bit set inside a setgid directory owned by a group which the user does not
> + * belong to. Fixed in:
> + *
> + *  commit 0fa3ecd87848c9c93c2c828ef4c3a8ca36ce46c7
> + *  Author: Linus Torvalds <torvalds@linux-foundation.org>
> + *  Date:   Tue Jul 3 17:10:19 2018 -0700
> + *
> + *  Fix up non-directory creation in SGID directories
> + */

Very interesting bug! FYI, I noticed this code was changed again
recently to make it mount/user namespace aware. Which then reminds me of
userns08.

> +
> +#include <stdlib.h>
> +#include <sys/types.h>
> +#include <pwd.h>
> +#include "tst_test.h"
> +
> +#define MODE_RWX        0777
> +#define MODE_SGID       (S_ISGID|0777)
> +
> +#define WORKDIR		"testdir"
> +#define CREAT_FILE	WORKDIR "/creat.tmp"
> +#define OPEN_FILE	WORKDIR "/open.tmp"
> +
> +static uid_t orig_uid;
> +static gid_t bin_gid;
> +static int fd = -1;
> +
> +static void setup(void)
> +{
> +	struct stat buf;
> +	struct passwd *ltpuser = SAFE_GETPWNAM("nobody");
> +	struct group *ltpgroup = SAFE_GETGRNAM("bin");

These might not exist on some systems. I think you can just pick
arbitrary UID/GID numbers instead. No need to check the user/group
databases.

> +
> +	orig_uid = getuid();
> +	bin_gid = ltpgroup->gr_gid;
> +
> +	/* Create directories and set permissions */
> +	SAFE_MKDIR(WORKDIR, MODE_RWX);
> +	SAFE_CHOWN(WORKDIR, ltpuser->pw_uid, bin_gid);
> +	SAFE_CHMOD(WORKDIR, MODE_SGID);
> +	SAFE_STAT(WORKDIR, &buf);
> +
> +	if (!(buf.st_mode & S_ISGID))
> +		tst_brk(TBROK, "%s: Setgid bit not set", WORKDIR);
> +
> +	if (buf.st_gid != bin_gid) {
> +		tst_brk(TBROK, "%s: Incorrect group, %u != %u", WORKDIR,
> +			buf.st_gid, bin_gid);
> +	}
> +
> +	/* Switch user */
> +	ltpgroup = SAFE_GETGRNAM_FALLBACK("nobody", "nogroup");
> +	SAFE_SETGID(ltpgroup->gr_gid);
> +	SAFE_SETREUID(-1, ltpuser->pw_uid);
> +}
> +
> +static void file_test(const char *name, gid_t gid)

gid is always set to bin_gid.

> +{
> +	struct stat buf;
> +
> +	SAFE_STAT(name, &buf);
> +
> +	if (buf.st_gid != gid) {
> +		tst_res(TFAIL, "%s: Incorrect group, %u != %u", name,
> +			buf.st_gid, gid);
> +	} else {
> +		tst_res(TPASS, "%s: Owned by correct group", name);
> +	}
> +
> +	if (buf.st_mode & S_ISGID)
> +		tst_res(TFAIL, "%s: Setgid bit is set", name);
> +	else
> +		tst_res(TPASS, "%s: Setgid bit not set", name);
> +}
> +
> +static void run(void)
> +{
> +	fd = SAFE_CREAT(CREAT_FILE, MODE_SGID);
> +	SAFE_CLOSE(fd);
> +	file_test(CREAT_FILE, bin_gid);
> +
> +	fd = SAFE_OPEN(OPEN_FILE, O_CREAT | O_EXCL | O_RDWR, MODE_SGID);
> +	file_test(OPEN_FILE, bin_gid);
> +	SAFE_CLOSE(fd);
> +
> +	/* Cleanup between loops */
> +	tst_purge_dir(WORKDIR);
> +}
> +
> +static void cleanup(void)
> +{
> +	SAFE_SETREUID(-1, orig_uid);

Why are you doing this? I am assuming the temp dir will be deleted by
the parent process.

> +
> +	if (fd >= 0)
> +		SAFE_CLOSE(fd);
> +}
> +
> +static struct tst_test test = {
> +	.test_all = run,
> +	.setup = setup,
> +	.cleanup = cleanup,
> +	.needs_root = 1,
> +	.needs_tmpdir = 1,
> +	.tags = (const struct tst_tag[]) {
> +		{"linux-git", "0fa3ecd87848"},
> +		{"CVE", "2018-13405"},
> +		{}
> +	},
> +};
> -- 
> 2.32.0


-- 
Thank you,
Richard.