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diff --git a/etc/mtree/BSD.tests.dist b/etc/mtree/BSD.tests.dist
--- a/etc/mtree/BSD.tests.dist
+++ b/etc/mtree/BSD.tests.dist
@@ -828,6 +828,8 @@
file
..
fs
+ fdescfs
+ ..
fusefs
..
pjdfstest
diff --git a/share/man/man4/fdescfs.4 b/share/man/man4/fdescfs.4
--- a/share/man/man4/fdescfs.4
+++ b/share/man/man4/fdescfs.4
@@ -38,7 +38,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
-.Dd Jul 11, 2023
+.Dd September 6, 2026
.Dt FDESCFS 4
.Os
.Sh NAME
@@ -85,6 +85,11 @@
.Fx
traditional
.Dv VCHR .
+Path components following a directory descriptor entry are resolved relative
+to the referenced directory.
+A trailing slash also resolves to the referenced directory.
+Opening an entry as the last path component, without a trailing slash,
+retains the behavior described below.
For
.Xr linux 4
ABI compatibility mount
diff --git a/sys/fs/fdescfs/fdesc_vnops.c b/sys/fs/fdescfs/fdesc_vnops.c
--- a/sys/fs/fdescfs/fdesc_vnops.c
+++ b/sys/fs/fdescfs/fdesc_vnops.c
@@ -248,6 +248,7 @@
struct file *fp;
struct thread *td;
bool fdropped;
+ bool traverse;
};
static int
@@ -261,7 +262,8 @@
a = arg;
fdm = VFSTOFDESC(mp);
- if ((fdm->flags & FMNT_NODUP) != 0 && a->fp->f_type == DTYPE_VNODE) {
+ if ((a->traverse || (fdm->flags & FMNT_NODUP) != 0) &&
+ a->fp->f_type == DTYPE_VNODE) {
vp = a->fp->f_vnode;
vget(vp, lkflags | LK_RETRY);
*rvp = vp;
@@ -292,6 +294,7 @@
u_int fd, fd1;
int error;
struct vnode *fvp;
+ bool traverse;
if ((cnp->cn_flags & ISLASTCN) &&
(cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
@@ -335,6 +338,16 @@
if ((error = fget(td, fd, &cap_no_rights, &fp)) != 0)
goto bad;
+ /* A component below /dev/fd/N resolves in the directory N names. */
+ traverse = ((cnp->cn_flags & ISLASTCN) == 0 ||
+ (cnp->cn_flags & TRAILINGSLASH) != 0) &&
+ (VFSTOFDESC(dvp->v_mount)->flags & FMNT_LINRDLNKF) != 0;
+ if (traverse && fp->f_type != DTYPE_VNODE) {
+ fdrop(fp, td);
+ error = ENOTDIR;
+ goto bad;
+ }
+
/*
* Make sure we do not deadlock looking up the dvp itself.
*
@@ -350,6 +363,7 @@
arg.fp = fp;
arg.td = td;
arg.fdropped = false;
+ arg.traverse = traverse;
error = vn_vget_ino_gen(dvp, fdesc_get_ino_alloc, &arg,
LK_EXCLUSIVE, &fvp);
diff --git a/tests/sys/fs/Makefile b/tests/sys/fs/Makefile
--- a/tests/sys/fs/Makefile
+++ b/tests/sys/fs/Makefile
@@ -7,6 +7,7 @@
TESTSRC= ${SRCTOP}/contrib/netbsd-tests/fs
+TESTS_SUBDIRS+= fdescfs
TESTS_SUBDIRS+= nullfs
# fusefs tests cannot be compiled/used without the googletest infrastructure.
.if ${COMPILER_FEATURES:Mc++14} && ${MK_GOOGLETEST} != "no"
diff --git a/tests/sys/fs/fdescfs/Makefile b/tests/sys/fs/fdescfs/Makefile
new file mode 100644
--- /dev/null
+++ b/tests/sys/fs/fdescfs/Makefile
@@ -0,0 +1,9 @@
+PACKAGE= tests
+
+TESTSDIR= ${TESTSBASE}/sys/fs/fdescfs
+
+ATF_TESTS_C+= fdescfs_test
+
+LIBADD+= util
+
+.include <bsd.test.mk>
diff --git a/tests/sys/fs/fdescfs/fdescfs_test.c b/tests/sys/fs/fdescfs/fdescfs_test.c
new file mode 100644
--- /dev/null
+++ b/tests/sys/fs/fdescfs/fdescfs_test.c
@@ -0,0 +1,373 @@
+#include <sys/param.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+
+#include <atf-c.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <mntopts.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static const char *const linrdlnk[] = { "linrdlnk", NULL };
+static const char *const nodup_linrdlnk[] = { "nodup", "linrdlnk", NULL };
+
+static void
+mount_fdescfs(const char *const *opts)
+{
+ struct iovec *iov;
+ char errmsg[256];
+ int error, iovlen;
+
+ ATF_REQUIRE_EQ(0, mkdir("mnt", 0755));
+ iov = NULL;
+ iovlen = 0;
+ build_iovec(&iov, &iovlen, __DECONST(char *, "fstype"),
+ __DECONST(char *, "fdescfs"), (size_t)-1);
+ build_iovec(&iov, &iovlen, __DECONST(char *, "fspath"),
+ __DECONST(char *, "mnt"), (size_t)-1);
+ for (; opts != NULL && *opts != NULL; opts++)
+ build_iovec(&iov, &iovlen, __DECONST(char *, *opts), NULL,
+ (size_t)-1);
+ build_iovec(&iov, &iovlen, __DECONST(char *, "errmsg"), errmsg,
+ sizeof(errmsg));
+ errmsg[0] = '\0';
+ error = nmount(iov, iovlen, 0);
+ if (error != 0 && errno == ENODEV)
+ atf_tc_skip("fdescfs is not available");
+ ATF_REQUIRE_MSG(error == 0, "nmount: %s",
+ errmsg[0] != '\0' ? errmsg : strerror(errno));
+ free_iovec(&iov, &iovlen);
+}
+
+static void
+fdpath(char *path, size_t size, int fd, const char *suffix)
+{
+ int len;
+
+ len = snprintf(path, size, "mnt/%d%s", fd, suffix);
+ ATF_REQUIRE(len > 0 && (size_t)len < size);
+}
+
+static void
+create_directory(const char *path, char marker)
+{
+ int dirfd, fd;
+
+ ATF_REQUIRE_EQ(0, mkdir(path, 0755));
+ ATF_REQUIRE((dirfd = open(path, O_RDONLY | O_DIRECTORY)) >= 0);
+ ATF_REQUIRE(
+ (fd = openat(dirfd, "marker", O_WRONLY | O_CREAT, 0644)) >= 0);
+ ATF_REQUIRE_EQ(1, write(fd, &marker, 1));
+ ATF_REQUIRE_EQ(0, close(fd));
+ ATF_REQUIRE_EQ(0, close(dirfd));
+}
+
+static void
+check_identity(const struct stat *expected, const struct stat *actual)
+{
+ ATF_CHECK_EQ(expected->st_dev, actual->st_dev);
+ ATF_CHECK_EQ(expected->st_ino, actual->st_ino);
+ ATF_CHECK_EQ(expected->st_mode & S_IFMT, actual->st_mode & S_IFMT);
+}
+
+static void
+check_directory(int dirfd, const char *suffix)
+{
+ struct stat expected, actual;
+ char path[64];
+ int fd;
+
+ fdpath(path, sizeof(path), dirfd, suffix);
+ ATF_REQUIRE_EQ(0, fstat(dirfd, &expected));
+ ATF_REQUIRE_MSG(stat(path, &actual) == 0, "stat(%s): %s", path,
+ strerror(errno));
+ check_identity(&expected, &actual);
+ ATF_REQUIRE_MSG((fd = open(path, O_RDONLY | O_DIRECTORY)) >= 0,
+ "open(%s): %s", path, strerror(errno));
+ ATF_REQUIRE_EQ(0, fstat(fd, &actual));
+ check_identity(&expected, &actual);
+ ATF_REQUIRE_EQ(0, close(fd));
+}
+
+static void
+check_marker(int dirfd, char expected)
+{
+ char path[64], actual;
+ int fd;
+
+ fdpath(path, sizeof(path), dirfd, "/marker");
+ ATF_REQUIRE_MSG((fd = open(path, O_RDONLY)) >= 0, "open(%s): %s", path,
+ strerror(errno));
+ ATF_REQUIRE_EQ(1, read(fd, &actual, 1));
+ ATF_CHECK_EQ(expected, actual);
+ ATF_REQUIRE_EQ(0, close(fd));
+}
+
+static void
+check_bare(int fd, const char *target)
+{
+ struct stat sb;
+ char path[64], expected[PATH_MAX], actual[PATH_MAX];
+ ssize_t len;
+ int copy, flags, actual_flags;
+
+ fdpath(path, sizeof(path), fd, "");
+ ATF_REQUIRE_EQ(0, lstat(path, &sb));
+ ATF_CHECK(S_ISLNK(sb.st_mode));
+ ATF_REQUIRE(realpath(target, expected) != NULL);
+ ATF_REQUIRE((len = readlink(path, actual, sizeof(actual))) >= 0);
+ ATF_REQUIRE_EQ(strlen(expected), (size_t)len);
+ ATF_CHECK_EQ(0, memcmp(expected, actual, len));
+ ATF_REQUIRE((copy = open(path, O_RDONLY)) >= 0);
+ ATF_REQUIRE((flags = fcntl(fd, F_GETFL)) >= 0);
+ ATF_REQUIRE_EQ(0, fcntl(copy, F_SETFL, flags ^ O_NONBLOCK));
+ ATF_REQUIRE((actual_flags = fcntl(fd, F_GETFL)) >= 0);
+ ATF_CHECK_EQ((flags ^ O_NONBLOCK) & O_NONBLOCK,
+ actual_flags & O_NONBLOCK);
+ ATF_REQUIRE_EQ(0, fcntl(fd, F_SETFL, flags));
+ ATF_REQUIRE_EQ(0, close(copy));
+}
+
+static void
+check_open_offset(bool duplicate)
+{
+ char path[64], buf[2], byte;
+ int fd, copy;
+
+ ATF_REQUIRE((fd = open("file", O_RDWR | O_CREAT, 0644)) >= 0);
+ ATF_REQUIRE_EQ(6, write(fd, "abcdef", 6));
+ ATF_REQUIRE_EQ(0, lseek(fd, 0, SEEK_SET));
+ ATF_REQUIRE_EQ(2, read(fd, buf, sizeof(buf)));
+ ATF_REQUIRE_EQ(0, memcmp(buf, "ab", sizeof(buf)));
+ fdpath(path, sizeof(path), fd, "");
+ ATF_REQUIRE((copy = open(path, O_RDONLY)) >= 0);
+ ATF_CHECK_EQ(duplicate ? 2 : 0, lseek(copy, 0, SEEK_CUR));
+ ATF_REQUIRE_EQ(1, read(copy, &byte, 1));
+ ATF_CHECK_EQ(duplicate ? 'c' : 'a', byte);
+ ATF_CHECK_EQ(duplicate ? 3 : 2, lseek(fd, 0, SEEK_CUR));
+ ATF_REQUIRE_EQ(0, close(copy));
+ ATF_REQUIRE_EQ(0, close(fd));
+}
+
+static void
+check_notdir(int fd)
+{
+ const char *suffixes[] = { "/child", "/" };
+ char path[64];
+ size_t i;
+
+ for (i = 0; i < nitems(suffixes); i++) {
+ fdpath(path, sizeof(path), fd, suffixes[i]);
+ ATF_REQUIRE_ERRNO(ENOTDIR, open(path, O_RDONLY) == -1);
+ }
+}
+
+static void
+check_traverse(int flags)
+{
+ struct stat expected, actual;
+ char path[64];
+ int fd;
+
+ mount_fdescfs(linrdlnk);
+ ATF_REQUIRE_EQ(0, mkdir("parent", 0755));
+ create_directory("parent/target", 'a');
+ ATF_REQUIRE((fd = open("parent/target", flags | O_DIRECTORY)) >= 0);
+ fdpath(path, sizeof(path), fd, "/..");
+ ATF_REQUIRE_EQ(0, stat("parent", &expected));
+ ATF_REQUIRE_MSG(stat(path, &actual) == 0, "stat(%s): %s", path,
+ strerror(errno));
+ check_identity(&expected, &actual);
+ check_marker(fd, 'a');
+ fdpath(path, sizeof(path), fd, "/child");
+ ATF_REQUIRE_MSG(mkdir(path, 0755) == 0, "mkdir(%s): %s", path,
+ strerror(errno));
+ ATF_REQUIRE_EQ(0, stat("parent/target/child", &expected));
+ ATF_REQUIRE_EQ(0, stat(path, &actual));
+ ATF_CHECK(S_ISDIR(actual.st_mode));
+ check_identity(&expected, &actual);
+ ATF_REQUIRE_EQ(0, close(fd));
+ ATF_REQUIRE_EQ(0, unmount("mnt", 0));
+}
+
+#define FDESCFS_TC(name, description) \
+ ATF_TC_WITH_CLEANUP(name); \
+ ATF_TC_HEAD(name, tc) \
+ { \
+ atf_tc_set_md_var(tc, "descr", description); \
+ atf_tc_set_md_var(tc, "require.user", "root"); \
+ atf_tc_set_md_var(tc, "timeout", "30"); \
+ } \
+ ATF_TC_CLEANUP(name, tc) \
+ { \
+ (void)unmount("mnt", 0); \
+ }
+
+FDESCFS_TC(traverse_dir, "Traverse a directory descriptor under linrdlnk");
+ATF_TC_BODY(traverse_dir, tc)
+{
+ check_traverse(O_RDONLY);
+}
+
+FDESCFS_TC(traverse_path, "Traverse an O_PATH descriptor under linrdlnk");
+ATF_TC_BODY(traverse_path, tc)
+{
+ check_traverse(O_PATH);
+}
+
+FDESCFS_TC(trailing_slash,
+ "Trailing slashes resolve to the referenced directory");
+ATF_TC_BODY(trailing_slash, tc)
+{
+ const int flags[] = { O_RDONLY, O_PATH };
+ size_t i;
+ int fd;
+
+ mount_fdescfs(linrdlnk);
+ create_directory("target", 'a');
+ for (i = 0; i < nitems(flags); i++) {
+ ATF_REQUIRE((fd = open("target", flags[i] | O_DIRECTORY)) >= 0);
+ check_directory(fd, "/");
+ ATF_REQUIRE_EQ(0, close(fd));
+ }
+ ATF_REQUIRE_EQ(0, unmount("mnt", 0));
+}
+
+FDESCFS_TC(last_component_dups,
+ "Bare linrdlnk opens share the original offset");
+ATF_TC_BODY(last_component_dups, tc)
+{
+ mount_fdescfs(linrdlnk);
+ check_open_offset(true);
+ ATF_REQUIRE_EQ(0, unmount("mnt", 0));
+}
+
+FDESCFS_TC(lookup_order,
+ "Bare and traversing lookups do not affect each other");
+ATF_TC_BODY(lookup_order, tc)
+{
+ int first, second;
+
+ mount_fdescfs(linrdlnk);
+ create_directory("target", 'a');
+ ATF_REQUIRE((first = open("target", O_RDONLY | O_DIRECTORY)) >= 0);
+ ATF_REQUIRE((second = open("target", O_RDONLY | O_DIRECTORY)) >= 0);
+ check_bare(first, "target");
+ check_marker(first, 'a');
+ check_directory(first, "/");
+ check_bare(first, "target");
+ check_marker(second, 'a');
+ check_directory(second, "/");
+ check_bare(second, "target");
+ check_marker(second, 'a');
+ ATF_REQUIRE_EQ(0, close(second));
+ ATF_REQUIRE_EQ(0, close(first));
+ ATF_REQUIRE_EQ(0, unmount("mnt", 0));
+}
+
+FDESCFS_TC(descriptor_reuse, "Reusing a descriptor selects its current target");
+ATF_TC_BODY(descriptor_reuse, tc)
+{
+ int fd, replacement;
+
+ mount_fdescfs(linrdlnk);
+ create_directory("first", 'a');
+ create_directory("second", 'b');
+ ATF_REQUIRE((fd = open("first", O_RDONLY | O_DIRECTORY)) >= 0);
+ check_bare(fd, "first");
+ check_marker(fd, 'a');
+ ATF_REQUIRE(
+ (replacement = open("second", O_RDONLY | O_DIRECTORY)) >= 0);
+ ATF_REQUIRE_EQ(fd, dup2(replacement, fd));
+ ATF_REQUIRE_EQ(0, close(replacement));
+ check_marker(fd, 'b');
+ check_directory(fd, "/");
+ check_bare(fd, "second");
+ ATF_REQUIRE((replacement = open("second/marker", O_RDONLY)) >= 0);
+ ATF_REQUIRE_EQ(fd, dup2(replacement, fd));
+ ATF_REQUIRE_EQ(0, close(replacement));
+ check_notdir(fd);
+ check_bare(fd, "second/marker");
+ ATF_REQUIRE_EQ(0, close(fd));
+ ATF_REQUIRE_EQ(0, unmount("mnt", 0));
+}
+
+FDESCFS_TC(traverse_nondir, "Files and pipes reject traversal");
+ATF_TC_BODY(traverse_nondir, tc)
+{
+ int fd, pipes[2];
+
+ mount_fdescfs(linrdlnk);
+ ATF_REQUIRE((fd = open("file", O_RDONLY | O_CREAT, 0644)) >= 0);
+ check_notdir(fd);
+ ATF_REQUIRE_EQ(0, close(fd));
+ ATF_REQUIRE_EQ(0, pipe(pipes));
+ check_notdir(pipes[0]);
+ ATF_REQUIRE_EQ(0, close(pipes[0]));
+ ATF_REQUIRE_EQ(0, close(pipes[1]));
+ ATF_REQUIRE_EQ(0, unmount("mnt", 0));
+}
+
+FDESCFS_TC(plain_mount, "Plain mounts reject traversal");
+ATF_TC_BODY(plain_mount, tc)
+{
+ int fd;
+
+ mount_fdescfs(NULL);
+ create_directory("target", 'a');
+ ATF_REQUIRE((fd = open("target", O_RDONLY | O_DIRECTORY)) >= 0);
+ check_notdir(fd);
+ ATF_REQUIRE_EQ(0, close(fd));
+ ATF_REQUIRE_EQ(0, unmount("mnt", 0));
+}
+
+FDESCFS_TC(nodup_linrdlnk_mount, "Linrdlnk preserves nodup behavior");
+ATF_TC_BODY(nodup_linrdlnk_mount, tc)
+{
+ int fd;
+
+ mount_fdescfs(nodup_linrdlnk);
+ create_directory("target", 'a');
+ ATF_REQUIRE((fd = open("target", O_RDONLY | O_DIRECTORY)) >= 0);
+ check_marker(fd, 'a');
+ check_directory(fd, "/");
+ ATF_REQUIRE_EQ(0, close(fd));
+ check_open_offset(false);
+ ATF_REQUIRE_EQ(0, unmount("mnt", 0));
+}
+
+FDESCFS_TC(root_reference,
+ "Traverse a descriptor referencing the fdescfs root");
+ATF_TC_BODY(root_reference, tc)
+{
+ char suffix[32];
+ int fd, len;
+
+ mount_fdescfs(linrdlnk);
+ ATF_REQUIRE((fd = open("mnt", O_RDONLY | O_DIRECTORY)) >= 0);
+ check_directory(fd, "/");
+ len = snprintf(suffix, sizeof(suffix), "/%d/", fd);
+ ATF_REQUIRE(len > 0 && (size_t)len < sizeof(suffix));
+ check_directory(fd, suffix);
+ ATF_REQUIRE_EQ(0, close(fd));
+ ATF_REQUIRE_EQ(0, unmount("mnt", 0));
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+ ATF_TP_ADD_TC(tp, traverse_dir);
+ ATF_TP_ADD_TC(tp, traverse_path);
+ ATF_TP_ADD_TC(tp, trailing_slash);
+ ATF_TP_ADD_TC(tp, last_component_dups);
+ ATF_TP_ADD_TC(tp, lookup_order);
+ ATF_TP_ADD_TC(tp, descriptor_reuse);
+ ATF_TP_ADD_TC(tp, traverse_nondir);
+ ATF_TP_ADD_TC(tp, plain_mount);
+ ATF_TP_ADD_TC(tp, nodup_linrdlnk_mount);
+ ATF_TP_ADD_TC(tp, root_reference);
+ return (atf_no_error());
+}

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