Merge branch 'work.openat2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull openat2 support from Al Viro:
 "This is the openat2() series from Aleksa Sarai.

  I'm afraid that the rest of namei stuff will have to wait - it got
  zero review the last time I'd posted #work.namei, and there had been a
  leak in the posted series I'd caught only last weekend. I was going to
  repost it on Monday, but the window opened and the odds of getting any
  review during that... Oh, well.

  Anyway, openat2 part should be ready; that _did_ get sane amount of
  review and public testing, so here it comes"

From Aleksa's description of the series:
 "For a very long time, extending openat(2) with new features has been
  incredibly frustrating. This stems from the fact that openat(2) is
  possibly the most famous counter-example to the mantra "don't silently
  accept garbage from userspace" -- it doesn't check whether unknown
  flags are present[1].

  This means that (generally) the addition of new flags to openat(2) has
  been fraught with backwards-compatibility issues (O_TMPFILE has to be
  defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old
  kernels gave errors, since it's insecure to silently ignore the
  flag[2]). All new security-related flags therefore have a tough road
  to being added to openat(2).

  Furthermore, the need for some sort of control over VFS's path
  resolution (to avoid malicious paths resulting in inadvertent
  breakouts) has been a very long-standing desire of many userspace
  applications.

  This patchset is a revival of Al Viro's old AT_NO_JUMPS[3] patchset
  (which was a variant of David Drysdale's O_BENEATH patchset[4] which
  was a spin-off of the Capsicum project[5]) with a few additions and
  changes made based on the previous discussion within [6] as well as
  others I felt were useful.

  In line with the conclusions of the original discussion of
  AT_NO_JUMPS, the flag has been split up into separate flags. However,
  instead of being an openat(2) flag it is provided through a new
  syscall openat2(2) which provides several other improvements to the
  openat(2) interface (see the patch description for more details). The
  following new LOOKUP_* flags are added:

  LOOKUP_NO_XDEV:

     Blocks all mountpoint crossings (upwards, downwards, or through
     absolute links). Absolute pathnames alone in openat(2) do not
     trigger this. Magic-link traversal which implies a vfsmount jump is
     also blocked (though magic-link jumps on the same vfsmount are
     permitted).

  LOOKUP_NO_MAGICLINKS:

     Blocks resolution through /proc/$pid/fd-style links. This is done
     by blocking the usage of nd_jump_link() during resolution in a
     filesystem. The term "magic-links" is used to match with the only
     reference to these links in Documentation/, but I'm happy to change
     the name.

     It should be noted that this is different to the scope of
     ~LOOKUP_FOLLOW in that it applies to all path components. However,
     you can do openat2(NO_FOLLOW|NO_MAGICLINKS) on a magic-link and it
     will *not* fail (assuming that no parent component was a
     magic-link), and you will have an fd for the magic-link.

     In order to correctly detect magic-links, the introduction of a new
     LOOKUP_MAGICLINK_JUMPED state flag was required.

  LOOKUP_BENEATH:

     Disallows escapes to outside the starting dirfd's
     tree, using techniques such as ".." or absolute links. Absolute
     paths in openat(2) are also disallowed.

     Conceptually this flag is to ensure you "stay below" a certain
     point in the filesystem tree -- but this requires some additional
     to protect against various races that would allow escape using
     "..".

     Currently LOOKUP_BENEATH implies LOOKUP_NO_MAGICLINKS, because it
     can trivially beam you around the filesystem (breaking the
     protection). In future, there might be similar safety checks done
     as in LOOKUP_IN_ROOT, but that requires more discussion.

  In addition, two new flags are added that expand on the above ideas:

  LOOKUP_NO_SYMLINKS:

     Does what it says on the tin. No symlink resolution is allowed at
     all, including magic-links. Just as with LOOKUP_NO_MAGICLINKS this
     can still be used with NOFOLLOW to open an fd for the symlink as
     long as no parent path had a symlink component.

  LOOKUP_IN_ROOT:

     This is an extension of LOOKUP_BENEATH that, rather than blocking
     attempts to move past the root, forces all such movements to be
     scoped to the starting point. This provides chroot(2)-like
     protection but without the cost of a chroot(2) for each filesystem
     operation, as well as being safe against race attacks that
     chroot(2) is not.

     If a race is detected (as with LOOKUP_BENEATH) then an error is
     generated, and similar to LOOKUP_BENEATH it is not permitted to
     cross magic-links with LOOKUP_IN_ROOT.

     The primary need for this is from container runtimes, which
     currently need to do symlink scoping in userspace[7] when opening
     paths in a potentially malicious container.

     There is a long list of CVEs that could have bene mitigated by
     having RESOLVE_THIS_ROOT (such as CVE-2017-1002101,
     CVE-2017-1002102, CVE-2018-15664, and CVE-2019-5736, just to name a
     few).

  In order to make all of the above more usable, I'm working on
  libpathrs[8] which is a C-friendly library for safe path resolution.
  It features a userspace-emulated backend if the kernel doesn't support
  openat2(2). Hopefully we can get userspace to switch to using it, and
  thus get openat2(2) support for free once it's ready.

  Future work would include implementing things like
  RESOLVE_NO_AUTOMOUNT and possibly a RESOLVE_NO_REMOTE (to allow
  programs to be sure they don't hit DoSes though stale NFS handles)"

* 'work.openat2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  Documentation: path-lookup: include new LOOKUP flags
  selftests: add openat2(2) selftests
  open: introduce openat2(2) syscall
  namei: LOOKUP_{IN_ROOT,BENEATH}: permit limited ".." resolution
  namei: LOOKUP_IN_ROOT: chroot-like scoped resolution
  namei: LOOKUP_BENEATH: O_BENEATH-like scoped resolution
  namei: LOOKUP_NO_XDEV: block mountpoint crossing
  namei: LOOKUP_NO_MAGICLINKS: block magic-link resolution
  namei: LOOKUP_NO_SYMLINKS: block symlink resolution
  namei: allow set_root() to produce errors
  namei: allow nd_jump_link() to produce errors
  nsfs: clean-up ns_get_path() signature to return int
  namei: only return -ECHILD from follow_dotdot_rcu()

1 files changed, 312 insertions, 0 deletions

diff --git a/tools/testing/selftests/openat2/openat2_test.c b/tools/testing/selftests/openat2/openat2_test.c
new file mode 100644
index 000000000000..b386367c606b
--- /dev/null
+++ b/tools/testing/selftests/openat2/openat2_test.c
@@ -0,0 +1,312 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Author: Aleksa Sarai <cyphar@cyphar.com>
+ * Copyright (C) 2018-2019 SUSE LLC.
+ */
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <sched.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/mount.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include "../kselftest.h"
+#include "helpers.h"
+
+/*
+ * O_LARGEFILE is set to 0 by glibc.
+ * XXX: This is wrong on {mips, parisc, powerpc, sparc}.
+ */
+#undef	O_LARGEFILE
+#define	O_LARGEFILE 0x8000
+
+struct open_how_ext {
+	struct open_how inner;
+	uint32_t extra1;
+	char pad1[128];
+	uint32_t extra2;
+	char pad2[128];
+	uint32_t extra3;
+};
+
+struct struct_test {
+	const char *name;
+	struct open_how_ext arg;
+	size_t size;
+	int err;
+};
+
+#define NUM_OPENAT2_STRUCT_TESTS 7
+#define NUM_OPENAT2_STRUCT_VARIATIONS 13
+
+void test_openat2_struct(void)
+{
+	int misalignments[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 17, 87 };
+
+	struct struct_test tests[] = {
+		/* Normal struct. */
+		{ .name = "normal struct",
+		  .arg.inner.flags = O_RDONLY,
+		  .size = sizeof(struct open_how) },
+		/* Bigger struct, with zeroed out end. */
+		{ .name = "bigger struct (zeroed out)",
+		  .arg.inner.flags = O_RDONLY,
+		  .size = sizeof(struct open_how_ext) },
+
+		/* TODO: Once expanded, check zero-padding. */
+
+		/* Smaller than version-0 struct. */
+		{ .name = "zero-sized 'struct'",
+		  .arg.inner.flags = O_RDONLY, .size = 0, .err = -EINVAL },
+		{ .name = "smaller-than-v0 struct",
+		  .arg.inner.flags = O_RDONLY,
+		  .size = OPEN_HOW_SIZE_VER0 - 1, .err = -EINVAL },
+
+		/* Bigger struct, with non-zero trailing bytes. */
+		{ .name = "bigger struct (non-zero data in first 'future field')",
+		  .arg.inner.flags = O_RDONLY, .arg.extra1 = 0xdeadbeef,
+		  .size = sizeof(struct open_how_ext), .err = -E2BIG },
+		{ .name = "bigger struct (non-zero data in middle of 'future fields')",
+		  .arg.inner.flags = O_RDONLY, .arg.extra2 = 0xfeedcafe,
+		  .size = sizeof(struct open_how_ext), .err = -E2BIG },
+		{ .name = "bigger struct (non-zero data at end of 'future fields')",
+		  .arg.inner.flags = O_RDONLY, .arg.extra3 = 0xabad1dea,
+		  .size = sizeof(struct open_how_ext), .err = -E2BIG },
+	};
+
+	BUILD_BUG_ON(ARRAY_LEN(misalignments) != NUM_OPENAT2_STRUCT_VARIATIONS);
+	BUILD_BUG_ON(ARRAY_LEN(tests) != NUM_OPENAT2_STRUCT_TESTS);
+
+	for (int i = 0; i < ARRAY_LEN(tests); i++) {
+		struct struct_test *test = &tests[i];
+		struct open_how_ext how_ext = test->arg;
+
+		for (int j = 0; j < ARRAY_LEN(misalignments); j++) {
+			int fd, misalign = misalignments[j];
+			char *fdpath = NULL;
+			bool failed;
+			void (*resultfn)(const char *msg, ...) = ksft_test_result_pass;
+
+			void *copy = NULL, *how_copy = &how_ext;
+
+			if (!openat2_supported) {
+				ksft_print_msg("openat2(2) unsupported\n");
+				resultfn = ksft_test_result_skip;
+				goto skip;
+			}
+
+			if (misalign) {
+				/*
+				 * Explicitly misalign the structure copying it with the given
+				 * (mis)alignment offset. The other data is set to be non-zero to
+				 * make sure that non-zero bytes outside the struct aren't checked
+				 *
+				 * This is effectively to check that is_zeroed_user() works.
+				 */
+				copy = malloc(misalign + sizeof(how_ext));
+				how_copy = copy + misalign;
+				memset(copy, 0xff, misalign);
+				memcpy(how_copy, &how_ext, sizeof(how_ext));
+			}
+
+			fd = raw_openat2(AT_FDCWD, ".", how_copy, test->size);
+			if (test->err >= 0)
+				failed = (fd < 0);
+			else
+				failed = (fd != test->err);
+			if (fd >= 0) {
+				fdpath = fdreadlink(fd);
+				close(fd);
+			}
+
+			if (failed) {
+				resultfn = ksft_test_result_fail;
+
+				ksft_print_msg("openat2 unexpectedly returned ");
+				if (fdpath)
+					ksft_print_msg("%d['%s']\n", fd, fdpath);
+				else
+					ksft_print_msg("%d (%s)\n", fd, strerror(-fd));
+			}
+
+skip:
+			if (test->err >= 0)
+				resultfn("openat2 with %s argument [misalign=%d] succeeds\n",
+					 test->name, misalign);
+			else
+				resultfn("openat2 with %s argument [misalign=%d] fails with %d (%s)\n",
+					 test->name, misalign, test->err,
+					 strerror(-test->err));
+
+			free(copy);
+			free(fdpath);
+			fflush(stdout);
+		}
+	}
+}
+
+struct flag_test {
+	const char *name;
+	struct open_how how;
+	int err;
+};
+
+#define NUM_OPENAT2_FLAG_TESTS 23
+
+void test_openat2_flags(void)
+{
+	struct flag_test tests[] = {
+		/* O_TMPFILE is incompatible with O_PATH and O_CREAT. */
+		{ .name = "incompatible flags (O_TMPFILE | O_PATH)",
+		  .how.flags = O_TMPFILE | O_PATH | O_RDWR, .err = -EINVAL },
+		{ .name = "incompatible flags (O_TMPFILE | O_CREAT)",
+		  .how.flags = O_TMPFILE | O_CREAT | O_RDWR, .err = -EINVAL },
+
+		/* O_PATH only permits certain other flags to be set ... */
+		{ .name = "compatible flags (O_PATH | O_CLOEXEC)",
+		  .how.flags = O_PATH | O_CLOEXEC },
+		{ .name = "compatible flags (O_PATH | O_DIRECTORY)",
+		  .how.flags = O_PATH | O_DIRECTORY },
+		{ .name = "compatible flags (O_PATH | O_NOFOLLOW)",
+		  .how.flags = O_PATH | O_NOFOLLOW },
+		/* ... and others are absolutely not permitted. */
+		{ .name = "incompatible flags (O_PATH | O_RDWR)",
+		  .how.flags = O_PATH | O_RDWR, .err = -EINVAL },
+		{ .name = "incompatible flags (O_PATH | O_CREAT)",
+		  .how.flags = O_PATH | O_CREAT, .err = -EINVAL },
+		{ .name = "incompatible flags (O_PATH | O_EXCL)",
+		  .how.flags = O_PATH | O_EXCL, .err = -EINVAL },
+		{ .name = "incompatible flags (O_PATH | O_NOCTTY)",
+		  .how.flags = O_PATH | O_NOCTTY, .err = -EINVAL },
+		{ .name = "incompatible flags (O_PATH | O_DIRECT)",
+		  .how.flags = O_PATH | O_DIRECT, .err = -EINVAL },
+		{ .name = "incompatible flags (O_PATH | O_LARGEFILE)",
+		  .how.flags = O_PATH | O_LARGEFILE, .err = -EINVAL },
+
+		/* ->mode must only be set with O_{CREAT,TMPFILE}. */
+		{ .name = "non-zero how.mode and O_RDONLY",
+		  .how.flags = O_RDONLY, .how.mode = 0600, .err = -EINVAL },
+		{ .name = "non-zero how.mode and O_PATH",
+		  .how.flags = O_PATH,   .how.mode = 0600, .err = -EINVAL },
+		{ .name = "valid how.mode and O_CREAT",
+		  .how.flags = O_CREAT,  .how.mode = 0600 },
+		{ .name = "valid how.mode and O_TMPFILE",
+		  .how.flags = O_TMPFILE | O_RDWR, .how.mode = 0600 },
+		/* ->mode must only contain 0777 bits. */
+		{ .name = "invalid how.mode and O_CREAT",
+		  .how.flags = O_CREAT,
+		  .how.mode = 0xFFFF, .err = -EINVAL },
+		{ .name = "invalid (very large) how.mode and O_CREAT",
+		  .how.flags = O_CREAT,
+		  .how.mode = 0xC000000000000000ULL, .err = -EINVAL },
+		{ .name = "invalid how.mode and O_TMPFILE",
+		  .how.flags = O_TMPFILE | O_RDWR,
+		  .how.mode = 0x1337, .err = -EINVAL },
+		{ .name = "invalid (very large) how.mode and O_TMPFILE",
+		  .how.flags = O_TMPFILE | O_RDWR,
+		  .how.mode = 0x0000A00000000000ULL, .err = -EINVAL },
+
+		/* ->resolve must only contain RESOLVE_* flags. */
+		{ .name = "invalid how.resolve and O_RDONLY",
+		  .how.flags = O_RDONLY,
+		  .how.resolve = 0x1337, .err = -EINVAL },
+		{ .name = "invalid how.resolve and O_CREAT",
+		  .how.flags = O_CREAT,
+		  .how.resolve = 0x1337, .err = -EINVAL },
+		{ .name = "invalid how.resolve and O_TMPFILE",
+		  .how.flags = O_TMPFILE | O_RDWR,
+		  .how.resolve = 0x1337, .err = -EINVAL },
+		{ .name = "invalid how.resolve and O_PATH",
+		  .how.flags = O_PATH,
+		  .how.resolve = 0x1337, .err = -EINVAL },
+	};
+
+	BUILD_BUG_ON(ARRAY_LEN(tests) != NUM_OPENAT2_FLAG_TESTS);
+
+	for (int i = 0; i < ARRAY_LEN(tests); i++) {
+		int fd, fdflags = -1;
+		char *path, *fdpath = NULL;
+		bool failed = false;
+		struct flag_test *test = &tests[i];
+		void (*resultfn)(const char *msg, ...) = ksft_test_result_pass;
+
+		if (!openat2_supported) {
+			ksft_print_msg("openat2(2) unsupported\n");
+			resultfn = ksft_test_result_skip;
+			goto skip;
+		}
+
+		path = (test->how.flags & O_CREAT) ? "/tmp/ksft.openat2_tmpfile" : ".";
+		unlink(path);
+
+		fd = sys_openat2(AT_FDCWD, path, &test->how);
+		if (test->err >= 0)
+			failed = (fd < 0);
+		else
+			failed = (fd != test->err);
+		if (fd >= 0) {
+			int otherflags;
+
+			fdpath = fdreadlink(fd);
+			fdflags = fcntl(fd, F_GETFL);
+			otherflags = fcntl(fd, F_GETFD);
+			close(fd);
+
+			E_assert(fdflags >= 0, "fcntl F_GETFL of new fd");
+			E_assert(otherflags >= 0, "fcntl F_GETFD of new fd");
+
+			/* O_CLOEXEC isn't shown in F_GETFL. */
+			if (otherflags & FD_CLOEXEC)
+				fdflags |= O_CLOEXEC;
+			/* O_CREAT is hidden from F_GETFL. */
+			if (test->how.flags & O_CREAT)
+				fdflags |= O_CREAT;
+			if (!(test->how.flags & O_LARGEFILE))
+				fdflags &= ~O_LARGEFILE;
+			failed |= (fdflags != test->how.flags);
+		}
+
+		if (failed) {
+			resultfn = ksft_test_result_fail;
+
+			ksft_print_msg("openat2 unexpectedly returned ");
+			if (fdpath)
+				ksft_print_msg("%d['%s'] with %X (!= %X)\n",
+					       fd, fdpath, fdflags,
+					       test->how.flags);
+			else
+				ksft_print_msg("%d (%s)\n", fd, strerror(-fd));
+		}
+
+skip:
+		if (test->err >= 0)
+			resultfn("openat2 with %s succeeds\n", test->name);
+		else
+			resultfn("openat2 with %s fails with %d (%s)\n",
+				 test->name, test->err, strerror(-test->err));
+
+		free(fdpath);
+		fflush(stdout);
+	}
+}
+
+#define NUM_TESTS (NUM_OPENAT2_STRUCT_VARIATIONS * NUM_OPENAT2_STRUCT_TESTS + \
+		   NUM_OPENAT2_FLAG_TESTS)
+
+int main(int argc, char **argv)
+{
+	ksft_print_header();
+	ksft_set_plan(NUM_TESTS);
+
+	test_openat2_struct();
+	test_openat2_flags();
+
+	if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0)
+		ksft_exit_fail();
+	else
+		ksft_exit_pass();
+}